IDR WorkGroup
Internet Engineering Task Force (IETF) D. Rao, Ed.
Internet-Draft
Request for Comments: 9871 S. Agrawal, Ed.
Intended status:
Category: Experimental Cisco Systems
Expires: 24 August 2025 20 February
ISSN: 2070-1721 September 2025
BGP Color-Aware Routing (CAR)
draft-ietf-idr-bgp-car-16
Abstract
This document describes a BGP based BGP-based routing solution to establish
end-to-end intent-aware paths across a multi-domain transport
network. The transport network can span multiple service provider
and customer network domains. The BGP intent-aware paths can be used
to steer traffic flows for service routes that need a specific
intent. This solution is called BGP Color-Aware Routing (BGP CAR).
This document describes the routing framework and BGP extensions to
enable intent-aware routing using the BGP CAR solution. The solution
defines two new BGP SAFIs (BGP CAR SAFI and BGP VPN CAR SAFI) for
IPv4 and IPv6. It also defines an extensible NLRI Network Layer
Reachability Information (NLRI) model for both SAFIs that allow allows
multiple NLRI types to be defined for different use cases. Each type
of NLRI contains key and TLV based TLV-based non-key fields for efficient
encoding of different per-prefix information. This specification
defines two NLRI types, types: Color-Aware Route NLRI and IP Prefix NLRI.
It defines non-key TLV types for the MPLS label stack, stack -- Label Index
and SRv6 SIDs. and Segment Routing over IPv6 (SRv6) Segment Identifiers (SIDs).
This solution also defines a new Local Color Mapping (LCM) Extended
Community.
Status of This Memo
This Internet-Draft document is submitted in full conformance with the
provisions of BCP 78 not an Internet Standards Track specification; it is
published for examination, experimental implementation, and BCP 79.
Internet-Drafts are working documents
evaluation.
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This Internet-Draft will expire on 24 August 2025.
https://www.rfc-editor.org/info/rfc9871.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Illustration . . . . . . . . . . . . . . . . . . . . . . 9
1.3. Requirements Language . . . . . . . . . . . . . . . . . . 11
2. BGP CAR SAFI . . . . . . . . . . . . . . . . . . . . . . . . 11
2.1. Data Model . . . . . . . . . . . . . . . . . . . . . . . 11
2.2. Extensible Encoding . . . . . . . . . . . . . . . . . . . 12
2.3. BGP CAR Route Origination . . . . . . . . . . . . . . . . 13
2.4. BGP CAR Route Validation . . . . . . . . . . . . . . . . 13
2.5. BGP CAR Route Resolution . . . . . . . . . . . . . . . . 13
2.6. AIGP Metric Computation . . . . . . . . . . . . . . . . . 15
2.7. Native MultiPath Multipath Capability . . . . . . . . . . . . . . . 15
2.8. BGP CAR Signaling through different Through Different Color Domains . . . . 16
2.9. Format and Encoding . . . . . . . . . . . . . . . . . . . 17
2.9.1. BGP CAR SAFI NLRI Format . . . . . . . . . . . . . . 18
2.9.2. Type-Specific Non-Key TLV Format . . . . . . . . . . 19
2.9.3. Color-Aware Route (E, C) NLRI Type . . . . . . . . . 23
2.9.4. IP Prefix (E) NLRI Type . . . . . . . . . . . . . . . 25
2.9.5. Local-Color-Mapping (LCM) Extended-Community . . . . 26
2.10. LCM-EC and BGP Color-EC usage . . . . . . . . . . . . . . 27 Usage
2.11. Error Handling . . . . . . . . . . . . . . . . . . . . . 28
3. Service Route Automated Steering on Color-Aware Path . . . . 30 Paths
4. Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . 30
5. Scaling . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.1. Ultra-Scale Reference Topology . . . . . . . . . . . . . 32
5.2. Deployment Model . . . . . . . . . . . . . . . . . . . . 33
5.2.1. Flat . . . . . . . . . . . . . . . . . . . . . . . . 33
5.2.2. Hierarchical Design with Next-Hop-Self at Ingress
Domain BR . . . . . . . . . . . . . . . . . . . . . . 34
5.2.3. Hierarchical Design with Next-Hop-Unchanged at Ingress
Domain BR . . . . . . . . . . . . . . . . . . . . . . 36
5.3. Scale Analysis . . . . . . . . . . . . . . . . . . . . . 37
5.4. Anycast SID . . . . . . . . . . . . . . . . . . . . . . . 39
5.4.1. Anycast SID for Transit Inter-domain Inter-Domain Nodes . . . . . 39
5.4.2. Anycast SID for Transport Color Endpoints (e.g.,
PEs) . . . . . . . . . . . . . . . . . . . . . . . . 39
6. Routing Convergence . . . . . . . . . . . . . . . . . . . . . 40
7. CAR SRv6 . . . . . . . . . . . . . . . . . . . . . . . . . . 40
7.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 40
7.1.1. Routed Service SID . . . . . . . . . . . . . . . . . 40
7.1.2. Non-routed Non-Routed Service SID . . . . . . . . . . . . . . . 41
7.2. Deployment Options For for CAR SRv6 Locator Reachability
Distribution and Forwarding . . . . . . . . . . . . . . . 43
7.2.1. Hop by Hop Hop-by-Hop IPv6 Forwarding for BGP SRv6 Prefixes . . 43
7.2.2. Encapsulation between Between BRs for BGP SRv6 Prefixes . . . 44
7.3. Operational Benefits of using Using CAR SAFI for SRv6 Locator
Prefix Distribution . . . . . . . . . . . . . . . . . . . 45
8. CAR IP Prefix Route . . . . . . . . . . . . . . . . . . . . . 45
9. VPN CAR . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
9.1. Format and Encoding . . . . . . . . . . . . . . . . . . . 48
9.1.1. VPN CAR (E, C) NLRI Type . . . . . . . . . . . . . . 49
9.1.2. VPN CAR IP Prefix NLRI Type . . . . . . . . . . . . . 50
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 50
10.1. BGP CAR SAFIs . . . . . . . . . . . . . . . . . . . . . 50
10.2. BGP "BGP CAR NLRI Types Types" Registry . . . . . . . . . . . . . . 51
10.3. BGP "BGP CAR NLRI TLV TLV" Registry . . . . . . . . . . . . . . . 51
10.4. Guidance for Designated Experts . . . . . . . . . . . . 51
10.4.1. Additional evaluation criteria Evaluation Criteria for the BGP "BGP CAR NLRI
Types
Types" Registry . . . . . . . . . . . . . . . . . . . 52
10.4.2. Additional evaluation criteria Evaluation Criteria for the BGP "BGP CAR NLRI
TLV
TLV" Registry . . . . . . . . . . . . . . . . . . . . 52
10.5. BGP Extended-Community "Border Gateway Protocol (BGP) Extended Communities"
Registry . . . . . . . . . . . . 52
11. Manageability and Operational Considerations . . . . . . . . 53
12. Security Considerations . . . . . . . . . . . . . . . . . . . 53
13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 54
13.1. Co-authors . . . . . . . . . . . . . . . . . . . . . . . 55
13.2. Additional Contributors . . . . . . . . . . . . . . . . 56
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 56
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 56
15.1.
13.1. Normative References . . . . . . . . . . . . . . . . . . 56
15.2.
13.2. Informative References . . . . . . . . . . . . . . . . . 58
Appendix A. Illustrations of Service Steering . . . . . . . . . 60
A.1. E2E BGP transport Transport CAR intent realized using Intent Realized Using IGP Flex-Algo . . . . . . . . . . . . . . . . . . . . . . . . 60
A.2. E2E BGP transport Transport CAR intent realized using Intent Realized Using SR Policy . . 62
A.3. BGP transport Transport CAR intent realized Intent Realized in a section Section of the
network . . . . . . . . . . . . . . . . . . . . . . . . . 64
Network
A.3.1. Provide intent Intent for service flows only Service Flows Only in core domain
running Core Domain
Running IS-IS Flex-Algo . . . . . . . . . . . . . . . 64
A.3.2. Provide intent Intent for service flows only Service Flows Only in core domain Core Domain
over TE tunnel mesh . . . . . . . . . . . . . . . . . 66 Tunnel Mesh
A.4. Transit network domains that do not support Network Domains That Do Not Support CAR . . . . . 68
A.5. Resource Avoidance using Using BGP CAR and IGP Flex-Algo . . . 69
A.6. Per-Flow Steering over CAR routes . . . . . . . . . . . . 71 Routes
A.7. Advertising BGP CAR routes Routes for shared Shared IP addresses . . . 72 Addresses
Appendix B. Color Mapping Illustrations . . . . . . . . . . . . 74
B.1. Single color domain containing network domains Color Domain Containing Network Domains with N:N
color distribution . . . . . . . . . . . . . . . . . . . 74
Color Distribution
B.2. Single color domain containing network domains Color Domain Containing Network Domains with N:M
color distribution . . . . . . . . . . . . . . . . . . . 74
Color Distribution
B.3. Multiple color domains . . . . . . . . . . . . . . . . . 78 Color Domains
Appendix C. CAR SRv6 Illustrations . . . . . . . . . . . . . . . 79
C.1. BGP CAR SRv6 locator reachability hop by hop
distribution . . . . . . . . . . . . . . . . . . . . . . 79 Locator Reachability Hop-by-Hop Distribution
C.2. BGP CAR SRv6 locator reachability distribution Locator Reachability Distribution with
encapsulation . . . . . . . . . . . . . . . . . . . . . . 82
Encapsulation
C.3. BGP CAR (E, C) route distribution Route Distribution for steering non-routed
service Steering Non-Routed
Service SID . . . . . . . . . . . . . . . . . . . . . . . 84
Appendix D. CAR SAFI NLRI update packing efficiency
calculation . . . . . . . . . . . . . . . . . . . . . . . 87 Update Packing Efficiency Calculation
Acknowledgements
Contributors
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 91
1. Introduction
BGP Color-Aware Routing (CAR) is a BGP based BGP-based routing solution to
establish end-to-end intent-aware paths across a multi-domain service
provider transport network. BGP CAR distributes distinct routes to a
destination network endpoint, such as a PE Provider Edge (PE) router,
for different intents or colors. Color is a non-zero 32-bit integer
value associated with a network intent (low-cost, low-delay, (such as low cost, low delay,
avoid some resources, 5G network slice, etc.) as defined in
Section 2.1 of [RFC9256].
BGP CAR fulfills the transport and VPN problem statement and the
requirements described in
[I-D.hr-spring-intentaware-routing-using-color]. [INTENT-AWARE].
For this purpose, this document specifies two new BGP SAFIs, called
BGP CAR SAFI (83) and VPN CAR SAFI (84) (84), that carry infrastructure
routes to set up the transport paths. Both CAR SAFI and VPN CAR SAFI
apply to IPv4 Unicast and IPv6 Unicast AFIs (AFI 1 and AFI 2). The
use of these SAFIs with other AFIs are outside the scope of this
document.
BGP CAR SAFI can be enabled on transport devices in a provider
network (underlay) to set up color-aware transport/infrastructure
paths across provider networks. The multi-domain transport network
may comprise of multiple BGP ASes Autonomous Systems (ASes) as well as
multiple IGP domains within a single BGP AS. BGP CAR SAFI can also
be enabled within a
VRF VPN Routing and Forwarding (VRF) on a PE router
towards a peering CE Customer Edge (CE) router, and on devices within a
customer network. VPN CAR SAFI is used for the distribution of
intent-aware routes from different customers received on a PE router
across the provider networks, maintaining the separation of the
customer address spaces that may overlap. The BGP CAR solution thus
enables intent-aware transport paths to be set up across a multi-
domain network that can span customer and provider network domains.
The
This document also defines two BGP CAR route types for this purpose.
The BGP CAR Type-1 NLRI (E, C) enables the generation and
distribution of multiple color-aware routes to the same destination
IP prefix for different colors. This case arises from situations
where a transport node such as a PE has a common IP address (such as
a loopback) to advertise for multiple intents. The operator intends
to use the common IP address as both the BGP next hop for service
routes and as the transport endpoint for the data plane path.
Multiple routes are needed for this same address or prefix to set up
a unique path for each intent. One example is setting up multiple
MPLS/SR-MPLS LSPs
Label Switched Paths (LSPs) for MPLS or Segment Routing over MPLS
(SR-MPLS) to an egress PE, one per intent.
The BGP CAR Type-2 NLRI (IP Prefix or E) enables the distribution of
multiple color-aware routes to a transport node for the case where
the operator specifies a unique network IP address block for a given
intent, and the transport node gets assigned a unique IP prefix or
address for each intent. An example use-case use case is SRv6 Segment Routing over
IPv6 (SRv6) per-intent locators.
These BGP CAR intent-aware paths are then used by an ingress node
(such as a PE) to steer traffic flows for service routes that need
the specific intents. Steering may be towards a destination for all
or specific traffic flows.
BGP CAR adheres to the flat routing model of BGP-IP/LU(Labeled
Unicast) but extends it to support intent-awareness, intent awareness, thereby
providing a consistent operational experience with those widely
deployed transport routing technologies.
1.1. Terminology
+=============+===================================================+
+=============+===================================================+
|
Intent (in | routing):
Any behaviors to influence routing or path |
| routing) | selection, including
any combination of the |
| | following behaviors: a)
a. Topology path selection |
| | (e.g. (e.g., minimize metric or avoid resource), b) NFV |
| |
resource)
b. Network Function Virtualization (NFV) service insertion (e.g. (e.g.,
service chain steering), |
| | c) per-hop steering)
c. Per-hop behavior (e.g. (e.g., a 5G slice). slice)
This is a |
| | more specific concept w.r.t. with respect to routing beyond best- |
| | effort,
best-effort, compared to intent as a declarative |
| | abstraction in
[RFC9315]. |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
| Color |
Color:
A non-zero 32-bit integer value associated with |
| | an intent (e.g. low-cost , low-delay, (e.g.,
low cost, low delay, or avoid |
| | some resources) as defined in [RFC9256] |
| |
Section 2.1. 2.1 of [RFC9256]. Color assignment is managed by the |
| |
operator. |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
|
Colored | service route:
An egress PE (e.g. (e.g., E2) colors its BGP service |
| Service | (e.g. (e.g., VPN) route (e.g.
(e.g., V/v) to indicate the |
| Route | intent that it requests for the
traffic bound to |
| | V/v. The color is encoded as a BGP Color |
| |
Extended-Community [RFC9012], used as per |
| | [RFC9256], or
represented by the locator part of |
| | SRv6 Service SID [RFC9252]. |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
| Color-Aware |
Color-aware path to (E2, C):
A path to forward packets towards E2 which |
| Path to | that satisfies the intent
associated with color C. |
| (E2, C) | Several technologies may provide a Color-Aware |
| | Path
color-aware path to (E2, C): C), such as SR Policy [RFC9256], IGP Flex- |
| | Algo
Flex-Algo [RFC9350], and BGP CAR [specified (as specified in this |
| | document]. |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
| Color-Aware | document).
Color-aware route (E2, C):
A distributed or signaled route that builds a |
| Route (E2, | color-aware path to
E2 for color C. |
| C) | |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
|
Service | route automated steering on color-aware path:
An ingress PE (or ASBR) E1 automatically steers |
| Route | traffic for a
C-colored service route V/v from E2 |
| Automated | onto an (E2, C) color-aware
path. If several |
| Steering on | such paths exist, a preference scheme is used to |
| Color-Aware |
select the best path (for example, IGP Flex-Algo |
| Path | is preferred over
SR Policy, and SR Policy is preferred over BGP CAR. |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
| CAR).
Color | domain:
A set of nodes which that share the same Color-to- |
| Domain | Intent color-to-intent mapping,
typically under single |
| | administration. This set can be organized
into |
| | one or multiple network domains (IGP areas/ |
| | instances areas/instances within a
single BGP AS, or multiple BGP |
| | ASes). Color-to-intent mapping on
nodes is set |
| | by configuration. Color re-mapping and filtering |
| | may
happen at color domain boundaries. Refer to |
| | [I-D.hr-spring-intentaware-routing-using-color]. |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
| [INTENT-AWARE].
Resolution | of a BGP CAR route (E, C):
An inter-domain BGP CAR route (E, C) via N is |
| of a BGP | resolved on an
intra-domain color-aware path (N, |
| CAR route | C) where N is the next hop of
the BGP CAR route. |
| (E, C) | |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
|
Resolution | In this document, and consistent versus steering:
Consistent with the |
| vs Steering | terminology used in the SR Policy document |
| | [RFC9256] Section 8, (Service
(Section 8 of [RFC9256]), in this document (service route)
steering is |
| | used to describe the mapping of the traffic for a |
| |
service route onto a BGP CAR path. In contrast, |
| | the term
resolution is preserved for the mapping |
| | of an inter-domain BGP CAR
route on an intra- |
| | domain intra-domain color-aware path. |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
| |
Service Steering: steering:
Service route maps traffic to a |
| | BGP CAR path (or other Color-Aware Path: e.g. color-
aware path, e.g., SR |
| | Policy). If a Color-Aware Path color-aware path is not
available, |
| | local policy may map to a traditional routing/TE |
| |
path (e.g. (e.g., BGP LU, RSVP-TE, IGP/LDP). The |
| | service steering
concept is agnostic to the |
| | transport technology used.
Section 3 describes |
| | the specific service steering mechanisms |
| |
leveraged for MPLS, SR-MPLS SR-MPLS, and SRv6. |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
| | Intra-Domain Resolution:
Intra-domain resolution:
BGP CAR route maps to |
| | an intra-domain color aware color-aware path (e.g. (e.g.,
SR Policy, |
| | IGP Flex-Algo, BGP CAR) or a traditional routing/TE |
| |
path (e.g. (e.g., RSVP-TE, IGP/LDP, BGP-LU). |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
|
Transport | network:
A network that comprises of multiple cooperating |
| Network | domains managed
by one or more operators, and |
| | uses routing technologies such as
IP, MPLS MPLS, and |
| | Segment Routing SR to forward packets for |
| | connectivity and other
services. In an SR |
| | deployment, the transport network is within a |
| | trust
trusted domain as per [RFC8402]. |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
|
Transport | layer:
Refers to an underlay network layer (e.g., MPLS |
| Layer | LSPs between PEs)
that gets used by an overlay or |
| | service layer (e.g., MPLS VPNs). |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
|
Transport | RR:
A BGP Route Reflector (RR) used to distribute |
| RR | transport/underlay
routes within a domain or |
| | across domains. |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
|
Service RR | RR:
A BGP Route Reflector (RR) used to distribute service/ |
| | overlay service/overlay
routes within a domain or across domains. |
+-------------+---------------------------------------------------+
Table 1
Abbreviations:
* AFI/SAFI: BGP Address-Family/Sub-Address-Family Identifiers.
*
ABR: Area Border Router
AFI: Address Family Identifier
AIGP: Accumulated IGP Metric Attribute [RFC7311].
* [RFC7311]
ASBR: Autonomous System Border Router
BGP-LU: BGP Labeled Unicast SAFI [RFC8277].
* [RFC8277]
BGP-IP: BGP IPv4/IPv6 Unicast AFI/SAFIs [RFC4271], [RFC4760].
* [RFC4271] [RFC4760]
BR: Border Router, either Router (either for an IGP Area (ABR) area (an ABR) or a BGP
Autonomous System (ASBR).
*
autonomous system (an ASBR))
Color-EC: BGP Color Extended-Community [RFC9012].
* [RFC9012]
E: Generic representation of a transport endpoint such as a PE,
ABR ABR,
or ASBR.
* ASBR
LCM-EC: BGP Local Color Mapping Extended-Community.
* Extended-Community
NLRI: Network Layer Reachability Information [RFC4271].
* [RFC4271]
P node: An intra-domain transport router.
* router
RD: Route Distinguisher
RR: BGP Route Reflector.
* Reflector
SAFI: Subsequent Address Family Identifier
TEA: Tunnel Encapsulation Attribute [RFC9012].
* [RFC9012]
V/v, W/w: Generic representations of a service route (indicating
prefix/masklength),
prefix/mask length), regardless of AFI/SAFI or actual NLRI
encoding.
encoding
1.2. Illustration
Here is a brief illustration of the salient properties of the BGP CAR
solution.
+-------------+ +-------------+ +-------------+
| | | | | | V/v with C1
|----+ |------| |------| +----|/
| E1 | | | | | | E2 |\
|----+ | | | | +----| W/w with C2
| |------| |------| |
| Domain 1 | | Domain 2 | | Domain 3 |
+-------------+ +-------------+ +-------------+
Figure 1: BGP CAR Solution Illustration
All the nodes are part of an inter-domain network under a single
authority and with a consistent color-to-intent mapping:
* C1 is mapped to "low-delay"
- Flex-Algo FA1 is mapped to "low delay" delay", and hence to C1
* C2 is mapped to "low-delay and avoid resource R"
- Flex-Algo FA2 is mapped to "low delay and avoid resource R" R",
and hence to C2
E1 receives two service routes from E2:
* V/v with BGP Color-EC C1
* W/w with BGP Color-EC C2
E1 has the following color-aware paths:
* (E2, C1) provided by BGP CAR with the following per-domain
support:
- Domain1: Domain 1: over IGP FA1
- Domain2: Domain 2: over SR Policy bound to color C1
- Domain3: Domain 3: over IGP FA1
* (E2, C2) provided by SR Policy
E1 automatically steers traffic for the received service routes as
follows:
* V/v via (E2, C1) provided by BGP CAR
* W/w via (E2, C2) provided by SR Policy
Illustrated Properties: properties:
* Leverage of the BGP Color-EC
- The service routes are colored with widely used BGP Color
Extended-Community [RFC9012] to request intent
* (E, C) Automated Steering automated steering
- V/v and W/w are automatically steered on the appropriate color-
aware path
* Seamless co-existence coexistence of BGP CAR and SR Policy
- V/v is steered on BGP CAR color-aware path
- W/w is steered on SR Policy color-aware path
* Seamless interworking of BGP CAR and SR Policy
- V/v is steered on a BGP CAR color-aware path that is itself
resolved within domain 2 onto an SR Policy bound to the color
of V/v
Other properties:
* MPLS data-plane: with 300k PE's PEs and 5 colors, the BGP CAR solution
ensures that no single node needs to support a data-plane scaling
in the order of Remote PE * C (Section 5). This would otherwise
exceed the MPLS data-plane.
* Control-Plane: Control-plane: a node should not install a (E, C) path if it's not
participating in that color-aware path.
* Incongruent Color-Intent color-intent mapping: the solution supports the
signaling of a BGP CAR route across different color domains. domains
(Section 2.8) 2.8).
The key benefits of this model are:
* leverage Leverage of the BGP Color-EC [RFC9012] to color service routes
* the The definition of the automated service steering: a C-colored
service route V/v from E2 is steered onto a color-aware path (E2,
C)
* the The definition of the data model of a BGP CAR path: (E, C)
- natural Natural extension of BGP IP/LU data model (E)
- consistent Consistent with SR Policy data model
* the The definition of the recursive resolution of a BGP CAR route: a
BGP CAR (E2, C) route via N is resolved onto the color-aware path
(N, C) C), which may itself be provided by BGP CAR or via another
color-aware routing solution (e.g., SR Policy, IGP Flex-Algo). Flex-Algo)
* Native support for multiple transport encapsulations (e.g., MPLS,
SR, SRv6, IP)
1.3. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. BGP CAR SAFI
2.1. Data Model
The BGP CAR data model is:
*
NLRI Key: key: Falls into two categories, categories to accommodate the use-cases use cases
described in the introduction:
-
Type-1: Key is IP Prefix and Color (E, C). Color in NLRI key
distinguishes a color-aware route for a common IP prefix, one
per intent. Color also indicates the intent associated with
the route.
-
Type-2: Key is IP Prefix (E). The unique IP prefix assigned for
an intent (i.e, IP Prefix == Intent intent or Color) distinguishes the
color-aware route. Color is not needed in NLRI key as a
distinguisher.
*
NLRI non-key encapsulation data: Data such as MPLS label stack,
Label Index Index, and SRv6 SID list associated with NLRI. Contained in
TLVs as described in Section 2.9.2
* 2.9.2.
BGP Next Hop.
* next hop.
AIGP Metric metric [RFC7311]: accumulates color/intent specific Accumulates a metric value specific to color/
intent for a CAR route across multiple BGP hops.
*
Local-Color-Mapping Extended-Community (LCM-EC): Optional non-zero
32-bit Color value used to represent the intent associated with a
CAR route:
-
* when the CAR route propagates between different color domains.
-
* when the CAR route has a unique IP prefix for an intent.
*
BGP Color Extended-Community (Color-EC) [RFC9012]: Optional non-
zero non-zero
32-bit Color value used to represent the intent associated with
the BGP CAR next hop. It is used as per [RFC9256] for automated
route resolution, when intent/color used for the next hop is
different than the CAR route's intent/color.
The sections below describe the data model in detail. The sections
that describe the protocol processing for CAR SAFI generally apply
consistently to both route types (for instance, any operation based
on color). The examples use (E, C) for simplicity.
2.2. Extensible Encoding
Extensible encoding is provided by:
*
NLRI Type field: This provides extensibility to add new NLRI formats
for new route-types. route types.
NLRI (Route) Types (route) types other than Type-1 (E, C) and Type-2 (E) are
outside the scope of this document.
*
Key length Length field: This specifies the key length. It allows new NLRI
types to be handled opaquely, which permits transitivity of new
route types through BGP speakers such as Route Reflectors.
* Reflectors (RRs).
TLV-based encoding of non-key part of NLRI: This allows the
inclusion of additional non-key fields for a prefix to support
different types of transport simultaneously with efficient BGP
update packing (Section 2.9).
*
AIGP Attribute attribute: This provides extensibility via TLVs, enabling
definition of additional metric semantics for a color as needed
for an intent.
2.3. BGP CAR Route Origination
A BGP CAR route may be originated locally (e.g., loopback) or through
redistribution of an (E, C) color-aware path provided by another
routing solution: e.g., solution (e.g., SR Policy, IGP Flex-Algo, RSVP-TE, BGP-LU
[RFC8277].
[RFC8277]).
2.4. BGP CAR Route Validation
A BGP CAR path (E, C) via next hop N with encapsulation T is valid if
color-aware path (N, C) exists with encapsulation T available in
data-plane.
A local policy may customize the validation process:
* The color constraint in the first check may be relaxed. If N is
reachable via alternate color(s) or in the default routing table,
the route may be considered valid.
* The data-plane availability constraint of T may be relaxed to use
an alternate encapsulation.
* A performance-measurement verification may be added to ensure that
the intent associated with C is met (e.g. (e.g., delay < bound).
A path that is not valid MUST NOT be considered for BGP best path
selection.
2.5. BGP CAR Route Resolution
A BGP color-aware route (E2, C1) with next hop N is automatically
resolved over a color-aware route (N, C1) by default. The color-
aware route (N, C1) is provided by color aware color-aware mechanisms such as IGP
Flex-Algo [RFC9350], SR policy [RFC9256] Section 2.2, (Section 2.2 of [RFC9256]), or
recursively by BGP CAR. When multiple producers of (N, C1) are
available, the default preference is: IGP Flex-Algo, SR Policy, BGP
CAR.
Local policy SHOULD provide additional control:
* A BGP color-aware route (E2, C1) with next hop N may be resolved
over a color-aware route (N, C2): i.e., C2) (i.e., the local policy maps the
resolution of C1 over a different color C2. C2).
- For example, in a domain where resource R is known to not be
present, the inter-domain intent C1="low delay and avoid R" may
be resolved over an intra-domain path of intent C2="low delay".
- Another example is: if no (N, C1) path is available and the
user has allowed resolution to fallback to a C2 path.
* Route resolution may be driven by an egress node. In an SRv6
domain, an egress node selects and advertises an SRv6 SID from its
locator for intent C1, with a BGP CAR route. In such a case, the
ingress node resolves the received SRv6 SID over an IPv6 route for
the intent-aware locator of the egress node for C1 or a summary
route that covers the locator. This summary route may be provided
by SRv6 Flex Algo or BGP CAR IP Prefix route itself (e.g.,
Appendix C.2).
* Local policy may map the CAR route to traditional mechanisms that
are unaware of color or that provide best-effort, such as RSVP-TE,
IGP/LDP, BGP LU/IP (e.g., Appendix A.3.2) for brownfield
scenarios.
Route resolution via a different color C2 can be automated by
attaching BGP Color-EC C2 to CAR route (E2, C1), leveraging Automated automated
steering as described in Section 8.4 of Segment "Segment Routing Policy
Architecture
Architecture" [RFC9256] for BGP CAR routes. This mechanism is
illustrated in Appendix B.2. This mechanism SHOULD be supported.
For CAR route resolution, Color-EC color if present takes precedence
over the route's intent color (LCM-EC if present (Section 2.9.5), or
else NLRI color).
Local policy takes precedence over the color based color-based automated
resolution specified above.
The color-aware route (N, C1) may be provided by BGP CAR itself in a
hierarchical transport routing design. In such cases, based on the
procedures described above, recursive resolution may occur over the
same or different CAR route type. Section 7.1.2 describes a scenario
where CAR (E, C) route resolves over CAR IP Prefix route.
CAR IP Prefix route is allowed to be without color for best-effort.
In this case, resolution is based on BGP next hop N, or when present,
a best-effort SRv6 SID advertised by node N.
A BGP CAR route may recursively resolve over a BGP route that carries
a TEA and follows Section 6 of [RFC9012] for validation. In this
case, the procedures of section Section 8 of [RFC9012] apply to BGP CAR
routes, using color precedence as specified above for resolution.
The procedures of [RFC9012] [RFC9012], Section 6 6, also apply to BGP CAR routes
(AFI/SAFI = 1/83 or 2/83). For instance, a BGP CAR BR may advertise
a BGP CAR route to an ingress BR or PE with a specific BGP next hop
per color, with a TEA or Tunnel Encapsulation EC, as per Section 6 of
[RFC9012].
BGP CAR resolution in one network domain is independent of resolution
in another domain.
2.6. AIGP Metric Computation
The Accumulated IGP (AIGP) Metric Attribute [RFC7311] is updated as
the BGP CAR route propagates across the network.
The value set (or appropriately incremented) in the AIGP TLV
corresponds to the metric associated with the underlying intent of
the color. For example, when the color is associated with a low-
latency path, the metric value is set based on the delay metric.
Information regarding the metric type used by the underlying intra-
domain mechanism can also be used to set the metric value.
If BGP CAR routes traverse across a discontinuity in the transport
path for a given intent, a penalty is added in accumulated IGP the AIGP metric (value
set by user policy). For This could occur, for instance, when color C1
path is not available, and route resolves via color C2 path (See (see
Appendix A.3 for an example).
AIGP metric computation is recursive.
To avoid continuous IGP metric changes causing end to end end-to-end BGP CAR
route churn, an implementation should provide thresholds to trigger
AIGP update. updates.
Additional AIGP extensions may be defined to signal state for
specific use-cases: use cases such as Maximum SID-Depth SID Depth (MSD) along the BGP CAR
route
advertisement, Minimum advertisement and minimum MTU along the BGP CAR route
advertisement. This is out of scope for this document.
2.7. Native MultiPath Multipath Capability
The (E, C) route definition inherently provides availability of
redundant paths at every BGP hop identical to BGP-LU or BGP IP. For
instance, BGP CAR routes originated by two or more egress ABRs in a
domain are advertised as multiple paths to ingress ABRs in the
domain, where they become equal-cost or primary-backup paths. A
failure of an egress ABR is detected and handled by ingress ABRs
locally within the domain for faster convergence, without any
necessity to propagate the event to upstream nodes for traffic
restoration.
BGP ADD-PATH [RFC7911] SHOULD be enabled for BGP CAR to signal
multiple next hops through a transport RR.
2.8. BGP CAR Signaling through different Through Different Color Domains
[Color Domain 1 A]-----[B Color Domain 2 E2]
[C1=low-delay ] [C2=low-delay ]
Let us assume a BGP CAR route (E2, C2) is signaled from B to A, two
border routers of respectively domain Domain 2 and domain 1. Domain 1, respectively. Let us assume
that these two domains do not share the same color-to-intent mapping
(i.e., they belong to different color domains). Low-delay in domain Domain
2 is color C2, while it is C1 in domain Domain 1 (C1 <> C2).
It is not expected to be a typical scenario to have an underlay
transport path (e.g., an MPLS LSP) extend across different color
domains. However, the BGP CAR solution seamlessly supports this rare
scenario while maintaining the separation and independence of the
administrative authority in different color domains.
The solution works as described below:
* Within domain Domain 2, the BGP CAR route is (E2, C2) via E2.
* B signals to A the BGP CAR route as (E2, C2) via B with Local-
Color-Mapping-Extended-Community (LCM-EC) of color C2.
* A is aware of the intent-to-color mapping within domain Domain 2 ("low-
delay" in domain Domain 2 is C2), as per typical coordination that exists
between operators of peering domains.
* A maps C2 in LCM-EC to C1 and signals within domain Domain 1 the received
BGP CAR route as (E2, C2) via A with LCM-EC(C1). LCM-EC (C1).
* The nodes within the receiving domain Domain 1 use the local color
encoded in the LCM-EC for next-hop resolution and service
steering.
The following procedures apply at a color domain boundary for BGP CAR
routes, performed by route policy at the sending and receiving peer:
* Use local policy to control which routes are advertised to or
accepted from a peer in a different color domain.
* Attach LCM-EC if not present with the route. If LCM-EC is
present, then update the value to re-map the color as needed.
- This function may be done by the advertising BGP speaker or the
receiving BGP speaker as determined by the operator peering
agreement, and indicated by local policy on the BGP peers.
These procedures apply to both CAR route types, in addition to all
procedures specified in earlier sections. LCM-EC is described in
Section 2.9.5.
Salient properties:
* The NLRI never changes, even though the color-to-intent mapping
changes
changes.
* E is globally unique, which makes E-C in that order unique unique.
* In typical expected cases, the color of the NLRI is used for
resolution and steering steering.
* In the rare case of color incongruence, the local color encoded in
LCM-EC takes precedence precedence.
Operational consideratons considerations are in Section 11. Further illustrations
are provided in Appendix B.
2.9. Format and Encoding
BGP CAR leverages BGP multi-protocol extensions [RFC4760] and uses
the MP_REACH_NLRI and MP_UNREACH_NLRI attributes for route updates
within SAFI value 83 along with AFI 1 for IPv4 prefixes and AFI 2 for
IPv6 prefixes.
BGP speakers MUST use the BGP Capabilities Advertisement to ensure
support for processing of BGP CAR updates. This is done as specified
in [RFC4760], by using capability code 1 (multi-protocol BGP), with
AFI 1 and 2 (as required) and SAFI 83.
The Next Hop network address field in the MP_REACH_NLRI may either be
an IPv4 address or an IPv6 address, independent of AFI. If the next
hop length is 4, then the next hop is an IPv4 address. The next hop
length may be 16 or 32 for an IPv6 next hop address, set as per
section
Section 3 of [RFC2545]. Processing of the Next Hop field is governed
by standard BGP procedures as described in section Section 3 of [RFC4760].
The sub-sections below specify the generic encoding of the BGP CAR
NLRI and non-key TLV fields fields, followed by the encoding for specific
NLRI types introduced in this document.
2.9.1. BGP CAR SAFI NLRI Format
The generic format for the BGP CAR SAFI NLRI is shown below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NLRI Length | Key Length | NLRI Type | //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ //
| Type-specific Type-Specific Key Fields //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type-specific Type-Specific Non-Key TLV Fields (if applicable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
*
NLRI Length: 1 octet 1-octet field that indicates the length in octets of
the NLRI excluding the NLRI Length field itself.
*
Key Length: 1 octet 1-octet field that indicates the length in octets of the
NLRI type-specific key fields. Key length MUST be at least 2 less
than the NLRI length.
*
NLRI Type: 1 octet 1-octet field that indicates the type of the BGP CAR
NLRI.
*
Type-Specific Key Fields: The exact definition of these fields
depends on the NLRI type. They have length indicated by the Key
Length.
*
Type-Specific Non-Key TLV Fields: The fields are optional and can
carry one or more non-key TLVs (of different types) depending on
the NLRI type. The NLRI definition allows for encoding of
specific non-key information associated with the route as part of
the NLRI for efficient packing of BGP updates.
The non-key TLVs portion of the NLRI MUST be omitted while carrying
it within the MP_UNREACH_NLRI when withdrawing the route
advertisement.
Error handling for CAR SAFI NLRI and non-key TLVs is described in
Section 2.11.
Benefits
The benefits of CAR NLRI design: design are:
* The indication of the key length enables BGP Speakers speakers to determine
the key portion of the NLRI and use it along with the NLRI Type
field in an opaque manner for the handling of unknown or
unsupported NLRI types. This can help deployed Route Reflectors
(RR) to propagate NLRI types introduced in the future in a
transparent manner.
* The key length also helps error handling be more resilient and
minimally disruptive. The use of key length in error handling is
described in Section 2.11.
* The ability of a route (NLRI) to carry more than one non-key TLV
(of different types) provides significant benefits such as
signaling multiple encapsulations simultaneously for the same
route, each with a different value (label/SID etc). (label/SID, etc.). This
enables simpler, simpler and efficient migrations with low overhead :
* overhead:
- avoids the need for duplicate routes to signal different
encapsulations
*
- avoids the need for separate control planes for distribution
*
- preserves update packing (e.g. (e.g., Appendix D)
2.9.2. Type-Specific Non-Key TLV Format
The generic format for Non-Key TLVs is shown below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Value (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
*
Type: 1 octet that contains the type code and flags. It is encoded
as shown below:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|R|T| Type code |
+-+-+-+-+-+-+-+-+
where:
-
R: Bit is reserved and MUST be set to 0 and ignored on receive.
-
T: Transitive bit, applicable to speakers that change the BGP CAR
next hop.
o
* The T bit is set to indicate TLV is transitive. An
unrecognized transitive TLV MUST be propagated by a speaker
that changes the next hop.
o
* The T bit is unset to indicate TLV is non-transitive. An
unrecognized non-transitive TLV MUST NOT be propagated by a
speaker that changes the next hop.
A speaker that does not change the next hop SHOULD propagate
all received TLVs.
-
Type code: Remaining 6 bits contain the type of the TLV.
*
Length: 1 octet 1-octet field that contains the length of the value portion
of the non-key TLV in terms of octets.
*
Value: variable length Variable-length field as indicated by the length Length field and to
be interpreted as per the type Type field.
The following sub-sections specify non-key TLVs. Each NLRI type MUST
list the TLVs that can be associated with it.
2.9.2.1. Label TLV
The Label TLV is used for the advertisement of CAR routes along with
their MPLS labels and labels. It has the following format as per Section 2.9.2:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|T| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Followed
It is followed by one (or more) Labels encoded as below:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label |Rsrv |S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type :
Type: Type code is 1. The T bit MUST be unset.
*
Length: In octets. Length is in octets, variable, and MUST be a multiple of 3.
*
Label Information: multiples Multiples of 3 octet 3-octet fields to convey the MPLS
label(s) associated with the advertised CAR route. It is used for
encoding a single label or a stack of labels for usage as
described in [RFC8277]. Number The number of labels is derived from length the
Length field. The 3-bit Rsrv field and the 1-bit S field SHOULD
be set to zero on transmission and MUST be ignored on reception.
If a BGP transport CAR speaker sets itself as the next hop while
propagating a CAR route, it allocates a local label for the type type-
specific key, and updates the value in this TLV. It also MUST
program a label cross-connect that would result in the label swap
operation for the incoming label that it advertises with the label
received from its best-path router(s).
2.9.2.2. Label Index TLV
The Label Index TLV is used for the advertisement of Segment Routing
over MPLS (SR-MPLS) Segment Identifier (SID) [RFC8402] information
associated with the labeled CAR routes and routes. It has the following format
as per Section 2.9.2:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|T| Type | Length | Reserved | Flags ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | Label Index ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ |
+-+-+-+-+-+-+-+-+
where:
* Type :
Type: Type code is 2. The T bit MUST be set.
*
Length: In octets. Length is in octets and is 7.
*
Reserved: 1 octet 1-octet field that MUST be set to 0 and ignored on
receipt.
*
Flags: 2 octet 2-octet field that's defined as per the Flags field of the
Label Index TLV of the BGP Prefix-SID Attribute ([RFC8669] section
3.1).
* attribute (Section 3.1 of
[RFC8669]).
Label Index: 4 octet 4-octet field that's defined as per the Label Index
field of the Label Index TLV of the BGP Prefix-SID Attribute
([RFC8669] section 3.1). attribute
(Section 3.1 of [RFC8669]).
This TLV provides the equivalent functionality as the Label Index TLV
of [RFC8669] for Transport CAR route in SR-MPLS deployments. When a
speaker allocates a local label for a received CAR route as per
Section 2.9.2.1, it SHOULD use the received Label Index as a hint
using procedures as specified in [RFC8669] [RFC8669], Section 4.
The Label Index TLV provides much better packing efficiency by
carrying the Label Index in NLRI instead of in the BGP Prefix-SID
Attribute
attribute (Appendix D).
The Label Index TLV MUST NOT be carried in the Prefix-SID attribute
for BGP CAR routes. If a speaker receives a CAR route with the Label
Index TLV in the Prefix-SID attribute, it SHOULD ignore it. The BGP
Prefix-SID Attribute attribute SHOULD NOT be sent with the labeled CAR routes
if the attribute is being used only to convey the Label Index TLV.
2.9.2.3. SRv6 SID TLV
BGP Transport CAR can be also used to setup set up end-to-end color-aware
connectivity using Segment Routing over IPv6 (SRv6) [RFC8402].
[RFC8986] specifies the SRv6 Endpoint behaviors (e.g. (e.g., End PSP)
Penultimate Segment Pop (PSP)), which can be leveraged for BGP CAR
with SRv6. The SRv6 SID TLV is used for the advertisement of CAR
routes along with their SRv6 SIDs and SIDs. It has the following format as
per Section 2.9.2:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|T| Type | Length | SRv6 SID Info (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type :
Type: Type code is 3. The T bit MUST be unset.
*
Length: In octets. Length is in octets, variable, and MUST be either less than
or equal to 16, or be a multiple of 16.
*
SRv6 SID Information: field Field of size as indicated by the length that
either carries the SRv6 SID(s) for the advertised CAR route as one
of the following:
-
* A single 128-bit SRv6 SID or an ordered list of 128-bit SRv6
SIDs.
-
* A transposed portion (refer to [RFC9252]) of the SRv6 SID that
MUST be of size in multiples of one octet and less than 16.
BGP CAR SRv6 SID TLV definitions provide the following benefits:
* Native The native encoding of SIDs avoids robustness issue issues caused by the
overloading of MPLS label fields.
* Simple The simple encoding to signal Unique SIDs (non-transposition),
maintaining (non-transposition)
maintains BGP update prefix packing.
* Highly The highly efficient transposition scheme (12-14 bytes saved per
NLRI),
NLRI) also maintaining maintains BGP update prefix packing.
The BGP CAR route update for SRv6 encapsulation MUST include the BGP
Prefix-SID attribute along with the SRv6 L3 Service TLV carrying the
SRv6 SID information as specified in [RFC9252]. When using the
transposition scheme of encoding for packing efficiency of BGP
updates [RFC9252], the transposed part of the SID is carried in the
SRv6 SID TLV and is not limited by MPLS label field size.
If a BGP transport CAR speaker sets itself as the next hop while
propagating a CAR route and allocates an SRv6 SID that maps to the
received SRv6 SID, it updates the value in this TLV.
Received MPLS information can map to SRv6 and vice versa.
[I-D.ietf-spring-srv6-mpls-interworking]
[SRv6-INTERWORK] describes MPLS and SRv6 interworking procedures and
an extension to BGP CAR routes.
2.9.3. Color-Aware Route (E, C) NLRI Type
The Color-Aware Route NLRI Type is used for the advertisement of BGP
CAR color-aware routes (E, C) and C). It has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NLRI Length | Key Length | NLRI Type |Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Prefix (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Followed
It is followed by optional Non-Key TLVs encoded as per Section 2.9.2
where:
* 2.9.2.
Where:
NLRI Length: variable
* Variable.
Key Length: variable. Variable. It indicates the total length comprised of
the Prefix Length field, IP Prefix field, and the Color field, as
described below. For IPv4 (AFI=1), the minimum length is 5 and
the maximum length is 9. For IPv6 (AFI=2), the minimum length is
5 and the maximum length is 21.
*
NLRI Type: 1
* 1.
Type-Specific Key Fields: These are as below
- seen below:
Prefix Length: 1 octet 1-octet field that carries the length of prefix in
bits. Length MUST be less than or equal to 32 for IPv4 (AFI=1)
and less than or equal to 128 for IPv6 (AFI=2).
-
IP Prefix: IPv4 or IPv6 prefix (based on the AFI). A variable variable-
size field that contains the most significant octets of the
prefix. The format of this field for an IPv4 prefix is:
* 0 octet for prefix length 0, 0
* 1 octet for prefix length 1 to 8, 8
* 2 octets for prefix length 9 to 16, 16
* 3 octets for prefix length 17 up to 24, 24
* 4 octets for prefix length 25 up to 32.
- 32
The format for this field for an IPv6 address follows the same
pattern for prefix lengths of 1-128 (octets 1-16).
-
The last octet has enough trailing bits to make the end of the
field fall on an octet boundary. Note that the value of the
trailing bits MUST be set to zero. The size of the field MUST
be less than or equal to 4 for IPv4 (AFI=1) and less than or
equal to 16 for IPv6 (AFI=2).
-
Color: 4 octets that contains contain non-zero color value associated with
the prefix.
*
Type-Specific Non-Key TLVs: The Label TLV, Label Index TLV TLV, and SRv6
SID TLV (Section 2.9.2) may be associated with the Color-aware
route NLRI type.
The prefix is unique across the administrative domains where BGP
transport CAR is deployed. It is possible that the same prefix is
originated by multiple BGP CAR speakers in the case of anycast
addressing or multi-homing. multihoming.
The Color is introduced to enable multiple route advertisements for
the same prefix. The color is associated with an intent (e.g. (e.g., low-
latency) in originator color-domain. color domain.
2.9.4. IP Prefix (E) NLRI Type
The IP Prefix Route NLRI Type is used for the advertisement of BGP
CAR IP Prefix routes (E) and (E). It has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NLRI Length | Key Length | NLRI Type |Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Prefix (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Followed
It is followed by optional Non-Key TLVs encoded as per Section 2.9.2
where:
* 2.9.2.
Where:
NLRI Length: variable
* Variable.
Key Length: variable. Variable. It indicates the total length comprised of
the Prefix Length field and IP Prefix field as described below.
For IPv4 (AFI=1), the minimum length is 1 and the maximum length
is 5. For IPv6 (AFI=2), the minimum length is 1 and the maximum
length is 17.
*
NLRI Type: 2.
*
Type-Specific Key Fields: These are as below
- seen below:
Prefix Length: 1 octet 1-octet field that carries the length of prefix in
bits. Length MUST be less than or equal to 32 for IPv4 (AFI=1)
and less than or equal to 128 for IPv6 (AFI=2).
-
IP Prefix: IPv4 or IPv6 prefix (based on the AFI). A variable variable-
size field that contains the most significant octets of the
prefix. The format of this field for an IPv4 prefix is:
* 0 octet for prefix length 0, 0
* 1 octet for prefix length 1 to 8, 8
* 2 octets for prefix length 9 to 16, 16
* 3 octets for prefix length 17 up to 24, 24
* 4 octets for prefix length 25 up to 32.
- 32
The format for this field for an IPv6 address follows the same
pattern for prefix lengths of 1-128 (octets 1-16).
-
The last octet has enough trailing bits to make the end of the
field fall on an octet boundary. Note that the value of the
trailing bits MUST be set to zero. The size of the field MUST
be less than or equal to 4 for IPv4 (AFI=1) and less than or
equal to 16 for IPv6 (AFI=2).
*
Type-Specific Non-Key TLVs: The Label TLV, Label Index TLV TLV, and SRv6
SID TLV (Section 2.9.2) may be associated with the IP Prefix NLRI
type.
2.9.5. Local-Color-Mapping (LCM) Extended-Community
This document defines a new BGP Extended-Community called "LCM". The
LCM is a Transitive Opaque Extended-Community with the following
encoding:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x3 | Sub-Type=0x1b | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
*
Type: 0x3.
*
Sub-Type: 0x1b.
*
Reserved: 2 octet of 2-octet reserved field that MUST be set to zero on
transmission and ignored on reception.
*
Color: 4-octet field that carries the non-zero 32-bit color value.
When a CAR route crosses the originator's color domain boundary, LCM-
EC is added or updated, as specified in Section 2.8. LCM-EC conveys
the local color mapping for the intent (e.g. (e.g., low latency) in other
(transit or destination) color domains.
For CAR IP Prefix routes, LCM-EC may also be added in the originator
color domain to indicate the color associated with the IP prefix.
An implementation SHOULD NOT send more than one instance of the LCM-
EC. However, if more than one instance is received, an
implementation MUST disregard all instances other than the one with
the numerically highest value.
If a node receives multiple BGP CAR routes (paths) for a given
destination endpoint and color that have different LCM values, it is
a misconfiguration in color re-mapping for one of the routes.
In this case, the LCM from the selected BGP best path SHOULD be
chosen to be installed into the routing table.
A warning message SHOULD also be logged for further operator
intervention.
If present, LCM-EC contains the intent of a BGP CAR route. LCM-EC
Color is used instead of the Color in CAR route NLRI for procedures
described in earlier sections such as route validation (Section 2.4),
route resolution (Section 2.5), AIGP calculation (Section 2.6) and
steering (Section 3).
The LCM-EC MAY be used for filtering of BGP CAR routes and/or for
applying routing policies on the intent, when present.
2.10. LCM-EC and BGP Color-EC usage Usage
There are 2 distinct requirements to be supported as stated in
[I-D.hr-spring-intentaware-routing-using-color]:
[INTENT-AWARE]:
1. Domains with different intent granularity (section 6.3.1.9) (Section 6.3.1.9 of
[INTENT-AWARE])
2. Network domains under different administration, i.e., administration (i.e., color
domains (section 6.3.1.10)
domains; see Section 6.3.1.10 of [INTENT-AWARE])
Requirement 1 is the case where within the same administrative or
color domain, BGP CAR routes for N end-to-end intents may need to
traverse across an intermediate transit domain where only M intents
are available, N >= M. For example, consider a multi-domain network
is designed as Access-Core-Access. The core may have the most
granular N intents, whereas the access only has fewer M intents. So,
Therefore, the BGP next-hop resolution for a CAR route in the access
domain must be via a color-aware path for one of these M intents. As
the procedures in Section 2.5 describe, and the example in
Appendix B.2 illustrates, BGP Color-EC is used to automate the CAR
route resolution in this case.
For requirement 2, where CAR routes traverse across different color
domains, LCM-EC is used to carry the local color mapping for the NLRI
color in other color domains. The related procedures are described
in Section 2.8, and an example is given in Appendix B.3.
Both LCM-EC and BGP Color-EC may be present at the same time with a
BGP CAR route. For example, a BGP CAR route (E, C1) from color
domain D1, with LCM-EC C2 in color domain D2, may also carry Color-EC
C3 and next hop N in a transit network domain within D2 where C2 is
being resolved via an available intra-domain intent C3 (See (see the
detailed example in the combination of Appendix Appendices B.2 and
Appendix B.3).
In this case, as described in Section 2.5, the default order of
processing for resolution in the presence of LCM-EC is local policy,
then BGP Color-EC color, and finally LCM-EC color.
2.11. Error Handling
The error handling actions as described in [RFC7606] are applicable
for the handling of BGP update messages for BGP CAR SAFI. In
general, as indicated in [RFC7606], the goal is to minimize the
disruption of a session reset or 'AFI/SAFI disable' to the extent
possible.
When the error determined allows for the router to skip the malformed
NLRI(s) and continue processing of the rest of the update message,
then it MUST handle such malformed NLRIs as 'Treat-as-withdraw'. 'treat-as-withdraw'. In
other cases, where the error in the NLRI encoding results in the
inability to process the BGP update message, then the router SHOULD
handle such malformed NLRIs as 'AFI/SAFI disable' when other AFI/SAFI
besides BGP CAR are being advertised over the same session.
Alternately, the router MUST perform 'session reset' when the session
is only being used for BGP CAR SAFI.
The CAR NLRI definition encodes NLRI length and key length
explicitly. The NLRI length MUST be relied upon to enable the
beginning of the next NLRI field to be located. Key length MUST be
relied upon to extract the key and perform 'treat-as-withdraw' for
malformed information.
A sender MUST ensure that the NLRI and key lengths are the number of
actual bytes encoded in the NLRI and key fields fields, respectively,
regardless of content being encoded.
Given NLRI length and Key length MUST be valid, failures in the
following checks result in 'AFI/SAFI disable' or 'session reset':
* Minimum NLRI length (must be atleast at least 2, as key length and NLRI
type are required fields).
* Key Length MUST be at least two less than NLRI Length.
NLRI Type specific type-specific error handling:
* By default, a speaker SHOULD discard an unrecognized or
unsupported NLRI type and move to the next NLRI.
* Key length and key errors of a known NLRI type SHOULD result in
the discard of NLRI similar to an unrecognized NLRI type. (This
MUST be logged for trouble shooting). shooting.)
Transparent propagation of unrecognized NLRI type:
* Key length allows unrecognized route types to transit through the
RR transparently without a software upgrade. The RR receiving
unrecognized route types does not need to interpret the key
portion of an NLRI and handles the NLRI as an opaque value of a
specific length. An implementation SHOULD provide configuration
that controls the RR unrecognized route type propagation behavior
and behavior,
possibly at the granularity of route type values allowed. This
configuration option gives the operator the ability to allow
specific route types to be transparently passed through RRs based
on client speaker support.
* In such a case RR case, the RRs may reflect NLRIs with NLRI type specific type-specific
key length and field errors. Clients of such an RR that consume
the route for installation will perform the key error handling of
known NLRI type or discard the unrecognized type. This prevents
propagation of routes with NLRI errors any further in network.
Type-Specific
Type-specific Non-Key TLV handling:
* Either the length of a TLV would cause the NLRI length to be
exceeded when parsing the TLV, or fewer than 2 bytes remain when
beginning to parse the TLV. In either of these cases, an error
condition exists exists, and the 'treat-as-withdraw' approach MUST be
used.
* Type specific Type-specific length constraints should be verified. The TLV MUST
be discarded if there is an error. When discarded, an error may
be logged for further analysis.
* If multiple instances of same type are encountered, all but the
first instance MUST be discarded. When discarded, an error may be
logged for further analysis.
* If a speaker that performs encapsulation to the BGP next hop does
not receive at least one recognized forwarding information TLV
with the T bit unset (such as label or SRv6 SID), such NLRI is
considered invalid and not eligible for best path selection.
Treat-as-withdraw
'Treat-as-withdraw' may be used, though it is recommended to keep
the NLRI for debugging purposes.
3. Service Route Automated Steering on Color-Aware Path Paths
An ingress PE (or ASBR) E1 automatically steers a C-colored service
route V/v from E2 onto an (E2, C) color-aware path, as illustrated in
(Section 1.2).
Section 1.2. If several such paths exist, a preference scheme is
used to select the best path. The default preference scheme is IGP
Flex-Algo first, then SR Policy, followed by BGP CAR. A
configuration option may be used to adjust the default preference
scheme.
An egress PE may express its intent that traffic should be steered a
certain way through the transport layer by including the BGP Color-EC
[RFC9012] with the relevant service routes. An ingress PE steers
service traffic over a CAR (E, C) route using the service route's
next hop and BGP Color-EC.
This is consistent with the automated service route steering on SR
Policy (a routing solution providing color-aware path) paths) defined in
[RFC9256]. All the steering variations described in [RFC9256] are
applicable to BGP CAR color-aware path: paths: on-demand steering, per-
destination, per-flow,
destination steering, per-flow steering, and color-only steering.
For brevity, please refer to [RFC9256] Section 8. 8 of [RFC9256].
Appendix A provides illustrations of service route automated steering
over BGP CAR (E, C) routes.
An egress PE may express its intent that traffic should be steered a
certain way through the transport layer by allocating the SRv6
Service SID from a routed intent-aware locator prefix (Section 3.3 of
[RFC8986]). Steering at an ingress PE is via resolution of the
Service SID over a CAR Type-2 IP Prefix route. Service Steering steering over
BGP CAR SRv6 transport is described in Section 7.
Service steering via BGP CAR routes is applicable to any BGP SAFI,
including SAFIs for IPv4/IPv6 (SAFI 1), L3VPN (SAFI 128), PW, pseudowire
(PW), EVPN (SAFI 70), FlowSpec, and BGP-LU (SAFI 4).
4. Filtering
PE
PEs and BRs may support filtering of CAR routes. For instance, the
filtering may only accept routes of locally configured colors.
Techniques such as RT-Constrain RT Constrain [RFC4684] may also be applied to the
CAR SAFI, where Route Target (RT) Extended-Communities [RFC4360] can
be used to constrain distribution and automate filtering of CAR
routes. RT assignment may be via user policy, policy; for example example, an RT
value can be assigned to all routes of a specific color.
A PE may support on-demand installation of a CAR route based on the
presence of a service route whose next-hop next hop resolves via the CAR
route.
Similarly, a PE may dynamically subscribe to receive individual CAR
routes from upstream routers or route-reflectors Route Reflectors (RRs) to limit the
routes that it needs to learn. On-demand subscription and automated
filtering procedures for individual CAR routes are outside the scope
of this document.
5. Scaling
This section analyses analyzes the key scale requirement of
[I-D.hr-spring-intentaware-routing-using-color], [INTENT-AWARE],
specifically:
* No intermediate node data-plane should need to scale to (Colors *
PEs).
* No node should learn and install a BGP CAR route to (E, C) if it
does not install a Colored colored service route to E.
While the requirements and design principles generally apply to any
transport, the logical analysis based on the network design in this
section focuses on MPLS / SR-MPLS MPLS/SR-MPLS transport since the scaling
constraints are specifically relevant to these technologies. BGP CAR
SAFI is used here, but the considerations can apply to [RFC8277] or
[RFC8669] used with MPLS/SR-MPLS.
Two key principles used to address the scaling requirements are a
hierarchical network and routing design, and on-demand route
subscription and filtering.
Figure 2 in Section 5.1 provides an ultra-scale reference topology.
Section 5.1 describes this topology. Section 5.2 presents three
design models to deploy BGP CAR in the reference topology, including
hierarchical options. Section 5.3 analyses analyzes the logical scaling
properties of each model.
Filtering techniques described in the previous section allow a PE to
limit the CAR routes that it needs to learn or install. Scaling
benefits of on-demand BGP subscription and filtering will be
described in a separate document.
5.1. Ultra-Scale Reference Topology
RD:V/v via E2
+-----+ +-----+ vpn label:30030 +-----+
....... |S-RR1| <........... |S-RR2| <...............|S-RR3| <......
: +-----+ +-----+ Color C1 +-----+ :
: :
: :
: :
+:------------+--------------+--------------+--------------+--------:-+
|: | | | | : |
|: | | | | : |
|: +---+ +---+ +---+ +---+ : |
|: |121| |231| |341| |451| : |
|: +---+ +---+ +---+ +---+ : |
|---+ | | | | +---|
| E1| | | | | | E2|
|---+ | | | | +---|
| +---+ +---+ +---+ +---+ |
| |122| |232| |342| |452| |
| +---+ +---+ +---+ +---+ |
| Access | Metro | Core | Metro | Access |
| domain 1 | domain 2 | domain 3 | domain 4 | domain 5 |
+-------------+--------------+--------------+--------------+----------+
iPE iBRM iBRC eBRC eBRM ePE
Figure 2: Ultra-Scale Reference Topology
The following description applies to the reference topology above:
* Independent IS-IS/OSPF SR instance in each domain.
* Each domain has Flex Algo 128. Prefix SID Prefix-SID for a node is SRGB Segment
Routing Global Block (SRGB) 168000 plus node number.
* A BGP CAR route (E2, C1) is advertised by egress BRM node 451.
The route is sourced locally from redistribution from IGP-FA 128.
* Not shown for simplicity, node 452 will also advertise (E2, C1).
* When a transport RR is used within the domain or across domains,
ADD-PATH is enabled to advertise paths from both egress BRs to
it's its
clients.
* Egress PE E2 advertises a VPN route RD:V/v with BGP Color extended
community Color-EC C1
that propagates via service RRs to ingress PE E1.
* E1 steers V/v prefix via color-aware path (E2, C1) and VPN label
30030.
5.2. Deployment Model
5.2.1. Flat
RD:V/v via E2
+-----+ +-----+ vpn label:30030 +-----+
....... |S-RR1| <........... |S-RR2| <...............|S-RR3| <......
: +-----+ +-----+ Color C1 +-----+ :
: :
: :
: :
+:------------+--------------+--------------+--------------+--------:-+
|: | | | | : |
|: | (E2,C1) | (E2,C1) | (E2,C1) | : |
|: +---+ via 231 +---+ via 341 +---+ via 451 +---+ : |
|:(E2,C1) |121|<---------|231|<---------|341|<---------|451| : |
|: via 121 /+---+ L=168002 +---+ L=168002 +---+ L=168002 +---+ : |
|---+ / | | | | +---|
| E1| <--/ | | | | | E2|
|---+ L=168002| | | | +---|
| +---+ +---+ +---+ +---+ |
| |122| |232| |342| |452| |
| +---+ +---+ +---+ +---+ |
| Access | Metro | Core | Metro | Access |
| domain 1 | domain 2 | domain 3 | domain 4 | domain 5 |
+-------------+--------------+--------------+--------------+----------+
iPE iBRM iBRC eBRC eBRM ePE
168121 168231 168341 168451
168002 168002 168002 168002 168002
30030 30030 30030 30030 30030 30030
Figure 3: Flat Transport Network Design
* Node 451 advertises BGP CAR route (E2, C1) to 341, from which it
goes to 231 231, then to 121 121, and finally to E1.
* Each BGP hop allocates local label and programs swap entry in
forwarding for (E2, C1).
* E1 receives BGP CAR route (E2, C1) via 121 with label 168002.
- Let's assume E1 selects that path.
* E1 resolves BGP CAR route (E2, C1) via 121 on color-aware path
(121, C1).
- Color-aware path (121, C1) is FA128 path to 121 (label 168121).
* E1's imposition color-aware label-stack label stack for V/v is thus thus:
- 30030 <=> V/v
- 168002 <=> (E2, C1)
- 168121 <=> (121, C1)
* Each BGP hop performs swap operation on 168002 bound to color-
aware path (E2, C1).
5.2.2. Hierarchical Design with Next-Hop-Self at Ingress Domain BR
(E2,C1)
+-----+ via 451 +-----+
|T-RR1| <-------------- |T-RR2|
/ +-----+ L=168002 +-----+\
/ \
+-------------+---/----------+--------------+-----------\--+----------+
| | / | | \ | |
| (E2,C1) | / (451,C1) | (451,C1) | \| |
| via 121 +---+ via 231 +---+ via 341 +---+ +---+ |
| L=168002 |121| <======= |231| <========|341| <======= |451| |
| / +---+ L=168451 +---+ L=168451 +---+ +---+ |
|---+ / | | | | +---|
| E1|<--/ | | | | | E2|
|---+ | | | | +---|
| +---+ +---+ +---+ +---+ |
| |122| |232| |342| |452| |
| +---+ +---+ +---+ +---+ |
| Access | Metro | Core | Metro | Access |
| domain 1 | domain 2 | domain 3 | domain 4 | domain 5 |
+-------------+--------------+--------------+--------------+----------+
iPE iBRM iBRC eBRC eBRM ePE
168231 168341
168121 168451 168451 168451
168002 168002 168002 168002 168002
30030 30030 30030 30030 30030 30030
Figure 4: Hierarchical BGP transport Transport CAR, Next-Hop-Self (NHS) at iBR
* Node 451 advertises BGP CAR route (451, C1) to 341, from which it
goes to 231 231, and finally to 121.
* Each BGP hop allocates local label and programs swap entry in
forwarding for (451, C1).
* 121 resolves received BGP CAR route (451, C1) via 231 (label
168451) on color-aware path (231, C1).
- Color-aware path (231, C1) is FA128 path to 231 (label 168231).
* 451 advertises BGP CAR route (E2, C1) via 451 to transport RR
T-RR2, which reflects it to transport RR T-RR1, which reflects it
to 121.
* 121 receives BGP CAR route (E2, C1) via 451 with label 168002.
- Let's assume 121 selects that path.
* 121 resolves BGP CAR route (E2, C1) via 451 on color-aware path
(451, C1).
- Color-aware path (451, C1) is BGP CAR path to 451 (label
168451).
* 121 imposition of color-aware label stack for (E2, C1) is thus thus:
- 168002 <=> (E2, C1)
- 168451 <=> (451, C1)
- 168231 <=> (231, C1)
* 121 advertises (E2, C1) to E1 with next hop self next-hop-self (121) and label
168002
168002.
* E1 constructs same imposition color-aware label-stack label stack for V/v via
(E2, C1) as in the flat model:
- 30030 <=> V/v
- 168002 <=> (E2, C1)
- 168121 <=> (121, C1)
* 121 performs swap operation on 168002 with hierarchical color-
aware label stack for (E2, C1) via 451 from step 7.
* Nodes 231 and 341 perform swap operation on 168451 bound to color-
aware path (451, C1).
* 451 performs swap operation on 168002 bound to color-aware path
(E2, C1).
Note: E1 does not need the BGP CAR route (451, C1) in this design.
5.2.3. Hierarchical Design with Next-Hop-Unchanged at Ingress Domain BR
(E2,C1)
+-----+ via 451 +-----+
|T-RR1| <-------------- |T-RR2|
/ +-----+ L=168002 +-----+\
/ \
+-------------+---/----------+--------------+-----------\--+----------+
| | / | | \ | |
| (E2,C1) | / (451,C1) | (451,C1) | \| |
| via 451 +---+ via 231 +---+ via 341 +---+ +---+ |
| L=168002/|121| <======= |231| <========|341| <======= |451| |
| / +---+ L=168451 +---+ L=168451 +---+ +---+ |
|---+ <--/ //| | | | +---|
| E1| // | | | | | E2|
|---+ <===// | | | | +---|
| (451,C1) +---+ +---+ +---+ +---+ |
| via 121 |122| |232| |342| |452| |
| L=168451 +---+ +---+ +---+ +---+ |
| | | | | |
| Access | Metro | Core | Metro | Access |
| domain 1 | domain 2 | domain 3 | domain 4 | domain 5 |
+-------------+--------------+--------------+--------------+----------+
iPE iBRM iBRC eBRC eBRM ePE
168121 168231 168341
168451 168451 168451 168451
168002 168002 168002 168002 168002
30030 30030 30030 30030 30030 30030
Figure 5: Hierarchical BGP transport Transport CAR, Next-Hop-Unchanged
(NHU) at iBR
* Nodes 341, 231 231, and 121 receive and resolve BGP CAR route (451,
C1) the same as in the previous model.
* Node 121 allocates local label and programs swap entry in
forwarding for (451, C1).
* 451 advertises BGP CAR route (E2, C1) to transport RR T-RR2, which
reflects it to transport RR T-RR1, which reflects it to 121.
* Node 121 advertises (E2, C1) to E1 with next hop as 451; i.e.,
next-hop-unchanged. 451 (i.e.,
next-hop-unchanged).
* 121 also advertises (451, C1) to E1 with next hop self next-hop-self (121) and
label 168451.
* E1 resolves BGP CAR route (451, C1) via 121 on color-aware path
(121, C1).
- Color-aware path (121, C1) is FA128 path to 121 (label 168121).
* E1 receives BGP CAR route (E2, C1) via 451 with label 168002.
- Let's assume E1 selects that path.
* E1 resolves BGP CAR route (E2, C1) via 451 on color-aware path
(451, C1).
- Color-aware path (451, C1) is BGP CAR path to 451 (label
168451).
* E1's imposition color-aware label-stack label stack for V/v is thus thus:
- 30030 <=> V/v
- 168002 <=> (E2, C1)
- 168451 <=> (451, C1)
- 168121 <=> (121, C1)
* Nodes 121, 231 231, and 341 perform swap operation on 168451 bound to
(451, C1).
* 451 performs swap operation on 168002 bound to color-aware path
(E2, C1).
5.3. Scale Analysis
The following two tables summarize the logically analyzed scaling of
the control-plane and data-plane for these the previous three models:
+=======+=====================+=====================+=============+
| | E1 | 121 | 231
-----+---------------------+---------------------+-------------------- |
+=======+=====================+=====================+=============+
| FLAT | (E2,C) via (121,C) | (E2,C) via (231,C) | (E2,C) via |
| | | | (341,C)
-----+---------------------+---------------------+--------------------
H.NHS| |
+=======+---------------------+---------------------+-------------+
| H.NHS | (E2,C) via (121,C) | (E2,C) via (451,C) | (451,C) via |
| | | (451,C) via (231,C) | (451,C) via (341,C)
-----+---------------------+---------------------+--------------------
H.NHU| |
+=======+---------------------+---------------------+-------------+
| H.NHU | (E2,C) via (451,C) | |
| (451,C) via (121,C) (231,C) | (451,C) via (231,C) |
| | (451,C) via (121,C) | | (341,C)
-----+---------------------+---------------------+-------------------- |
+=======+---------------------+---------------------+-------------+
Table 1
+=======+============+==================+==================+
| | E1 | 121 | 231
-----+---------------------+---------------------+-------------------- |
+=======+============+==================+==================+
| FLAT | V -> 30030 | 168002 -> 168002 | 168002 -> 168002 |
| | 168002 | 168231 | 168341 |
| | 168121 | |
-----+---------------------+---------------------+--------------------
H.NHS| |
+=======+------------+------------------+------------------+
| H.NHS | V -> 30030 | 168002 -> 168002 | 168451 -> 168451 |
| | 168002 | 168451 | 168341 |
| | 168121 | 168231 |
-----+---------------------+---------------------+--------------------
H.NHU| |
+=======+------------+------------------+------------------+
| H.NHU | V -> 30030 | 168451 -> 168451 | 168451 -> 168451 |
| | 168002 | 168231 | 168341 |
| | 168451 | | |
| | 168121 | |
-----+---------------------+---------------------+-------------------- |
+=======+------------+------------------+------------------+
Table 2
* The flat model is the simplest design, with a single BGP transport
level. It results in the minimum label/SID stack at each BGP hop.
However, it significantly increases the scale impact on the core
BRs (e.g. (e.g., 341), whose FIB capacity and even MPLS label space may
be exceeded.
- 341's data-plane scales with (E2, C) where there may be 300k
E's Es
and 5 C's Cs, hence 1.5M entries > 1M MPLS data-plane.
* The hierarchical models avoid the need for core BRs to learn
routes and install label forwarding entries for (E, C) routes.
- Whether next hop is set to self or left unchanged at 121, 341's
data-plane scales with (451, C) where there may be thousands of
451's
451s and 5 C's. Cs. Therefore, this scaling is well under the 1
million MPLS labels data-plane limit.
- They also aid faster convergence by allowing the PE routes to
be distributed via out-of-band RRs that can be scaled
independent of the transport BRs.
* The next-hop-self option at ingress BRM (e.g. (e.g., 121) hides the
hierarchical design from the ingress PE, keeping its outgoing
label programming as simple as the flat model. However, the
ingress BRM requires an additional BGP transport level recursion,
which coupled with load-balancing adds data-plane complexity. It
needs to support a swap and push operation. It also needs to
install label forwarding entries for the egress PEs that are of
interest to its local ingress PEs.
* With the next-hop-unchanged option at ingress BRM (e.g. (e.g., 121),
only an ingress PE needs to learn and install output label entries
for egress (E, C) routes. The ingress BRM only installs label
forwarding entries for the egress ABR (e.g. (e.g., 451). However, the
ingress PE needs an additional BGP transport level recursion and
pushes a BGP VPN label and two BGP transport labels. It may also
need to handle load-balancing for the egress ABRs. This is the
most complex data-plane option for the ingress PE.
5.4. Anycast SID
This section describes how Anycast SID complements and improves the
scaling designs above.
5.4.1. Anycast SID for Transit Inter-domain Inter-Domain Nodes
* Redundant BRs (e.g. (e.g., two egress BRMs, 451 and 452) advertise BGP
CAR routes for a local PE (e.g., E2) with the same SID (based on
label index). Such egress BRMs may be assigned a common Anycast
SID, so that the BGP next hops for these routes will also resolve
via a color-aware path to the Anycast SID.
* The use of Anycast SID naturally provides fast local convergence
upon failure of an egress BRM node. In addition, it decreases the
recursive resolution and load-balancing complexity at an ingress
BRM or PE in the hierarchical designs above.
5.4.2. Anycast SID for Transport Color Endpoints (e.g., PEs)
The common Anycast SID technique may also be used for a redundant
pair of PEs that share an identical set of service (VPN) attachments.
* For example, assume a node E2' is paired with E2 above (e.g.,
Figure 5). Both PEs should be configured with the same static
label/SID for the services (e.g., per-VRF VPN label/SID), and will
advertise associated service routes with the Anycast IP as BGP
next hop.
* This design provides a convergence and recursive resolution
benefit on an ingress PE or ABR similar to the egress ABR case in
the previous section (Section 5.4.1).
Section 5.4.1. However, its applicability is limited to cases
where the above constraints can be met.
6. Routing Convergence
BGP CAR leverages existing well-known design techniques to provide
fast convergence.
Section 2.7 describes how BGP CAR provides localized convergence
within a domain for BR failures, including originating BRs, without
propagating failure churn into other domains.
Anycast SID techniques described in Section 5.4 can provide further
convergence optimizations for BR and PE failures deployed in
redundant designs.
7. CAR SRv6
7.1. Overview
Steering services over SRv6 based SRv6-based intent-aware multi-domain transport
paths may be categorized into two distinct cases that are described
in Section 5 of [RFC9252]. Both cases are supported by BGP CAR, as
described below.
7.1.1. Routed Service SID
The SRv6 Service SID that is advertised with a service route is
allocated by an egress PE from a routed intent-aware locator prefix
(Section 3.3 of [RFC8986]). Service steering at an ingress PE is via
resolution of the Service SID signaled with the service route as
described in ([RFC9252]). [RFC9252].
The intent-aware transport path to the SRv6 locator of the egress PE
is provided by underlay IP routing. Underlay IP routing can include
IGP Flex-Algo [RFC9350] within a domain, and BGP CAR [this document] (as defined in
this document) across multiple IGP domains or BGP ASes.
An SRv6 locator prefix is assigned for a given intent or color. The
SRv6 locator may be shared with an IGP Flex-Algo, or it may be
assigned specific to BGP CAR for a given intent.
Distribution of SRv6 locators in BGP CAR SAFI:
* In a multi-domain network, the SRv6 locator prefix is distributed
using BGP CAR SAFI to ingress PEs and ASBRs in a remote domain.
The SRv6 locator prefix may be advertised in the BGP CAR SAFI from
an egress PE, or redistributed into BGP CAR from an IGP-FlexAlgo
at a BR. The locator prefix may also be summarized on a border
node along the path and a summary route distributed to ingress
PEs.
* An IP Prefix CAR route (Type-2) is defined to distribute SRv6
locator prefixes and described in Section Sections 2.9.4 and Section 8.
* A BGP CAR advertised SRv6 locator prefix may also be used for
resolution of the SRv6 service Service SID advertised for best-effort
connectivity.
Appendix
Appendices C.1 and Appendix C.2 illustrates illustrate the control control, and forwarding
behaviors for routed SRv6 Service SID. SIDs.
Section 7.2 describes the deployment options.
Section 7.3 describes operational considerations of using BGP CAR
SAFI vs versus BGP IPv6 SAFI for inter-domain route distribution of SRv6
locators.
7.1.2. Non-routed Non-Routed Service SID
The SRv6 Service SID allocated by an egress PE is not routed. The
service route carrying the non-routed SRv6 Service SID is advertised
by the egress PE with a Color-EC C ([RFC9252] section ([RFC9252], Section 5). An
ingress PE in a remote domain steers traffic for the received service
route with Color-EC C and this SRv6 Service SID as described below.
BGP CAR distribution of (E, C) underlay route:
* The intent-aware path to the egress PE within the egress domain is
provided by an SR-TE or similar policy (E, C) [RFC9256]. This (E,
C) policy is distributed into the multi-domain network from egress
BRs using a BGP CAR (E, C) route towards ingress PEs in other
domains. This signaling is the same as for SR-MPLS as described
in earlier sections.
* The (E, C) BGP CAR Type-1 route is advertised from a BR with an
SRv6 transport SID allocated from an SRv6 locator assigned for the
intent C. An SR-PCE or local configuration may ensure multiple
BRs in the egress domain that originate the (E, C) route advertise
the same SRv6 transport SID.
BGP CAR distribution of SRv6 locator underlay route:
* BGP CAR MAY also provide the underlay intent-aware inter-domain
route to resolve the intent-aware SRv6 transport SID advertised
with the (E, C) BGP CAR route as follows:
- An egress domain BR has a an SRv6 locator prefix that covers the
SRv6 transport SID allocated by the egress BR for the (E, C)
BGP CAR route.
- The egress domain BR advertises an IP Prefix Type-2 CAR route
for the SRv6 locator prefix, and the route is distributed
across BGP hops in the underlay towards ingress PEs. This
distribution is the same as the previous case in Section 7.1.1 case. 7.1.1.
The route may also be summarized in another CAR type-2 Type-2 route
prefix.
Service traffic steering and SRv6 transport SID resolution at ingress
PE:
* An ingress PE in a remote domain resolves the received service
route with Color color C via the (E, C) BGP CAR route above, as
described in Section 3.
* Additionally, the ingress PE resolves the SRv6 transport SID
received in the BGP CAR (E, C) route via the BGP CAR IP Prefix
route, similar to the SRv6 Routed Service SID resolution in
Section 7.1.1.
- Multiple (E, C) routes may resolve via a single IP Prefix CAR
route.
o Resolution of (E, C) routes over IP Prefix CAR routes is the
typical resolution order as the IP Prefix route provides
intent-aware reachability to the BRs that advertise the (E,
C) specific routes for each egress PE. However, there can
be use-cases use cases where a an IP Prefix CAR route may resolve via a
(E, C) route.
* The ingress PE via the recursive resolution above builds the
packet encapsulation that contains the SRv6 Service SID and the
received (E, C) route's SRv6 transport SID in the SID-list. SID list.
Appendix C.3 contains an example that illustrates the control plane
distribution, recursive resolution and forwarding behaviors described
above.
Note: An SR-policy may also be defined for multi-domain end to end
[RFC9256], independent of BGP CAR. In that case, both BGP CAR and
SR-TE inter-domain paths may be available at an ingress PE for an (E,
C) route (Section 1.2).
7.2. Deployment Options For for CAR SRv6 Locator Reachability Distribution
and Forwarding
Since an SRv6 locator (or summary) is an IPv6 prefix, it will be
installed into the IPv6 forwarding table on a BGP router (e.g., ABR
or ASBR), ASBR) for packet forwarding. With the use of IPv6 locator
prefixes, there is no need to allocate and install per-PE SIDs on
each BGP hop to forward packets.
A few options to forward packets for BGP SRv6 prefixes described in
([I-D.ietf-spring-srv6-mpls-interworking]
[SRv6-INTERWORK] also apply to BGP CAR. These options are described
in Section Sections 7.2.1 and Section 7.2.2.
7.2.1. Hop by Hop Hop-by-Hop IPv6 Forwarding for BGP SRv6 Prefixes
This option employs hop by hop hop-by-hop IPv6 lookup and forwarding on both BRs
and P nodes in a domain along the path of propagation of BGP CAR
routes. This option's procedures include the following:
* In addition to BRs, P nodes within a domain also learn BGP CAR IP
Prefix routes (for SRv6) and install them into the forwarding
table.
* BGP routing is enabled on all internal nodes (iBGP) using full-
mesh or an RR.
* BRs distribute external BGP SRv6 routes to internal peers
including P routers, with the following conditions:
- The the external BGP Next-hop next hop is advertised unchanged to the
internal peers;
- Internal internal nodes use recursive resolution via IGP at each hop to
forward IPv6 packets towards the external BGP next-hop; next hop; and
- Resolution resolution is per intent/color (e.g., via IGP IPv6 FlexAlgo).
This design is illustrated with an example in Appendix C.1.
The benefits of this scheme are:
* Simpler A simpler design, as no tunnel encapsulation is required between
BRs in a domain.
* No per-PE SID allocation and installation on any BGP hop.
* This design is similar to the well-known Internet / BGP hop-by-hop
IP routing model and can support large scale large-scale route distribution.
* In addition, since SRv6 locator prefixes can be summarized, this
minimizes the number of routes routes, and hence the scale requirements
on P routers.
7.2.2. Encapsulation between Between BRs for BGP SRv6 Prefixes
In this design, IPv6 lookup and forwarding for BGP SRv6 prefixes are
only done on BGP BRs. This option includes the following procedures:
* These nodes use SRv6 (or other) encapsulation encapsulations to reach the BGP
SRv6 next hop.
- SRv6 outer encapsulation may be H.Encaps.Red.
- Encapsulation is not needed for directly connected next hops,
such as with eBGP single-hop sessions.
* BGP route distribution is enabled between BRs via RRs, or directly
if single-hop BGP.
* An egress BR sets itself as BGP next hop, and selects and
advertises an appropriate encapsulation towards itself.
- If SRv6 encapsulation, then the SRv6 SID advertised from egress
BR is from an SRv6 locator for the specific intent within the
domain. Multiple BGP SRv6 prefixes may share a common SID,
avoiding per-PE SID allocation and installation on any BGP hop.
- If MPLS/SR-MPLS transport, the route will carry label/prefix-
SID the label/
Prefix-SID allocated by the next hop, may be shared.
* An ingress BR encapsulates SRv6 egress PE destined packets with
encapsulation to BGP next hop, ie. hop (i.e., the egress BR.
Benefits BR).
The benefits of this scheme are:
* P nodes do not need to learn or install BGP SRv6 prefixes in this
(BGP-free core) design.
* No per-PE SID allocation and installation on any BGP hop.
This design is illustrated in Appendix C.2.
7.3. Operational Benefits of using Using CAR SAFI for SRv6 Locator Prefix
Distribution
When reachability to an SRv6 SID is provided by distribution of a
locator prefix via underlay routing, BGP IPv6 SAFI (AFI/SAFI=2/1) may
also be used for inter-domain distribution of these IPv6 prefixes as
described in [I-D.ietf-spring-srv6-mpls-interworking] (Section 7.1.2) Section 7.1.2 of [SRv6-INTERWORK] or [I-D.ietf-idr-cpr]. [RFC9723].
Using the BGP CAR SAFI provides the following operational benefits:
* CAR SAFI is a separate BGP SAFI used for underlay transport
intent-aware routing. It avoids overloading of BGP IPv6 SAFI,
which also carries Internet (service) prefixes. Using CAR SAFI
provides:
- Automatic separation of SRv6 locator (transport) routes from
Internet (service) routes,
o Preventing preventing inadvertent leaking of routes. routes, and
o Avoiding avoiding the need to configure specific route filters for
locator routes.
- Priority handling of infrastructure routes over service
(Internet) routes.
* CAR SAFI also supports inter-domain distribution of (E, C) routes
sourced from SR-Policy, in addition to SRv6 locator IPv6 prefixes.
* CAR SAFI may also be used for best-effort routes in addition to
intent-aware routes as described in the next section.
Note: If infrastructure routes such as SRv6 locator routes are
carried in both BGP-IP [RFC4271] / BGP-LU [RFC8277, RFC4798], [RFC8277] [RFC4798], and
BGP CAR, Section 8 describes the path selection preference between
them.
8. CAR IP Prefix Route
An IP Prefix CAR route is a route type (Type-2) that carries a
routable IP prefix whose processing follows the semantics of
[RFC4271] and [RFC2545]
semantics. [RFC2545]. IP Prefix CAR routes are installed in the
default routing and forwarding table and provide longest-prefix-match
forwarding. This is unlike Type-1 (E, C) routes, where it is the
signaled forwarding data such as labels/SIDs that are installed in
the forwarding table to create end to end end-to-end paths.
IP Prefix CAR routes may be originated into BGP CAR SAFI either from
an egress PE or from a BR in a domain. Type-2 routes carry
infrastructure routes for both IPv4 and IPv6.
As described in Section 2.1, it is used for cases where a unique
routable IP prefix is assigned for a given intent or color. It may
also be used for routes providing best-effort connectivity.
A few applicable example use-cases: use cases:
* SRv6 locator prefix with color for specific intents.
* SRv6 locator prefix without color for best-effort.
* Best effort Best-effort transport reachability to a PE/BR without color.
For specific intents, color may be signaled with the IP Prefix CAR
route for purposes such as intent-aware SRv6 SID or BGP next-hop next hop
selection at each transit BR, color based color-based routing policies and
filtering, and intent-aware next-hop resolution (Section 2.5). These
purposes are the same as with (E, C) routes. For such purposes,
color associated with the CAR IP Prefix route is signaled using LCM-
EC.
Reminder: LCM-EC conveys end-to-end intent/color associated with
route/NLRI. When traversing network domain(s) where a different
intent/color is used for next-hop resolution, BGP Color-EC may
additionally be used as in Section 2.10.
A special case of intent is best-effort best-effort, which may be represented by
a color and follow the above procedures. But However, to be compatible
with traditional operational usage, the CAR IP Prefix route is
allowed to be without color for best-effort. In this case, the
routes will not carry an LCM-EC. Resolution is described in
Section 2.5.
As described in Section 7.3, infrastructure prefixes are intended to
be carried in CAR SAFI instead of SAFIs that also carry service
routes such as BGP-IP (SAFI 1, [RFC4271]) and BGP-LU (SAFI 4,
[RFC4798]). However, if such infrastructure routes are also
distributed in these SAFIs, a router may receive both BGP CAR SAFI
paths and IP/LU SAFI paths. By default, the CAR SAFI transport path
is preferred over the BGP IP or BGP-LU SAFI path.
A BGP transport CAR speaker that supports packet forwarding lookup
based on the IPv6 prefix route (such as a BR) will set itself as next
hop while advertising the route to peers. It will also install the
IPv6 route into forwarding with the received next hop and/or
encapsulation. If such a transit router does not support this route
type, it will not install this route and will not set itself as next
hop, hence
hop; hence, it will not propagate the route any further.
9. VPN CAR
This section illustrates the extension of BGP CAR to address the VPN
intent-aware routing requirement stated in Section 6.1.2 of
[I-D.hr-spring-intentaware-routing-using-color].
[INTENT-AWARE]. The examples use MPLS, but other transport types can
also be used (e.g., SRv6).
CE1 -------------- PE1 -------------------- PE2 -------------- CE2 - V
* BGP CAR SAFI is enabled on CE1-PE1 and PE2-CE2 sessions sessions.
* BGP VPN CAR SAFI is enabled between PE1 and PE2 PE2.
* Provider publishes to customer that intent 'low-delay' is mapped
to color CP on its inbound peering links links.
* Within its infrastructure, Provider provider maps intent 'low-delay' to
color CPT CPT.
* On CE1 and CE2, intent 'low-delay' is mapped to CC CC.
(V, CC) is a Color-Aware color-aware route originated by CE2 CE2.
1. CE2 sends to PE2 : PE2: [(V, CC), Label L1] via CE2 with LCM-EC (CP) as
per peering agreement agreement.
2. PE2 installs in VRF A: [(V, CC), L1] via CE2 CE2, which resolves on
(CE2, CP) or connected OIF
3 Outgoing Interface (OIF).
3. PE2 allocates VPN Label L2 and programs swap entry for (V, CC) CC).
4. PE2 sends to PE1 : PE1: [(RD, V, CC), L2] via PE2, LCM-EC(CP) LCM-EC (CP) with
regular Color-EC (CPT) (CPT).
5. PE1 installs in VRF A: [(V, CC), L2] via (PE2, CPT) steered on
(PE2, CPT) CPT).
6. PE1 allocates Label L3 and programs swap entry for (V, CC) CC).
7. PE1 sends to CE1 : CE1: [(V, CC), L3] via PE1 after removing LCM-EC
through route-policy route policy.
8. CE1 installs : installs: [(V, CC), L3] via PE1 PE1, which resolves on (PE1, CC)
or connected OIF OIF.
9. Label L3 is installed as the imposition label for (V, CC) CC).
VPN CAR distribution for (RD, V, CC) requires a new SAFI that follows
the same VPN semantics as defined in [RFC4364] and also supports the
distribution of routes with the CAR NLRI and associated non-key TLVs
defined in Section 2.9 of this document.
Procedures defined in [RFC4364] and [RFC4659] apply to VPN CAR SAFI.
Further, all CAR SAFI procedures described in Section 2 above apply
to CAR SAFI enabled within a VRF. Since CE and PE are typically in
different administrative domains, LCM-EC is attached to CAR routes.
VPN CAR SAFI routes follow color based color-based steering techniques as
described in Section 3 and illustrated in the example above.
VPN CAR SAFI routes may also be advertised with a specific BGP next
hop per color, with a TEA or Tunnel Encapsulation EC EC, and follow the
procedures of [RFC9012] Section 6. 6 of [RFC9012].
CAR routes distributed in VPN CAR SAFI are infrastructure routes
advertised by CEs in different customer VRFs on a PE. Example use- use
cases are intent-aware L3VPN CsC ([RFC4364] Section 9) Carriers' Carriers (Section 9 of
[RFC4364]) and SRv6 over a provider network . network. The VPN RD
distinguishes CAR routes of different customers being advertised by
the PE.
9.1. Format and Encoding
BGP VPN CAR SAFI leverages BGP multi-protocol extensions [RFC4760]
and uses the MP_REACH_NLRI and MP_UNREACH_NLRI attributes for route
updates within SAFI value 84 along with AFI 1 for IPv4 VPN CAR
prefixes and AFI 2 for IPv6 VPN CAR prefixes.
BGP speakers MUST use the BGP Capabilities Advertisement to ensure
support for processing of BGP VPN CAR updates. This is done as
specified in [RFC4760], by using capability code 1 (multi-protocol
BGP), with AFI 1 and 2 (as required) and SAFI 84.
The Next Hop network address field in the MP_REACH_NLRI may contain
either a VPN-IPv4 or a VPN-IPv6 address with 8-octet RD set to zero,
independent of AFI. If the next hop length is 12, then the next hop
is a VPN-IPv4 address with an RD of 0 constructed as per [RFC4364].
If the next hop length is 24 or 48, then the next hop is a VPN-IPv6
address constructed as per section Section 3.2.1.1 of [RFC4659].
9.1.1. VPN CAR (E, C) NLRI Type
VPN CAR Type-1 (E, C) NLRI with RD has the format shown below below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NLRI Length | Key Length | NLRI Type |Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Distinguisher |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Distinguisher |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Prefix (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Followed
It is followed by optional Non-Key TLVs encoded as per Section 2.9.2 2.9.2.
where:
All
all fields are encoded as per Section 2.9.3 with the following
changes:
*
Key Length: This length indicates the total length comprised of the
RD, Prefix Length field, IP Prefix field, and the Color field.
*
Route Distinguisher: An 8-octet field encoded according to
[RFC4364].
*
Type-Specific Non-Key TLVs: The Label TLV, Label Index TLV TLV, and SRv6
SID TLV (Section 2.9.2) may be associated with the VPN CAR (E, C)
NLRI type.
9.1.2. VPN CAR IP Prefix NLRI Type
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NLRI Length | Key Length | NLRI Type |Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Distinguisher |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Distinguisher |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Prefix (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Followed
It is followed by optional Non-Key TLVs encoded as per Section 2.9.2 2.9.2.
where:
All
all fields are encoded as per Section 2.9.4 with the following
changes:
*
Key Length: This length indicates the total length comprised of the
RD, Prefix Length field field, and IP Prefix field.
*
Route Distinguisher: 8 octet An 8-octet field encoded according to
[RFC4364].
*
Type-Specific Non-Key TLVs: The Label TLV, Label Index TLV TLV, and SRv6
SID TLV (Section 2.9.2) may be associated with the VPN CAR IP
Prefix NLRI type.
Error
The error handling specified in Section 2.11 also applies to VPN CAR
SAFI.
10. IANA Considerations
10.1. BGP CAR SAFIs
IANA has assigned SAFI value 83 (BGP CAR) and SAFI value 84 (BGP VPN
CAR) from the "SAFI Values" sub-registry under registry in the "Subsequent Address
Family Identifiers (SAFI) Parameters" registry group with this
document as a reference.
10.2. BGP "BGP CAR NLRI Types Types" Registry
IANA is requested to create has created a "BGP CAR NLRI Types" registry in the "Border
Gateway Protocol (BGP) Parameters" registry group with this document
as a reference. The registry is for assignment of the one
octet sized code-points 1-octet code
points for BGP CAR NLRI types and is populated with the values shown
below:
+=======+========================+===========+
| Type | NLRI Type | Reference
----------------------------------------------------------------- |
+=======+========================+===========+
| 0 | Reserved [This document] | RFC 9871 |
+-------+------------------------+-----------+
| 1 | Color-Aware Route NLRI [This document] | RFC 9871 |
+-------+------------------------+-----------+
| 2 | IP Prefix NLRI [This document] | RFC 9871 |
+-------+------------------------+-----------+
| 3-255 | Unassigned |
+-------+------------------------------------+
Table 3
Allocations within the registry are to be made under with the
"Specification Required" policy as specified in [RFC8126]) [RFC8126] and in
Section 10.4.
10.3. BGP "BGP CAR NLRI TLV TLV" Registry
IANA is requested to create has created a "BGP CAR NLRI TLV Types" registry in the "Border
Gateway Protocol (BGP) Parameters" registry group with this document
as a reference. The registry is for assignment of the
6-bits sized code-points 6-bit code
points for BGP CAR NLRI non-key TLV types and is populated with the
values shown below:
+======+=================+===========+
| Type | NLRI TLV Type | Reference
----------------------------------------------------------------- |
+======+=================+===========+
| 0 | Reserved [This document] | RFC 9871 |
+------+-----------------+-----------+
| 1 | Label TLV [This document] | RFC 9871 |
+------+-----------------+-----------+
| 2 | Label Index TLV [This document] | RFC 9871 |
+------+-----------------+-----------+
| 3 | SRv6 SID TLV [This document] | RFC 9871 |
+------+-----------------+-----------+
| 4-64 | Unassigned |
+------+-----------------------------+
Table 4
Allocations within the registry are to be made under with the
"Specification Required" policy as specified in [RFC8126]) [RFC8126] and in
Section 10.4.
For a new TLV to be used with existing NLRI Types, documentation of
the NLRI Types must be updated.
10.4. Guidance for Designated Experts
In all cases of review by the Designated Expert (DE) described here,
the DE is expected to ascertain the existence of suitable
documentation (a specification) as described in [RFC8126] for BGP the
"BGP CAR NLRI Types Registry Types" registry and BGP the "BGP CAR NLRI TLV Registry. TLV" registry.
The DE is also expected to check the clarity of purpose and use of
the requested code points. Additionally, the DE must verify that any
request for one of these code points has been made available for
review and comment within the IETF: the DE will post the request to
the IDR Working Group mailing list (or a successor mailing list
designated by the IESG). The DE must ensure that any request for a
code point does not conflict with work that is active or already
published within the IETF.
The DE is expected to confirm that the specification satisfies the
requirements for Specification Required (RFC 8126 Section 4.6). the "Specification Required" policy (Section 4.6 of
[RFC8126]). In particular, as a reminder, the specification is
required to be "permanent and readily available". The DE may assume
that any document in the Internet Draft Internet-Draft or RFC repository satisfies
the requirement for permanence and availability. In other cases, and
in particular for any document not hosted by another standards
development organization, the burden of proof of permanence falls on
the applicant.
10.4.1. Additional evaluation criteria Evaluation Criteria for the BGP "BGP CAR NLRI Types Types"
Registry
* Check the interoperability between the new NLRI type and current
NLRI types specified in this document for BGP CAR SAFIs (BGP CAR
SAFI and VPN CAR SAFI), and any updates to this document.
* Check if the specification indicates which non-key TLVs are
applicable for the new NLRI Type.
10.4.2. Additional evaluation criteria Evaluation Criteria for the BGP "BGP CAR NLRI TLV TLV"
Registry
* Check the applicability of the new TLV for the BGP CAR NLRI Types
defined.
* Check the T bit setting for the new TLV TLV.
10.5. BGP Extended-Community "Border Gateway Protocol (BGP) Extended Communities" Registry
IANA has assigned the sub-type 0x1b for "Local Color Mapping (LCM)"
in the "Transitive Opaque Extended Community Sub-Types" registry
located in
the "Border Gateway Protocol (BGP) Extended Communities" registry
group.
11. Manageability and Operational Considerations
Color assignments in a multi-domain network operating under a common
or cooperating administrative control (i.e., a color domain) should
be managed similar to transport layer IP addresses, and ensure a
unique and non-conflicting color allocation across the different
network domains in that color domain. This is a logical best
practice in a single color or administrative domain, which is the
most typical deployment scenario.
When color-aware routes propagate across a color domain boundary,
there is typically no need for color assignments to be identical in
both color domains, since the IP prefix is unique in the inter-domain
transport network. This unique IP prefix provides a unique and non-
conflicting scope for the color in an (E, C) route. Co-ordination Coordination
between the operators of the color domains is needed only to enable
the color to be re-mapped into a local color (carried in the LCM-EC)
assigned for the same intent in the receiving color domain.
However, if networks under different administrative control establish
a shared transport service between them, where the same transport
service IP address is co-ordinated coordinated and shared among two (or more)
color domains domain networks, then the color assignments associated with
that shared IP address should also be co-ordinated coordinated to avoid any
conflicts in either network (Appendix A.7).
It should be noted that the color assignments coordination are is only
necessary for routes specific to the shared service IP. Colors used
for intra-domain or for inter-domain intents associated with unique
IP addresses do not need any coordination.
Extended communities (LCM-EC/Color-EC) carried in BGP CAR and Service service
routes MUST NOT be filtered, otherwise the desired intent will not be
achieved.
12. Security Considerations
This document does not change the underlying security considerations
and issues inherent in the existing BGP protocol, such as those
described in [RFC4271] and [RFC4272].
This document defines a new BGP SAFI and related extensions to carry
color aware
color-aware routes and their associated attributes. The separate
SAFI is expected to be explicitly configured by an operator. It is
also expected that the necessary BGP route policy filtering is
configured on this new SAFI to filter routing information distributed
by the routers participating in this network, at appropriate points
within and at the boundaries of this network.
Also, given that this SAFI and these mechanisms can only be enabled
through configuration of routers within an operator's network,
standard security measures should be taken to restrict access to the
management interface(s) of routers that implement these mechanisms.
Additionally, BGP sessions SHOULD be protected using the TCP
Authentication Option [RFC5925] and the Generalized TTL Security
Mechanism [RFC5082]. BGP Origin Validation origin validation [RFC6811] and BGPsec
[RFC8205] could also be used with this SAFI.
Since CAR SAFI is a separate BGP SAFI that carries transport or
infrastructure routes for routers in the operator network, it
provides automatic separation of infrastructure routes and the
service routes that are carried in existing BGP SAFIs such as BGP
IPv4/IPv6 (SAFI=1), and BGP-LU (SAFI=4) (e.g., 6PE [RFC4798]). Using
CAR SAFI thus provides better security (such as protection against
route leaking) than would be obtained by distributing the
infrastructure routes in existing SAFIs that also carry service
routes.
BGP CAR distributes label binding similar to [RFC8277] and hence [RFC8277]; hence, its
security considerations apply.
In SR deployments, BGP CAR distributes infrastructure prefixes along
with their SID information for both SR-MPLS and SRv6. These
deployments are within an SR Domain domain [RFC8402] and the security
considerations of [RFC8402] apply. Additionally, security
considerations related to SRv6 deployments that are discussed in
section
Section 9.3 of [RFC9252] also apply.
As [RFC4272] discusses, BGP is vulnerable to traffic-diversion
attacks. This SAFI routes route adds a new means by which an attacker could
cause the traffic to be diverted from its normal path. Potential
consequences include "hijacking" of traffic (insertion of an
undesired node in the path, which allows for inspection or
modification of traffic, or avoidance of security controls) or denial
of service (directing traffic to a node that doesn't desire to
receive it).
The restriction of the applicability of this SAFI to its intended
well-defined scope and the use of techniques described above limit
the likelihood of traffic diversions.
13. Contributors
13.1. Co-authors
The following people gave substantial contributions to the content of
this document and should be considered as coauthors:
Clarence Filsfils
Cisco Systems
Belgium
Email: cfilsfil@cisco.com
Bruno Decraene
Orange
France
Email: bruno.decraene@orange.com
Luay Jalil
Verizon
USA
Email: luay.jalil@verizon.com
Yuanchao Su
Alibaba, Inc
Email: yitai.syc@alibaba-inc.com
Jim Uttaro
Individual
USA
Email: juttaro@ieee.org
Jim Guichard
Futurewei
USA
Email: james.n.guichard@futurewei.com
Ketan Talaulikar
Cisco Systems
India
Email: ketant.ietf@gmail.com
Keyur Patel
Arrcus, Inc
USA
Email: keyur@arrcus.com
Haibo Wang
Huawei Technologies
China
Email: rainsword.wang@huawei.com
Jie Dong
Huawei Technologies
China
Email: jie.dong@huawei.com
13.2. Additional Contributors
Dirk Steinberg
Lapishills Consulting Limited
Germany
Email: dirk@lapishills.com
Israel Means
AT&T
USA
Email: im8327@att.com
Reza Rokui
Ciena
USA
Email: rrokui@ciena.com
14. Acknowledgements
The authors would like to acknowledge the invaluable contributions of
many collaborators towards the BGP CAR solution and this document in
providing input about use-cases, participating in brainstorming and
mailing list discussions and in reviews of the solution and draft
revisions. In addition to the contributors listed in Section 13, the
authors would like to thank Robert Raszuk, Bin Wen, Chaitanya
Yadlapalli, Satoru Matsushima, Moses Nagarajah, Gyan Mishra, Jorge
Rabadan, Daniel Voyer, Stephane Litkowski, Hannes Gredler, Jose
Liste, Jakub Horn, Brent Foster, Dave Smith, Jiri Chaloupka, Miya
Kohno, Kamran Raza, Zafar Ali, Xing Jiang, Oleksander Nestorov, Peter
Psenak, Kaliraj Vairavakkalai, Natrajan Venkataraman, Srihari Sangli,
Ran Chen and Jingrong Xie.
The authors also appreciate the detailed reviews and astute
suggestions provided by Sue Hares (as document shepherd), Jeff Haas,
Yingzhen Qu and John Scudder that have greatly improved the document.
15. References
15.1.
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2545] Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol
Extensions for IPv6 Inter-Domain Routing", RFC 2545,
DOI 10.17487/RFC2545, March 1999,
<https://www.rfc-editor.org/info/rfc2545>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <https://www.rfc-editor.org/info/rfc4360>.
[RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
R., Patel, K., and J. Guichard, "Constrained Route
Distribution for Border Gateway Protocol/MultiProtocol
Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
Private Networks (VPNs)", RFC 4684, DOI 10.17487/RFC4684,
November 2006, <https://www.rfc-editor.org/info/rfc4684>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.
[RFC7311] Mohapatra, P., Fernando, R., Rosen, E., and J. Uttaro,
"The Accumulated IGP Metric Attribute for BGP", RFC 7311,
DOI 10.17487/RFC7311, August 2014,
<https://www.rfc-editor.org/info/rfc7311>.
[RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
Patel, "Revised Error Handling for BGP UPDATE Messages",
RFC 7606, DOI 10.17487/RFC7606, August 2015,
<https://www.rfc-editor.org/info/rfc7606>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8277] Rosen, E., "Using BGP to Bind MPLS Labels to Address
Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017,
<https://www.rfc-editor.org/info/rfc8277>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8669] Previdi, S., Filsfils, C., Lindem, A., Ed., Sreekantiah,
A., and H. Gredler, "Segment Routing Prefix Segment
Identifier Extensions for BGP", RFC 8669,
DOI 10.17487/RFC8669, December 2019,
<https://www.rfc-editor.org/info/rfc8669>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
[RFC9012] Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
"The BGP Tunnel Encapsulation Attribute", RFC 9012,
DOI 10.17487/RFC9012, April 2021,
<https://www.rfc-editor.org/info/rfc9012>.
[RFC9252] Dawra, G., Ed., Talaulikar, K., Ed., Raszuk, R., Decraene,
B., Zhuang, S., and J. Rabadan, "BGP Overlay Services
Based on Segment Routing over IPv6 (SRv6)", RFC 9252,
DOI 10.17487/RFC9252, July 2022,
<https://www.rfc-editor.org/info/rfc9252>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.
[RFC9350] Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K.,
and A. Gulko, "IGP Flexible Algorithm", RFC 9350,
DOI 10.17487/RFC9350, February 2023,
<https://www.rfc-editor.org/info/rfc9350>.
15.2.
13.2. Informative References
[I-D.hr-spring-intentaware-routing-using-color]
[INTENT-AWARE]
Hegde, S., Rao, D., Uttaro, J., Bogdanov, A., and L.
Jalil, "Problem statement for Inter-domain Intent-aware
Routing using Color", Work in Progress, Internet-Draft,
draft-hr-spring-intentaware-routing-using-color-04, 31
January 2025, <https://datatracker.ietf.org/doc/html/
draft-hr-spring-intentaware-routing-using-color-04>.
[I-D.ietf-idr-cpr]
Wang, H., Dong, J., Talaulikar, K., hantao, and R. Chen,
"BGP Colored Prefix Routing (CPR) for SRv6 based
Services", Work in Progress, Internet-Draft, draft-ietf-
idr-cpr-07, 7 February 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-cpr-
07>.
[I-D.ietf-spring-srv6-mpls-interworking]
Agrawal, S., Filsfils, C., Voyer, D., Dawra, G., Li, Z.,
and S. Hegde, "SRv6 and MPLS interworking", Work in
Progress, Internet-Draft, draft-ietf-spring-srv6-mpls-
interworking-00, 17 October 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
srv6-mpls-interworking-00>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006,
<https://www.rfc-editor.org/info/rfc4272>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC4659] De Clercq, J., Ooms, D., Carugi, M., and F. Le Faucheur,
"BGP-MPLS IP Virtual Private Network (VPN) Extension for
IPv6 VPN", RFC 4659, DOI 10.17487/RFC4659, September 2006,
<https://www.rfc-editor.org/info/rfc4659>.
[RFC4798] De Clercq, J., Ooms, D., Prevost, S., and F. Le Faucheur,
"Connecting IPv6 Islands over IPv4 MPLS Using IPv6
Provider Edge Routers (6PE)", RFC 4798,
DOI 10.17487/RFC4798, February 2007,
<https://www.rfc-editor.org/info/rfc4798>.
[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
Pignataro, "The Generalized TTL Security Mechanism
(GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,
<https://www.rfc-editor.org/info/rfc5082>.
[RFC5462] Andersson, L. and R. Asati, "Multiprotocol Label Switching
(MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
Class" Field", RFC 5462, DOI 10.17487/RFC5462, February
2009, <https://www.rfc-editor.org/info/rfc5462>.
[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP
Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
June 2010, <https://www.rfc-editor.org/info/rfc5925>.
[RFC6811] Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R.
Austein, "BGP Prefix Origin Validation", RFC 6811,
DOI 10.17487/RFC6811, January 2013,
<https://www.rfc-editor.org/info/rfc6811>.
[RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder,
"Advertisement of Multiple Paths in BGP", RFC 7911,
DOI 10.17487/RFC7911, July 2016,
<https://www.rfc-editor.org/info/rfc7911>.
[RFC8205] Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol
Specification", RFC 8205, DOI 10.17487/RFC8205, September
2017, <https://www.rfc-editor.org/info/rfc8205>.
[RFC9315] Clemm, A., Ciavaglia, L., Granville, L. Z., and J.
Tantsura, "Intent-Based Networking - Concepts and
Definitions", RFC 9315, DOI 10.17487/RFC9315, October
2022, <https://www.rfc-editor.org/info/rfc9315>.
[RFC9723] Wang, H., Dong, J., Talaulikar, K., Han, T., and R. Chen,
"BGP Colored Prefix Routing (CPR) for Services Based on
Segment Routing over IPv6 (SRv6)", RFC 9723,
DOI 10.17487/RFC9723, May 2025,
<https://www.rfc-editor.org/info/rfc9723>.
[SRv6-INTERWORK]
Agrawal, S., Filsfils, C., Voyer, D., Dawra, G., Li, Z.,
and S. Hegde, "SRv6 and MPLS interworking", Work in
Progress, Internet-Draft, draft-ietf-spring-srv6-mpls-
interworking-01, 7 July 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
srv6-mpls-interworking-01>.
Appendix A. Illustrations of Service Steering
The following sub-sections illustrate example scenarios of Colored
Service Route Steering colored
service route steering over E2E end-to-end (E2E) BGP CAR paths, resolving
over different intra-domain mechanisms.
The examples in this section use MPLS/SR for the transport data
plane. Scenarios related to SRv6 encapsulation are in a section
below.
A.1. E2E BGP transport Transport CAR intent realized using Intent Realized Using IGP Flex-Algo
RD:V/v via E2
+-----+ vpn label: 30030 +-----+
...... |S-RR1| <..................................|S-RR2| <.......
: +-----+ Color C1 +-----+ :
: :
: :
: :
+-:-----------------------+----------------------+------------------:--+
| : | | : |
| : | | : |
| : (E2,C1) via 121 | (E2,C1) via 231 | (E2,C1)via E2 : |
| : L=168002,AIGP=110 +---+ L=168002,AIGP=10 +---+ L=0x3,LI=8002 : |
| : |-------------------|121|<-----------------|231|<-------------| : |
| : V LI=8002 +---+ LI=8002 +---+ | : |
|----+ | | +-----|
| E1 | | | | E2 |
|----+(E2,C1) via 122 | (E2,C1) via 232 | (E2,C1)via E2+-----|
| ^ L=168002,AIGP=210 +---+ L=168002,AIGP=20 +---+ L=0x3 | |
| |---------------- |122|<-----------------|232|<-------------| |
| LI=8002 +---+ LI=8002 +---+ LI=8002 |
| | | |
| IS-IS SR | IS-IS SR | IS-IS SR |
| FA 128 | FA 128 | FA 128 |
+-------------------------+----------------------+---------------------+
iPE iABR eABR ePE
---------direction of traffic-------->
+------+ +------+
|168121| |168231|
+------+ +------+
+------+ +------+ +------+
|168002| |168002| |168002|
+------+ +------+ +------+
+------+ +------+ +------+
|30030 | |30030 | |30030 |
+------+ +------+ +------+
Figure 6: BGP FA Aware transport Transport CAR path Path
Use case: Provide end to end end-to-end intent for service flows.
* The following description applies to the reference topology above:
- IGP FA 128 is running in each domain, and mapped to Color color C1.
- Egress PE E2 advertises a VPN route RD:V/v colored with Color-
EC C1 to steer traffic to BGP transport CAR (E2, C1). VPN
route propagates via service RRs to ingress PE E1.
- BGP CAR route (E2, C1) with next hop, label index index, and label as
shown above are advertised through border routers in each
domain. When a an RR is used in the domain, ADD-PATH is enabled
to advertise multiple available paths.
- On each BGP hop, the (E2, C1) route's next hop is resolved over
IGP FA 128 of the domain. The AIGP attribute influences the
BGP CAR route best path decision as per [RFC7311]. The BGP CAR
label swap entry is installed that goes over FA 128 LSP to next
hop providing intent in each IGP domain. The AIGP metric
should be updated to reflect FA 128 metric to next hop.
- Ingress PE E1 learns CAR route (E2, C1). It steers colored VPN
route RD:V/v into (E2, C1).
* Important:
- IGP FA 128 top label provides intent within each domain.
- BGP CAR label (e.g. (e.g., 168002) carries end to end end-to-end intent. Thus Thus,
it stitches intent over intra-domain FA 128.
A.2. E2E BGP transport Transport CAR intent realized using Intent Realized Using SR Policy
RD:1/8 via E2
+-----+ vpn label: 30030 +-----+
...... |S-RR1| <..................................|S-RR2| <......
: +-----+ Color C1 +-----+ :
: :
: :
: :
+-:-----------------------+----------------------+------------------:-+
| : | | : |
| : | | : |
| : <-(E2,C1) via 121 | <-(E2,C1) via 231 | <-(E2,C1)via E2 : |
| : +---+ +---+ : |
| : ------------------>|121|----------------->|231|--------------| : |
| : | SR policy(C1,121) +---+ SR policy(C1,231)+---+ SR policy v : |
|----+ | | (C1,E2) +---|
| E1 | | | |E2 |
|----+ <-(E2,C1) via 122 | (E2,C1) via 232 | <-(E2,C1)via E2+---|
| | +---+ +---+ ^ |
| ------------------>|122|----------------->|232|---------------| |
| SR policy(C1,122) +---+ SR policy(C1,232)+---+ SR policy(C1,E2) |
| | | |
| | | |
| IS-IS SR | IS-IS SR | IS-IS SR |
+-------------------------+----------------------+--------------------+
iPE iABR eABR ePE
---------direction of traffic-------->
+------+ +------+
| S1 | | S2 |
+------+ +------+
+------+ +------+ +------+
|160121| |160231| | S3 |
+------+ +------+ +------+
+------+ +------+ +------+
|168002| |168002| |168002|
+------+ +------+ +------+
+------+ +------+ +------+
|30030 | |30030 | |30030 |
+------+ +------+ +------+
Figure 7: BGP SR policy Policy Aware transport Transport CAR path Path
Use case: Provide end to end end-to-end intent for service flows.
* The following description applies to the reference topology above:
- An SR Policy provides intra-domain intent. The following are
the example SID lists that are realized from SR policies in
each domain and correspond to the label stack shown in
Figure 7 7:
o SR policy (C1,121) (C1, 121) segments <S1, 121>,
o SR policy (C1,231) (C1, 231) segments <S2, 231>, and
o SR policy (C1,E2) (C1, E2) segments <S3, E2>.
- Egress PE E2 advertises a VPN route RD:V/v colored with Color-
EC C1 to steer traffic to BGP transport CAR (E2, C1). VPN
route propagates via service RRs to ingress PE E1.
- BGP CAR route (E2, C1) with next hop, label index index, and label as
shown above are advertised through border routers in each
domain. When a an RR is used in the domain, ADD-PATH is enabled
to advertise multiple available paths.
- On each BGP hop, the CAR route (E2, C1) next hop is resolved
over an SR policy (C1, next hop). The BGP CAR label swap entry
is installed that goes over SR policy segment list.
- Ingress PE E1 learns CAR route (E2, C1). It steers colored VPN
route RD:V/v into (E2, C1).
* Important:
- SR policy provides intent within each domain.
- BGP CAR label (e.g. (e.g., 168002) carries end to end end-to-end intent. Thus Thus,
it stitches intent over intra-domain SR policies.
A.3. BGP transport Transport CAR intent realized Intent Realized in a section Section of the network Network
A.3.1. Provide intent Intent for service flows only Service Flows Only in core domain running Core Domain Running IS-
IS Flex-Algo
RD:1/8 via E2
+-----+ vpn label: 30030 +-----+
...... |S-RR1| <..................................|S-RR2| <.......
: +-----+ Color C1 +-----+ :
: :
: :
: :
+-:-----------------------+----------------------+------------------:--+
| : | | : |
| : | | : |
| : (E2,C1) via 121 | (E2,C1) via 231 | (E2,C1) via E2 : |
| : L=168002,AIGP=1110+---+L=168002,AIGP=1010+---+ L=0x3 : |
| : |-------------------|121|<-----------------|231|<-------------| : |
| : V LI=8002 +---+ LI=8002 +---+ | : |
|----+ | | +-----|
| E1 | | | | E2 |
|----+(E2,C1) via 122 | (E2,C1) via 232 | (E2,C1) via E2+-----|
| ^ L=168002,AIGP=1210+---+L=168002,AIGP=1020+---+ L=0x3 | |
| |---------------- |122|<-----------------|232|<-------------| |
| LI=8002 +---+ LI=8002 +---+ |
| | | |
| IS-IS SR | IS-IS SR | IS-IS SR |
| Algo 0 | Flex-Algo 128 | Algo 0 |
| Access | Core | Access |
+-------------------------+----------------------+---------------------+
iPE iABR eABR ePE
---------direction of traffic-------->
+------+ +------+
|160121| |168231|
+------+ +------+
+------+ +------+ +------+
|168002| |168002| |160002|
+------+ +------+ +------+
+------+ +------+ +------+
|30030 | |30030 | |30030 |
+------+ +------+ +------+
Figure 8: BGP Hybrid Flex-Algo Aware transport Transport CAR path Path
* The following description applies to the reference topology above:
- IGP FA 128 is only enabled in Core (e.g. core (e.g., WAN network), mapped
to C1. Access network domain only has Base Algo 0.
- Egress PE E2 advertises a VPN route RD:V/v colored with Color-
EC C1 to steer traffic via BGP transport CAR (E2, C1). VPN
route propagates via service RRs to ingress PE E1.
- BGP CAR route (E2, C1) with next hop, label index index, and label as
shown above are advertised through border routers in each
domain. When a an RR is used in the domain, ADD-PATH is enabled
to advertise multiple available paths.
- Local policy on 231 and 232 maps intent C1 to resolve CAR route
next hop over IGP Base Algo 0 in right access domain. The BGP
CAR label swap entry is installed that goes over Base Algo 0
LSP to next hop. Updates AIGP metric is updated to reflect Base Algo 0
metric to next hop with an additional penalty (+1000).
- On 121 and 122, CAR route (E2, C1) next hop learnt from Core
domain is resolved over IGP FA 128. The BGP CAR label swap
entry is installed that goes over FA 128 LSP to next hop
providing intent in Core IGP domain.
- Ingress PE E1 learns CAR route (E2, C1). It maps intent C1 to
resolve CAR route next hop over IGP Base Algo 0. It steers
colored VPN route RD:V/v via (E2, C1) C1).
* Important:
- IGP Flex-Algo 128 top label provides intent in Core domain.
- BGP CAR label (e.g. (e.g., 168002) carries intent from PEs PEs, which is
realized in core Core domain.
A.3.2. Provide intent Intent for service flows only Service Flows Only in core domain Core Domain over TE
tunnel mesh
Tunnel Mesh
RD:1/8 via E2
+-----+ vpn label: 30030 +-----+
...... |S-RR1| <..................................|S-RR2| <.......
: +-----+ Color C1 +-----+ :
: :
: :
: :
+-:-----------------------+----------------------+-----------------:-+
| : | | : |
| : | | : |
| : (E2,C1) via 121 | (E2,C1) via 231 | (E2,C1) via E2 : |
| : L=242003,AIGP=1110+---+L=242002,AIGP=1010+---+ L=0x3 : |
| : |-------------------|121|<-----------------|231|<-------------|: |
| : V +---+ TE tunnel(231) +---+ |: |
|----+ | | +---|
| E1 | | | |E2 |
|----+(E2,C1) via 122 | (E2,C1) via 232 | (E2,C1) via E2+---|
| ^ L=242004,AIGP=1210+---+L=242001,AIGP=1020+---+ L=0x3 | |
| |---------------- |122|<-----------------|232|<-------------| |
| +---+ TE tunnel(232) +---+ |
| | | |
| | | |
| IS-IS/LDP | IS-IS/RSVP-TE | IS-IS/LDP |
| Access 0 | Core | Access 1 |
+-------------------------+----------------------+-------------------+
iPE iABR eABR ePE
---------direction of traffic-------->
+------+ +------+
|240121| |241231|
+------+ +------+
+------+ +------+ +------+
|242003| |242002| |240002|
+------+ +------+ +------+
+------+ +------+ +------+
|30030 | |30030 | |30030 |
+------+ +------+ +------+
Figure 9: BGP CAR over TE tunnel mesh Tunnel Mesh in core network Core Network
* The following description applies to the reference topology above:
- RSVP-TE MPLS tunnel mesh is configured only in core (e.g. (e.g., WAN
network). Access only has IS-IS/LDP. (Figure (The figure does not
show all TE tunnels). tunnels.)
- Egress PE E2 advertises a VPN route RD:V/v colored with Color-
EC C1 to steer traffic via BGP transport CAR (E2, C1). VPN
route propagates via service RRs to ingress PE E1.
- BGP CAR route (E2, C1) with next hops and labels as shown above
is advertised through border routers in each domain. When a an
RR is used in the domain, ADD-PATH is enabled to advertise
multiple available paths.
- Local policy on 231 and 232 maps intent C1 to resolve CAR route
next hop over best-effort LDP LSP in access domain 1. The BGP
CAR label swap entry is installed that goes over LDP LSP to
next hop. AIGP metric is updated to reflect best-effort metric
to next hop with an additional penalty (+1000).
- Local policy on 121 and 122 maps intent C1 to resolve CAR route
next hop in Core domain over RSVP-TE tunnels. The BGP CAR
label swap entry is installed that goes over a TE tunnel to
next hop providing intent in Core domain. AIGP metric is
updated to reflect TE tunnel metric.
- Ingress PE E1 learns CAR route (E2, C1). It maps intent C1 to
resolve CAR route's next hop over best-effort LDP LSP in Access access
domain 0. It steers colored VPN route RD:V/v via (E2, C1).
* Important:
- RSVP-TE tunnel LSP provides intent in Core domain.
- Dynamic BGP CAR label carries intent from PEs PEs, which is
realized in core Core domain by resolution via RSVP-TE tunnel.
A.4. Transit network domains that do not support Network Domains That Do Not Support CAR
* In a brownfield deployment, color-aware paths between two PEs may
need to go through a transit domain that does not support CAR.
Examples of such a brownfield network include an MPLS LDP network
with IGP best-effort, or a BGP-LU based multi-domain network. network based on BGP-LU.
An MPLS LDP network with best-effort IGP can adopt the above
scheme in Section Appendix A.3. Below is the example scenario for BGP LU.
* Reference topology:
E1 --- BR1 --- BR2 ......... BR3 ---- BR4 --- E2
Ci <----LU----> Ci
Figure 10: BGP CAR not supported Not Supported in transit domain Transit Domain
- Network between BR2 and BR3 comprises of multiple BGP-LU hops
(over IGP-LDP domains).
- E1, BR1, BR4 BR4, and E2 are enabled for BGP CAR, with Ci colors.
- BR1 and BR2 are directly connected; BR3 and BR4 are directly
connected.
* BR1 and BR4 form an over-the-top peering (via RRs as needed) to
exchange BGP CAR routes.
* BR1 and BR4 also form direct BGP-LU sessions to BR2 and BR3 BR3,
respectively, to establish labeled paths between each other
through the BGP-LU network. The sessions may be eBGP or iBGP.
* BR1 recursively resolves the BGP CAR next hop for CAR routes
learnt from BR4 via the BGP-LU path to BR4.
* BR1 signals the transport discontinuity to E1 via the AIGP TLV, so
that E1 can prefer other paths if available.
* BR4 does the same in the reverse direction.
* Thus, the color-awareness color awareness of the routes routes, and hence the paths in
the data plane plane, are maintained between E1 and E2, even if the
intent is not available within the BGP-LU island.
* A similar design can be used for going over network islands of
other types.
A.5. Resource Avoidance using Using BGP CAR and IGP Flex-Algo
This example illustrates a case of resource avoidance within a domain
for a multi-domain color-aware path.
+-------------+ +-------------+
| | | | V/v with C1
|----+ |------| +----|/
| E1 | | | | E2 |\
|----+ | | +----| W/w with C2
| |------| IGP FA128 |
| IGP FA128 | | IGP FA129 |
| Domain 1 | | Domain 2 |
+-------------+ +-------------+
Figure 11: BGP CAR resolution Resolution over IGP FLex-Algo Flex-Algo for resource
avoidance Resource
Avoidance in a domain Domain
* C1 and C2 represent the following two unique intents in the multi-
domain network:
- C1 is mapped to "minimize IGP metric", and
- C2 is mapped to "minimize IGP metric and avoid resource R".
* Resource R represents link(s) or node(s) to be avoided.
* Flex-Algo FA128 in Domain 2 is mapped to "minimize IGP metric" metric",
and hence to C1.
* Flex-Algo FA129 in Domain 2 is mapped to "minimize IGP metric and
avoid resource R" R", and hence to C2.
* Flex-Algo FA128 in Domain 1 is mapped to "minimize IGP metric"
i.e.,
- There
(i.e., there is no resource R to be avoided in Domain 1, hence
both C1 and C2 are mapped to FA128. FA128).
* E1 receives the following two service routes from E2:
- V/v with BGP Color-EC C1, and
- W/w with BGP Color-EC C2.
* E1 has the following color-aware paths:
- (E2, C1) provided by BGP CAR with the following per-domain
resolution:
o Domain1: Domain 1: over IGP FA128, and
o Domain2: Domain 2: over IGP FA128.
- (E2, C2) provided by BGP CAR with the following per-domain
resolution:
o Domain1: Domain 1: over IGP FA128, and
o Domain2: Domain 2: over IGP FA129 (avoiding resource R).
* E1 automatically steers the received service routes as follows:
- V/v via (E2, C1) provided by BGP CAR.
- W/w via (E2, C2) provided by BGP CAR.
Observations:
* C1 and C2 are realized over a common intra-domain intent (FA128)
in one domain and distinct intents in another domain as required.
* 32-bit Color space provides flexibility in defining a large number
of intents in a multi-domain network. They may be efficiently
realized by mapping to a smaller number of intra-domain intents in
different domains.
A.6. Per-Flow Steering over CAR routes Routes
This section provides an example of ingress PE per-flow steering as
defined in section Section 8.6 of [RFC9256] onto BGP CAR routes.
The following description applies to the reference topology in
Figure 6:
* Ingress PE E1 learns best-effort BGP LU route E2.
* Ingress PE E1 learns CAR route (E2, C1), C1 is mapped to "low
delay".
* Ingress PE E1 learns CAR route (E2, C2), C2 is mapped to "low
delay and avoid resource R".
* Ingress PE E1 is configured to instantiate an array of paths to E2
where entry 0 is the BGP LU path to next hop, color C1 is the
first entry entry, and color C2 is the second entry. The index into the
array is called a Forwarding Class (FC). The index can have
values 0 to 7, especially when derived from the MPLS TC bits
[RFC5462].
* E1 is configured to match flows in its ingress interfaces (upon
any field such as Ethernet destination/source/VLAN/TOS or IP
destination/source/DSCP or transport ports ports, etc.) and color them
with an internal per-packet FC variable (0, 1 1, or 2 in this
example).
* This array is presented as a composite candidate path of SR policy
(E2, C100) and acts as a container for grouping constituent paths
of different colors/best-effort. This representation provides
automated steering for services colored with Color-EC C100 via
paths of different colors. Note that Color-EC C100 is used as
indirection to the composite policy configured on ingress PE.
* Egress PE E2 advertises a VPN route RD:V/v with Color-EC C100 to
steer traffic via composite SR policy (E2, C100); i.e., C100) (i.e., FC array
of paths. paths).
E1 receives three packets K, K1, and K2 on its incoming interface.
These three packets matches match on the VPN route which that recurses on E2. E1
colors these 3 packets respectively with forwarding-class forwarding class 0, 1, and
2. 2,
respectively.
As a result result:
* E1 forwards K along the best-effort path to E2 (i.e., for the MPLS
data plane, it pushes the best-effort label of E2).
* E1 forwards K1 along the (E2, C1) BGP CAR route.
* E1 forwards K2 along the (E2, C2) BGP CAR route.
A.7. Advertising BGP CAR routes Routes for shared Shared IP addresses Addresses
+-------------+ +--------------+
| | | +----|
| |------| | E2 |(IP1)
|----+ | | +----|
| E1 | | | Domain 2 |
|----+ | +--------------+
| | +--------------+
| | | +----|
| Domain 1 |------| | E3 |(IP1)
+-------------+ | +----|
| Domain 3 |
+--------------+
Figure 12: BGP CAR advertisements Advertisements for shared Shared IP addresses Addresses
This example describes a case where a route for the same transport IP
address is originated from multiple nodes in different network
domains.
One use of this scenario is an Anycast anycast transport service, where
packet encapsulation (e.g., LSP) may terminate on any one among a set
of nodes. All the nodes are capable of forwarding the inner payload,
typically via an IP lookup in the global table for Internet routes.
A couple of variations of the use-case use case are described in the example
below.
One node is shown in each domain, but there will be multiple nodes in
practice for redundancy.
Example-1:
Example 1: Anycast with forwarding to nearest nearest:
* Both E2 (in egress domain 2) and E3 (in egress domain 3) advertise
Anycast (shared) IP (IP1, C1) with same label Label L1.
* An ingress PE E1 receives by default the best path(s) for (IP1,
C1) propagated through BGP hops across the network.
* The paths to (IP1, C1) from E2 and E3 may merge at a common node
along the path to E1, forming equal cost multipaths or active-
backup paths at that node.
* Service route V/v is advertised from egress domains D2 and D3 with
color C1 and next hop IP1.
* Traffic for V/v steered at E1 via (IP1, C1) is forwarded to either
E2 or E3 (or both) as determined by routing along the network
(nodes in the path).
Example-2:
Example 2: Anycast with egress domain visibility at ingress PE PE:
* E2 advertises (IP1, C1) and E3 advertises (IP1, C2) CAR routes for
the Anycast IP IP1. C1 and C2 are colors assigned to distinguish
the egress domains originating the routes to IP1.
* An ingress PE E1 receives the best path(s) propagated through BGP
hops across the network for both (IP1, C1) and (IP1, C2).
* The CAR routes (IP1, C1) and (IP1, C2) do not get merged at any
intermediate node, providing E1 control over path selection and
load-balancing of traffic across these two routes. Each route may
itself provide multipathing or Anycast anycast to a set of egress nodes.
* Service route V/v advertised from egress domains D2 and D3 with
colors C1 and C2 C2, respectively, but with same next hop IP1.
* E1 will resolve and steer V/v path from D2 via (IP1, C1) and path
from D3 via (IP2, C2). E1 will load-balance traffic to V/v across
the two paths as determined by a local load-balancing policy.
* Traffic for colored service routes steered at E1 is forwarded to
either E2 or E3 (or load-balanced across both) as determined by
E1.
In above example, D2 and D3 belonged to the same color or
administrative domain. If D2 and D3 belong to different color
domains, the domains will coordinate the assignment of colors with
shared IP IP1 so that they do not cause conflicts. For instance, in
Example-1:
Example 1:
* D2 and D3 may both use C1 for the same intent when they originate
CAR route for IP1.
- In this case, neither D2 nor D3 will reuse C1 for some other
intent.
* Alternatively, D2 may use C2 and D3 may use C3 for originating a
CAR route for IP1 for the same intent.
- In this case, D2 will not use C3 for originating CAR route for
IP1 for some other intent. Similarly, D3 will not use C2 for
originating CAR route for IP1 for some other intent.
Appendix B. Color Mapping Illustrations
There are a variety of deployment scenarios that arise when different
color mappings are used in an inter-domain environment. This section
attempts to enumerate them and provide clarity into the usage of the
color related
color-related protocol constructs.
B.1. Single color domain containing network domains Color Domain Containing Network Domains with N:N color
distribution Color
Distribution
* All network domains (ingress, egress egress, and all transit domains) are
enabled for the same N colors.
- A color may of course be realized by different technologies in
different domains as described above.
* The N intents are both signaled end-to-end via BGP CAR routes; routes, as
well as realized in the data plane.
* Appendix A.1 is an example of this case.
B.2. Single color domain containing network domains Color Domain Containing Network Domains with N:M color
distribution Color
Distribution
* Certain network domains may not be enabled for some of the colors
used for end-to-end intents, but may still be required to provide
transit for routes of those colors.
* When a (E, C1) route traverses a domain where color C1 is not
available, the operator may decide to use a different intent of
color C2 that is available in that domain to resolve the next hop
and establish a path through the domain.
- The next hop next-hop resolution may occur via paths of any intra-domain
protocol or even via paths provided by BGP CAR.
- The next hop next-hop resolution color C2 may be defined as a local
policy at ingress or transit nodes of the domain.
- It may also be automatically signaled from egress border nodes
by attaching a Color-EC with value C2 to the BGP CAR routes.
* Hence, routes of N end-to-end colors may be resolved over paths
from a smaller set of M colors in a transit domain, while
preserving the original color-awareness color awareness end-to-end.
* Any ingress PE that installs a service (VPN) route with a color
C1, C1
must have C1 enabled locally to install IP routes to (E, C1) and
resolve the service route's next hop.
* A degenerate variation of this scenario is where a transit domain
does not support any color. Appendix A.3 describes an example of
this case.
Illustration for N end to end end-to-end intents over fewer M intra-domain
intents:
RD:V/v via E2 Color-EC: 100
RD:W/w via E2 Color-EC: 200
+-----+ RD:X/x via E2 Color-EC: 300 +-----+
...... |S-RR1| <..................................|S-RR2| <........
: +-----+ RD:Y/y via E2 Color-EC: 400 +-----+ :
: :
: :
: :
+-:---------------------+---------------------+----------------------:-+
| : | | : |
| | | |
| (E2,100) via 121 | (E2,100) via 231 | (E2,100) via E2 |
| Color-EC: 1,10 | Color-EC: 1,10 | Color-EC: 1,10 |
| | | |
| (E2,200) via 121 | (E2,200) via 231 | (E2,200) via E2 |
| Color-EC: 1,20 | Color-EC: 1,20 | Color-EC: 1,20 |
| <--- <---- |
| (E2,300) via 121 | (E2,300) via 231 | (E2,300) via E2 |
| Color-EC: 2,30 | Color-EC: 2,30 | Color-EC: 2,30 |
| | | |
| (E2,400) via 121 | (E2,400) via 231 | (E2,400) via E2 |
| Color-EC: 2,40 | Color-EC: 2,40 | Color-EC: 2,40 |
| | | |
| +===+ +===+ |
|====+ | |-------C10-------| | +=====|
| |-------C1-------| |-------C20-------| |-------C1-------| |
| E1 | |121| |231| | E2 |
| |-------C2-------| |-------C30-------| |-------C2-------| |
|====+ | |-------C40-------| | +=====|
| +===+ +===+ |
| C1=FA132 | C10=FA128 | C1=FA132 |
| C2=FA133 | C20=FA129 | C2=FA133 |
| | C30=FA130 | |
| | C40=FA131 | |
| | | |
| IS-IS SR | IS-IS SR | IS-IS SR |
| ACCESS | CORE | ACCESS |
+-----------------------+---------------------+------------------------+
iPE iABR eABR ePE
Figure 13: N:M illustration Illustration
* The following description applies to the reference topology above:
- Core domain provides 4 intra-domain intents as described below:
o FA128 mapped to C10,
o FA129 mapped to C20,
o FA130 mapped to C30, and
o FA131 mapped to C40.
- Access domain provides the following 2 intra-domain intents:
o FA132 mapped to C1, and
o FA133 mapped to C2 C2.
- Operator defines the following 4 BGP CAR end to end end-to-end intents as
below:
o CAR color C100 that resolves on C1 in access and C10 in core Core
domain,
o CAR color C200 that resolves on C1 in access and C20 in core Core
domain,
o CAR color C300 that resolves on C2 in access and C30 in core Core
domain, and
o CAR color C400 that resolves on C2 in access and C40 in core Core
domain.
- E2 may originate BGP CAR routes with multiple BGP Color-ECs as
shown above. At each hop, CAR route's next hop is resolved
over the available intra-domain color. For example (E2, C100)
with BGP color ECs Color-ECs C1, C10 resolves over C1 at ABR 231, C10 at
ABR 121, and C1 at E1.
- Egress PE E2 advertises a VPN route RD:V/v colored with BGP
Color-EC C100 to steer traffic through FA 132 in access and FA
128 in core. It also advertises another VPN route RD:W/w
colored with BGP Color-EC C200 to steer traffic through FA 132
in access and FA 129 in core.
* Important:
- End-to-end (BGP CAR) colors can be decoupled from intra-domain
transport colors.
- Each end-to-end BGP CAR color is a combination of various
intra-domain colors or intents.
- Combination can be expressed by local policy at ABRs or by
attaching multiple BGP Color-ECs at origination point of BGP
CAR route.
- Service traffic is steered into suitable CAR color to use the
most granular intent in a domain multiple hops away from
ingress PE.
- Consistent reuse of standard color based color-based resolution mechanism
at both service and transport layers.
B.3. Multiple color domains Color Domains
When the routes are distributed between domains with different color-
to-intent mapping schemes, both N:N and N:M cases are possible.
Although an N:M mapping is more likely to occur.
Reference topology:
D1 ----- D2 ----- D3
C1 C2 C3
Figure 14: Multiple color domains Color Domains
* C1 in D1 maps to C2 in D2 and to C3 in D3.
* BGP CAR is enabled in all three color domains.
The reference topology above is used to elaborate on the design
described in Section 2.8
When the route originates in color domain D1 and gets advertised to a
different color domain D2, the following procedures apply:
* The NLRI of the BGP CAR route is preserved end to end, i.e., end (i.e., route
is (E, C1). C1)).
* A BR of D1 attaches LCM-EC with value C1 when advertising to a BR
in D2.
* A BR in D2 receiving (E, C1) maps C1 in received LCM-EC to local
color, say C2.
- A BR in D2 may receive (E, C1) from multiple D1 BRs BRs, which
provide equal cost or primary/backup paths.
* Within D2, this LCM-EC value of C2 is used instead of the Color in
CAR route NLRI (E, C1). This applies to all procedures described
in the earlier section for a single color domain, such as next-hop
resolution and service steering.
* A colored service route V/v originated in color domain D1 with
next hop E and Color-EC C1 will also have its color extended-
community Color-EC value re-mapped re-
mapped to C2, typically at a service RR.
* On an ingress PE in D2, V/v will resolve via C2.
* When a BR in D2 advertises the route to a BR in D3, the same
process repeats.
Appendix C. CAR SRv6 Illustrations
C.1. BGP CAR SRv6 locator reachability hop by hop distribution Locator Reachability Hop-by-Hop Distribution
RD:V/v via E2
+-----+ SRv6SID=B:C11:2:DT4:: +-----+
...... |S-RR1| <..................................|S-RR2| <.....
: +-----+ +-----+ :
: :
: :
: AS2 AS1 :
+-:------------------------------------+ +--------------:--+
| : | | : |
| : B:C11::/32 via IP1 | | : |
| : +-----+ LCM=C1, AIGP=10 | | : |
| : | TRR |<.............. | | : |
| : +-----+<.......... : | | : |
| : : B:C11::/32 : : | | : |
| : : via IP2 : : | | : |
| : : LCM=C1,AIGP=10: : | | : |
| : ......... : : : | B:C11::/32 | : |
| : : : : : | via 231 | +-----|
| : : : : : | LCM=C1 | | E2 |
: : +---+ : +---+ : : | AIGP=10 | +-----|
| : : |P11|<.:..>|P13| : +----+ +---+ : |
| : : +---+ : +---+ : | 121|-----IP1|231| : |
| V V : : +----+ eBGP +---+ : |
|----+ : : | | +-----|
| E1 | +---+ : +---+ : | | | En |
|----+ |P12|<.:..>|P14| : | | +-----|
| +---+ +---+ : +----+ eBGP +---+ |
| IPv6 FIB: ...| 122|-----IP2|232| |
| B:C11::/32 via IP1 +----+ +---+ |
| via IP2 | B:C11::/32 | |
| | via 232 | |
| | LCM=C1 | |
| | AIGP=10 | |
| IS-ISv6 | | IS-ISv6 |
| FA 128 (B:C12::/32) | |FA128(B:C11::/32)|
| FA 0 (B:02::/32) | |FA0 (B:01::/32) |
+--------------------------------------+ +-----------------+
iPE ASBR ASBR ePE
Figure 15
The topology above is an example to illustrate the BGP CAR SRv6
locator prefix route based route-based design (Routed Service SID:
Section 7.1.1), (Section 7.1.1) with hop by hop hop-by-hop
IPv6 routing within and between domains.
* Multi-AS network with eBGP CAR session between ASBRs.
* Transport RR (TRR) peers with P, BR BR, and PE clients within an AS
to propagate CAR prefixes. AddPath ADD-PATH is enabled to propagate
multiple paths.
* IS-IS (IGP) Flex-Algo 128 for SRv6 is running in each AS (AS may
consist of multiple IGP domains), where the following steps apply:
- Prefix B:C11::/32 summarizes Flex-Algo 128 block in AS1 for the
given intent. Node locators in the egress domain are sub-
allocated from the block for the given intent.
- Similarly, Prefix B:C12::/32 summarizes Flex-Algo 128 block in
AS2.
- Per Flex-Algo external subnets for eBGP next hops IP1 and IP2
are distributed in IS-IS within AS2.
* BGP CAR prefix route B:C11::/32 with LCM C1 is originated by AS1
BRs 231 and 232 on eBGP sessions to AS2 BRs 121 and 122.
* ASBR 121 and 122 propagate the route in AS2 to all the P, ABRs ABRs,
and PEs through transport RR.
* Every router in AS2 resolves BGP CAR prefix B:C11::/32 next hops
IP1 and IP2 in IS-ISv6 Flex-Algo 128 and programs B:C11::/32
prefix in global IPv6 forwarding table.
* AIGP attribute influences BGP CAR route best path decision.
* Egress PE E2 advertises a VPN route RD:V/v with SRv6 service Service SID
B:C11:2:DT4::. Service SID is allocated by E2 from its locator of
color C1 intent.
* Ingress PE E1 learns (via service RRs S-RR1 and S-RR2) VPN route
RD:V/v with SRv6 SID B:C11:2:DT4::.
* Service traffic encapsulated with SRv6 Service SID B:C11:2:DT4::
is natively steered hop by hop along IPv6 routed path to
B:C11::/32 provided by BGP CAR in AS2.
* Encapsulated service traffic is natively steered along IPv6 routed
path to B:C11::/32 provided by IS-ISv6 Flex-Algo 128 in AS1.
* Design applies to multiple ASNs. BGP next hop is rewritten across
a
an eBGP hop.
Important:
* No tunneling/encapsulation on Ingress ingress PE and BRs for BGP CAR
provided transport.
* Uses longest prefix match of SRv6 service Service SID to BGP CAR IP
prefix. No mapping to labels/SIDs, instead use of simple IP based IP-based
forwarding.
Packet forwarding forwarding:
@E1: IPv4 VRF V/v => H.Encaps.red <B:C11:2:DT4::> => forward Forward based
on B:C11::/32
@P*: IPv6 table: B:C11::/32 => forward Forward to interface, NH
@121: IPv6 Table: B:C11::/32 => forward Forward to interface, NH
@231: IPv6 table: B:C11:2::/48 :: => forward Forward via IS-ISv6 FA path to E2
@231: IPv6 Table B:C11:2::/48 => forward Forward via IS-ISv6 FA path to E2
@E2: My SID table B:C11:2:DT4:: =>pop => Pop the outer header and lookup look up
the inner DA in the VRF
C.2. BGP CAR SRv6 locator reachability distribution Locator Reachability Distribution with encapsulation Encapsulation
RD:V/v via E2
+-----+ SRv6SID=B:C11:2:DT4:: +-----+
...... |S-RR1| <..................................|S-RR2| <.......
: +-----+ +-----+ :
: :
: :
: :
+-:-----------------------+----------------------+------------------:--+
| : | | : |
| : | | : |
| : B:C11::/32 via 121 | B:C11::/32 via 231 | : |
| : SID=B:C13:121:END:: | SID=B:C12:231:END:: | : |
| : LCM=C1,AIGP=110 +---+LCM=C1 AIGP=10 +---+ : |
| : |-------------------|121|<-----------------|231|<-------------| : |
| : V +---+ +---+ | : |
|----+ | | +-----|
| E1 | | | | E2 |
|----+ | | +-----|
| ^ | | : |
| | | | : |
| | | | +-----|
| | | | | En |
| | | | +-----|
| | +---+ +---+ | |
| |---------------- |122|<-----------------|232|<-------------| |
| +---+ +---+ |
| B:C11::/32 via 122 | B:C11::/32 via 232 | |
| SID=B:C13:122:END:: | SID=B:C12:232:END:: | |
| LCM=C1 AIGP=120 | LCM=C1 AIGP=20 | |
| | | |
| IS-ISv6 | IS-ISv6 | IS-ISv6 |
| FA 128 (B:C13::/32) | FA 128 (B:C12::/32) | FA128 (B:C11::/32) |
| FA 0 (B:03::/32) | FA 0 (B:02::/32) | FA1 0 (B:01::/32) |
+-------------------------+----------------------+---------------------+
iPE iABR eABR ePE
Figure 16
The topology above is an example to illustrate the BGP CAR SRv6
locator prefix route based route-based design (Routed Service SID:
Section 7.1.1), (Section 7.1.1) with intra-domain
encapsulation. The example shown is iBGP, but also applies to eBGP
(multi-AS).
* IGP Flex-Algo 128 is running in each domain, where where:
- Prefix B:C11::/32 summarizes Flex-Algo 128 block in egress
domain for the given intent. Node locators in the egress
domain are sub-allocated from the block.
- Prefix B:C12::/32 summarizes FA128 block in transit domain.
- Prefix B:C13::/32 summarizes FA128 block in ingress domain.
* BGP CAR route B:C11::/32 is originated by ABRs 231 and 232 with
LCM C1. Along the propagation path, border routers set next-hop-
self and appropriately update the intra-domain encapsulation
information for the C1 intent. For example, 231 and 121 signal
SRv6 SID of END End behavior [RFC8986] allocated from their respective
locators for the C1 intent. (Note: IGP Flex-Algo is shown for
intra-domain path, but SR-Policy may also provide the path as
shown in Appendix C.3). C.3.)
* AIGP attribute influences BGP CAR route best path decision.
* Egress PE E2 advertises a VPN route RD:V/v with SRv6 service Service SID
B:C11:2:DT4::. Service SID is allocated by E2 from its locator of
color C1 intent.
* Ingress PE E1 learns CAR route B:C11::/32 and VPN route RD:V/v
with SRv6 SID B:C11:2:DT4::.
* Traffic encapsulated with SRv6 Service SID B:C11:2:DT4:: is
steered along IPv6 routed path provided by BGP CAR IP prefix route
to locator B:C11::/32.
Important
Important:
* Uses longest prefix match of SRv6 service Service SID to BGP CAR prefix.
No
There is no mapping labels/SIDs, instead labels/SIDs; there is simple IP based forwarding. IP-based
forwarding instead.
* Originating domain PE locators of the given intent can be
summarized on transit BGP hops eliminating per PE state on border
routers.
Packet forwarding forwarding:
@E1: IPv4 VRF V/v => H.Encaps.red <B:C13:121:END::, B:C11:2:DT4::>
@121: My SID table: B:C13:121:END:: => Update DA with B:C11:2:DT4::
@121: IPv6 Table: B:C11::/32 => H.Encaps.red <B:C12:231:END::>
@231: My SID table: B:C12:231:END:: => Remove IPv6 header;
Inner DA B:C11:2:DT4::
@231: IPv6 Table B:C11:2::/48 => forward Forward via IS-ISv6 FA path to E2
@E2: My SID table B:C11:2:DT4:: =>pop => Pop the outer header and lookup look up
the inner DA in the VRF
C.3. BGP CAR (E, C) route distribution Route Distribution for steering non-routed service Steering Non-Routed Service
SID
RD:V/v via E2
+-----+ SRv6SID: B:01:2:DT4:: +-----+
...... |S-RR1| <..................................|S-RR2| <.......
: +-----+ Color C2 +-----+ :
: :
: +-----+ (E2,C2) via 231 :
: -----------------| TRR |-------------------| :
:| +-----+ SID=B:C21:2:B6:: | :
+-:|---------------------+---------------------|+------------------:--+
| :| | || : |
| :| | || : |
| :| B:C21::/32 via 121 | B:C21::/32 via 231 ||SR policy(E2,C2) : |
| :| LCM=C2,AIGP=110 | LCM=C2 AIGP=10 ||BSID=B:C21:2:B6:: : |
| :| +---+ +---+ : |
| :|-------------------|121|<-----------------|231|<-------------| : |
| :V SR policy(121,C2) +---+SR policy(231,C2) +---+ | : |
|----+ | | +-----|
| E1 | | | | E2 |
|----+ | | +-----|
| ^ SR policy(122,C2) +---+SR policy(232,C2) +---+ | |
| |---------------- |122|<-----------------|232|<-------------| |
| B:C21::/32 via 121+---+B:C21::/32 via 232+---+ SR policy(E2,C2) |
| LCM=C2,AIGP=120 | LCM=C2 AIGP=20 | BSID=B:C21:2:B6:: |
| | | |
| IS-ISv6 | IS-ISv6 | IS-ISv6 |
| FA 0 (B:03::/32) | FA 0 (B:02::/32) | FA 0(B:01::/32) |
+------------------------+----------------------+---------------------+
iPE iABR eABR ePE
Figure 17
The topology above is an example to illustrate the BGP CAR (E, C)
route based
route-based design (Section 7.1.2). The example is iBGP, but the
design also applies to eBGP (multi-AS).
* SR policy (E2, C2) provides given intent in egress domain.
- SR policy (E2, C2) with segments <B:01:z:END::, B:01:2:END::> B:01:2:END::>,
where z is the node id in egress domain.
* Egress ABRs 231 and 232 redistribute SR policy into BGP CAR Type-1
NLRI (E2, C2) to other domains, with SRv6 SID of End.B6 behavior.
This route is propagated to ingress PEs through transport Transport RR (TRR)
or inline with next hop unchanged. next-hop-unchanged.
* The ABRs also advertise BGP CAR prefix route (B:C21::/32)
summarizing locator part of SRv6 SIDs for SR policies of given
intent to different PEs in egress domain. BGP CAR prefix route
propagates through border routers. At each BGP hop, BGP CAR
prefix next-hop resolution triggers intra-domain transit SR policy
(C2, CAR next hop). For example:
- SR policy (231, C2) with segments <B:02:y:END::,
B:02:231:END::>, and
- SR policy (121, C2) with segments <B:03:x:END::,
B:03:121:END::>,
- where x and y are node ids within the respective domains.
* Egress PE E2 advertises a VPN route RD:V/v with Color-EC C2.
* Ingress PE E1 steers VPN route from E2 onto BGP CAR route (E2, C2)
that results in H.Encaps.red of SRv6 transport SID B:C21:2:B6::
and SRv6 service Service SID as last segment in IPv6 header.
* IPv6 destination B:C21:2:B6:: match on CAR prefix B:C21::/32 that
steers the packet into intra-domain (intent-aware) SR Policy on
ingress PE E1 and ABR 121.
* IPv6 packet destination B:C21:2:B6:: lookup in mySID table on ABR
231 or 232 results in END.B6 behavior (i.e., push of policy
segments to E2).
Important
Important:
* Ingress PE steers services via (E, C) CAR route as per [RFC9256].
* In data plane (E, C) C), resolution results in IPv6 header
destination being SRv6 SID of END.B6 behavior whose locator is of
given intent on originating ABRs.
* CAR IP prefix route along the transit path provides simple LPM Longest
Prefix Match (LPM) IPv6 forwarding along the transit BGP hops.
* CAR NLRI Type-2 prefix summarizes binding SIDs of all SR policies
on originating ABR of a given intent to different PEs in egress
domain. This eliminates per PE state on transit routers.
Packet forwarding forwarding:
@E1: IPv4 VRF V/v => H.Encaps.red <B:C21:2:B6::, B:0:E2:DT4::>
H.Encaps.red <SR policy (C2,121) sid list>
@121: My SID table: B:03:121:END:: => Remove outer IPv6 header;
Inner DA B:C21:2:B6::
@121: IPv6 Table: B:C21::/32 => H.Encaps.red <SR Policy (C2,231) sid
list>
@231: My SID table: B:02:231:END:: => Remove outer IPv6 header;
Inner DA B:C21:2:B6::
@231: MySIDtable B:C21:2:B6:: => H.Encaps.red <SR Policy (C2,E2) sid
list>
@E2: IPv6 Table B:0:2:DT4:: =>pop => Pop the outer header and lookup look up the
inner DA in the VRF
Appendix D. CAR SAFI NLRI update packing efficiency calculation Update Packing Efficiency Calculation
CAR SAFI NLRI encoding is optimized for update packing. It allows
per route
per-route information (for example example, label, label index index, and SRv6 SID
encapsulation data) to be carried in the non-key TLV part of NLRI.
This allows multiple NLRIs to be packed in a single update message
when other attributes (including LCM-EC LCM-EC, when present) are shared.
The table below shows a theoretical analysis calculated from observed
BGP update message size in operational networks. It compares total
BGP data on the wire for CAR SAFI and [RFC8277] style encoding in
MPLS label (CASE A), SR extension with MPLS (per-prefix label index
in Prefix-SID attribute) [RFC8669] (CASE B) and SRv6 SID (CASE C)
cases.
Scenarios The packing scenarios considered are as follows:
* the ideal packing (maximum case (where the maximum number of routes are packed to
the update message limit of 4k bytes),
* the practical deployment case with of average packing (5 (where 5 routes share a set
of BGP path attributes attributes, and hence are packed in a single update message)
message), and worst-case
* the worst case of no packing (each (where each route is in a separate
update message).
----------------+--------------+----------------+-----------------------
+=============+=========+===========+============================+
| Encoding | BGP CAR |RFC-8277 style | [RFC8277] | Result |
| | NLRI | style | |
| | | NLRI |NLRI |
----------------+--------------+----------------+----------------------- |
+=============+=========+===========+============================+
| CASE A: Label | |
+=============+=========+===========+============================+
| (Ideal) | 27.5 MB | 26 MB |
+--------------+----------------+ No degradation from |
| | | | [RFC8277] like encoding. |
+-------------+---------+-----------+ |
| (Practical) | 86 MB | 84 MB | RFC8277 like encoding
+--------------+----------------+
(No packing) |
+-------------+---------+-----------+ |
| (Worst; no | 325 MB | 324 MB |
----------------+--------------+----------------+----------------------- |
| packing) | | | |
+=============+=========+===========+============================+
| CASE B: Label & Label-index |
+=============+=========+===========+============================+
| (Ideal) | 42 MB | 339 MB | CAR SAFI encoding is more
& Label-index |
| | | Packing not | efficient by 88% in
(Ideal) the | 42 MB
| possible | | not | best case and 71% in
+--------------+----------------+ the |
| | | possible | average case over |
| | | | [RFC8277] style encoding |
| | | | (which precludes packing). |
+-------------+---------+-----------+ |
| (Practical) | 99 MB | 339 MB | RFC8277 style encoding |
| | | Packing | |
| | | not | (which precludes |
| | | possible | packing)
+--------------+----------------+
(No packing) |
+-------------+---------+-----------+ |
| (Worst; no | 339 MB | 339 MB | |
| packing) | | | |
+=============+=========+===========+============================+
|
----------------+--------------+----------------+----------------------- CASE C: SRv6 SID| SID |
+=============+=========+===========+============================+
| Results are similar to (Ideal) | 49 MB | 378 MB | SR MPLS Results are similar to the |
| | | | SR-MPLS case. |
| | | | Transposition provides
+--------------+----------------+ a |
| | | | further 20% reduction in |
| | | | BGP data. |
+-------------+---------+-----------+ |
| (Practical) | 115 MB | 378 MB | in BGP data.
+--------------+----------------+
(No packing) |
+-------------+---------+-----------+ |
| (Worst; no | 378 MB | 378 MB |
----------------+--------------+----------------+-----------------------
Figure 18: |
| packing) | | | |
+-------------+---------+-----------+----------------------------+
Table 5: Summary of ideal, practical the Ideal, Practical, and no-packing Worst Cases of
Packing BGP data in
each case
Analysis Data
This analysis considers 1.5 million routes (5 colors across 300k
endpoints)
endpoints).
CASE A: BGP data exchanged for non SR MPLS case the non-SR-MPLS case:
Consider 200 bytes of shared attributes
CAR SAFI signal Label in non-key TLV part of NLRI
Each NLRI size for AFI 1 = 12(key) + 5(label) = 17 bytes
Ideal packing:
number of NLRIs in 4k update size = 223 (4k-200/17)
number of update messages of 4k size = 1.5 million/223 = 6726
Total BGP data on wire = 6726 * 4k = ~27.5MB
Practical packing (5 routes in update message) message):
size of update message = (17 * 5) + 200 = 285
Total BGP data on wire = 285 * 300k = ~86MB
No-packing case (1 route per update message) message):
size of update message = 17 + 200 = 217
Total BGP data on wire = 217 * 1.5 million = ~325MB
SAFI 128 8277 style encoding with label in NLRI
Each NLRI size for AFI 1 = 13(key) + 3(label) = 16 bytes
Ideal packing:
number of NLRIs in 4k update size = 237 (4k-200/16)
number of update messages of 4k size = 1.5 million/237 = ~6330
Total BGP data on wire = 6330 * 4k = ~25.9MB
Practical packing (5 routes in update message) message):
size of update message = (16 * 5) + 200 = 280
Total BGP data on wire = 280 * 300k = ~84MB
No-packing case (1 route per update message) message):
size of update message = 16 + 200 = 216
Total BGP data on wire = 216 * 1.5 million = ~324MB
CASE B: BGP data exchanged for SR label index index:
Consider 200 bytes of shared attributes
CAR SAFI signal Label in non-key TLV part of NLRI
Each NLRI size for AFI 1
= 12(key) + 5(label) + 9(Index) = 26 bytes
Ideal packing:
number of NLRIs in 4k update size = 146 (4k-200/26)
number of update messages of 4k size = 1.5 million/146 = 6726
Total BGP data on wire = 10274 * 4k = ~42MB
Practical packing (5 routes in update message)
size of update message = (26 * 5) + 200 = 330
Total BGP data on wire = 330 * 300k = ~99MB
No-packing case (1 route per update message)
size of update message = 26 + 200 = 226
Total BGP data on wire = 226 * 1.5 million = ~339MB
SAFI 128 8277 style encoding with label in NLRI
Each NLRI size for AFI 1 = 13(key) + 3(label) = 16 bytes
Ideal packing packing:
Not supported as label index is encoded in Prefix-SID
Attribute
attribute
Practical packing (5 routes in update message) message):
Not supported as label index is encoded in Prefix-SID
Attribute
attribute
No-packing case (1 route per update message) message):
size of update message = 16 + 210 = 226
Total BGP data on wire = 216 * 1.5 million = ~339MB
CASE C: BGP data exchanged with 128 bit single SRv6 SID SID:
Consider 200 bytes of shared attributes
CAR SAFI signal Label in non-key TLV part of NLRI
Each NLRI size for AFI 1 = 12(key) + 18(Srv6 SID) = 30 bytes
Ideal packing:
number of NLRIs in 4k update size = 126 (4k-200/30)
number of update messages of 4k size = 1.5 million/126 = ~12k
Total BGP data on wire = 12k * 4k = ~49MB
Practical packing (5 routes in update message) message):
size of update message
= (30 * 5) + 236 (including Prefix SID) Prefix-SID) = 386
Total BGP data on wire = 386 * 300k = ~115MB
No-packing case (1 route per update message) message):
size of update message = 12 + 236 (SID in Prefix SID) Prefix-SID) = 252
Total BGP data on wire = 252 * 1.5 million = ~378MB
SAFI 128 8277 style encoding with label in NLRI (No transposition)
Each NLRI size for AFI 1 = 13(key) + 3(label) = 16 bytes
Ideal packing packing:
Not supported as label index is encoded in Prefix-SID
Attribute
attribute
Practical packing (5 routes in update message) message):
Not supported as label index is encoded in Prefix-SID
Attribute
attribute
No-packing case (1 route per update message) message):
size of update message = 16 + 236 = 252
Total BGP data on wire = 252 * 1.5 million = ~378MB
BGP data exchanged with SRv6 SID 4 bytes transposition into SRv6 SID
TLV
TLV:
Consider 200 bytes of shared attributes
CAR SAFI signal Label in non-key TLV part of NLRI
Each NLRI size for AFI 1 = 12(key) + 6(Srv6 SID) = 18 bytes
Ideal packing:
number of NLRIs in 4k update size = 211 (4k-200/18)
number of update messages of 4k size = 1.5 million/211 = ~7110
Total BGP data on wire = 7110 * 4k = ~29MB
Practical packing (5 routes in update message) message):
size of update message
= (18 * 5) + 236 (including Prefix SID) Prefix-SID) = 326
Total BGP data on wire = 326 * 300k = ~98MB
No-packing case (1 route per update message) message):
size of update message
= 12 + 236 (SID in Prefix-SID Attribute) attribute) = 252
Total BGP data on wire = 252 * 1.5 million = ~378MB
Acknowledgements
The authors would like to acknowledge the invaluable contributions of
many collaborators towards the BGP CAR solution and this document in
providing input about use cases, participating in brainstorming and
mailing list discussions and in reviews of the solution and draft
revisions. In addition to the contributors listed in the
Contributors section, the authors would like to thank Robert Raszuk,
Bin Wen, Chaitanya Yadlapalli, Satoru Matsushima, Moses Nagarajah,
Gyan Mishra, Jorge Rabadan, Daniel Voyer, Stephane Litkowski, Hannes
Gredler, Jose Liste, Jakub Horn, Brent Foster, Dave Smith, Jiri
Chaloupka, Miya Kohno, Kamran Raza, Zafar Ali, Xing Jiang, Oleksander
Nestorov, Peter Psenak, Kaliraj Vairavakkalai, Natrajan Venkataraman,
Srihari Sangli, Ran Chen, and Jingrong Xie.
The authors also appreciate the detailed reviews and astute
suggestions provided by Sue Hares (as document shepherd), Jeff Haas,
Yingzhen Qu, and John Scudder that have greatly improved the
document.
Contributors
The following people gave substantial contributions to the content of
this document and should be considered as coauthors:
Clarence Filsfils
Cisco Systems
Belgium
Email: cfilsfil@cisco.com
Bruno Decraene
Orange
France
Email: bruno.decraene@orange.com
Luay Jalil
Verizon
United States of America
Email: luay.jalil@verizon.com
Yuanchao Su
Alibaba, Inc
Email: yitai.syc@alibaba-inc.com
Jim Uttaro
Individual
United States of America
Email: juttaro@ieee.org
Jim Guichard
Futurewei
United States of America
Email: james.n.guichard@futurewei.com
Ketan Talaulikar
Cisco Systems
India
Email: ketant.ietf@gmail.com
Keyur Patel
Arrcus, Inc
United States of America
Email: keyur@arrcus.com
Haibo Wang
Huawei Technologies
China
Email: rainsword.wang@huawei.com
Jie Dong
Huawei Technologies
China
Email: jie.dong@huawei.com
Additional contributors:
Dirk Steinberg
Lapishills Consulting Limited
Germany
Email: dirk@lapishills.com
Israel Means
AT&T
United States of America
Email: im8327@att.com
Reza Rokui
Ciena
United States of America
Email: rrokui@ciena.com
Authors' Addresses
Dhananjaya Rao (editor)
Cisco Systems
United States of America
Email: dhrao@cisco.com
Swadesh Agrawal (editor)
Cisco Systems
United States of America
Email: swaagraw@cisco.com