Internet DRAFT - draft-ietf-idr-bgp-car
draft-ietf-idr-bgp-car
IDR WorkGroup D. Rao, Ed.
Internet-Draft S. Agrawal, Ed.
Intended status: Experimental Cisco Systems
Expires: 5 August 2024 Co-authors
Section 13
2 February 2024
BGP Color-Aware Routing (CAR)
draft-ietf-idr-bgp-car-06
Abstract
This document describes a BGP based routing solution to establish
end-to-end intent-aware paths across a multi-domain service provider
transport network. This solution is called BGP Color-Aware Routing
(BGP CAR).
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Illustration . . . . . . . . . . . . . . . . . . . . . . 7
1.3. Requirements Language . . . . . . . . . . . . . . . . . . 10
2. BGP CAR SAFI . . . . . . . . . . . . . . . . . . . . . . . . 10
2.1. Data Model . . . . . . . . . . . . . . . . . . . . . . . 10
2.2. Extensible Encoding . . . . . . . . . . . . . . . . . . . 11
2.3. BGP CAR Route Origination . . . . . . . . . . . . . . . . 11
2.4. BGP CAR Route Validation . . . . . . . . . . . . . . . . 11
2.5. BGP CAR Route Resolution . . . . . . . . . . . . . . . . 12
2.6. AIGP Metric Computation . . . . . . . . . . . . . . . . . 13
2.7. Native MultiPath Capability . . . . . . . . . . . . . . . 14
2.8. BGP CAR Signaling through different Color Domains . . . . 14
2.9. Format and Encoding . . . . . . . . . . . . . . . . . . . 16
2.9.1. BGP CAR SAFI NLRI Format . . . . . . . . . . . . . . 16
2.9.2. Color-Aware Route NLRI Type . . . . . . . . . . . . . 17
2.9.3. IP Prefix NLRI Type . . . . . . . . . . . . . . . . . 23
2.9.4. Local-Color-Mapping (LCM) Extended-Community . . . . 24
2.10. LCM and BGP Color Extended-Community usage . . . . . . . 25
2.11. Error Handling . . . . . . . . . . . . . . . . . . . . . 26
3. Service Route Automated Steering on Color-Aware Path . . . . 27
4. Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.1. (E, C) Subscription and Filtering . . . . . . . . . . . . 28
5. Scaling . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.1. Ultra-Scale Reference Topology . . . . . . . . . . . . . 29
5.2. Deployment model . . . . . . . . . . . . . . . . . . . . 31
5.2.1. Flat . . . . . . . . . . . . . . . . . . . . . . . . 31
5.2.2. Hierarchical Design with Next-Hop-Self at Ingress
Domain BR . . . . . . . . . . . . . . . . . . . . . . 32
5.2.3. Hierarchical Design with Next-Hop-Unchanged at Ingress
Domain BR . . . . . . . . . . . . . . . . . . . . . . 34
5.3. Scale Analysis . . . . . . . . . . . . . . . . . . . . . 35
5.4. Scaling Benefits of the (E, C) BGP Subscription and
Filtering . . . . . . . . . . . . . . . . . . . . . . . . 37
5.5. Anycast SID . . . . . . . . . . . . . . . . . . . . . . . 37
5.5.1. Anycast SID for Transit Inter-domain Nodes . . . . . 38
5.5.2. Anycast SID for Transport Color Endpoints (e.g.,
PEs) . . . . . . . . . . . . . . . . . . . . . . . . 38
6. Routing Convergence . . . . . . . . . . . . . . . . . . . . . 38
7. CAR SRv6 . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 38
7.1.1. Routed Service SID . . . . . . . . . . . . . . . . . 39
7.1.2. Non-routed Service SID . . . . . . . . . . . . . . . 39
7.2. Deployment Options For CAR SRv6 Locator Reachability
Distribution and Forwarding . . . . . . . . . . . . . . . 41
7.2.1. Hop by Hop IPv6 Forwarding for BGP SRv6 Prefixes . . 41
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7.2.2. Encapsulation between BRs for BGP SRv6 Prefixes . . . 41
7.3. Operational Benefits of using CAR SAFI for SRv6 Locator
Prefix Distribution . . . . . . . . . . . . . . . . . . . 42
8. CAR IP Prefix Route . . . . . . . . . . . . . . . . . . . . . 43
9. VPN CAR . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
9.1. Format and Encoding . . . . . . . . . . . . . . . . . . . 45
9.1.1. VPN CAR Type-1 NLRI . . . . . . . . . . . . . . . . . 46
9.1.2. VPN CAR Type-2 (IP Prefix) NLRI . . . . . . . . . . . 46
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 47
10.1. BGP CAR NLRI Types Registry . . . . . . . . . . . . . . 47
10.2. BGP CAR NLRI TLV Registry . . . . . . . . . . . . . . . 48
10.3. Guidance for Designated Experts . . . . . . . . . . . . 48
10.4. BGP Extended-Community Registry . . . . . . . . . . . . 48
11. Manageability and Operational Considerations . . . . . . . . 49
12. Security Considerations . . . . . . . . . . . . . . . . . . . 49
13. Co-authors . . . . . . . . . . . . . . . . . . . . . . . . . 50
14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 51
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 52
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 52
16.1. Normative References . . . . . . . . . . . . . . . . . . 52
16.2. Informative References . . . . . . . . . . . . . . . . . 54
Appendix A. Illustrations of Service Steering . . . . . . . . . 56
A.1. E2E BGP transport CAR intent realized using IGP
Flex-Algo . . . . . . . . . . . . . . . . . . . . . . . . 56
A.2. E2E BGP transport CAR intent realized using SR Policy . . 57
A.3. BGP transport CAR intent realized in a section of the
network . . . . . . . . . . . . . . . . . . . . . . . . . 59
A.3.1. Provide intent for service flows only in core domain
running ISIS Flex-Algo . . . . . . . . . . . . . . . 59
A.3.2. Provide intent for service flows only in core domain
over TE tunnel mesh . . . . . . . . . . . . . . . . . 61
A.4. Transit network domains that do not support CAR . . . . . 63
A.5. Resource Avoidance using BGP CAR and IGP Flex-Algo . . . 64
A.6. Per-Flow Steering over CAR routes . . . . . . . . . . . . 66
A.7. Advertising BGP CAR routes for shared IP addresses . . . 67
Appendix B. Color Mapping Illustrations . . . . . . . . . . . . 69
B.1. Single color domain containing network domains with N:N
color distribution . . . . . . . . . . . . . . . . . . . 69
B.2. Single color domain containing network domains with N:M
color distribution . . . . . . . . . . . . . . . . . . . 69
B.3. Multiple color domains . . . . . . . . . . . . . . . . . 73
Appendix C. CAR SRv6 Illustrations . . . . . . . . . . . . . . . 74
C.1. BGP CAR SRv6 locator reachability hop by hop
distribution . . . . . . . . . . . . . . . . . . . . . . 74
C.2. BGP CAR SRv6 locator reachability distribution with
encapsulation . . . . . . . . . . . . . . . . . . . . . . 77
C.3. BGP CAR (E, C) route distribution . . . . . . . . . . . . 79
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Appendix D. CAR SAFI NLRI update packing efficiency
calculation . . . . . . . . . . . . . . . . . . . . . . . 82
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 86
1. Introduction
BGP Color-Aware Routing (CAR) is a 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 router, for different
intents or colors. Color is a 32-bit numerical value associated with
a network intent (low-cost, low-delay, avoid some resources etc.) as
defined in [RFC9256].
BGP CAR fulfills the transport and VPN problem statement and
requirements described in
[I-D.hr-spring-intentaware-routing-using-color].
For this purpose, this document specifies two new BGP SAFIs, called
BGP CAR SAFI (83) and VPN CAR SAFI (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 the provider network. The transport network may
comprise of multiple BGP ASes or multiple IGP domains within a single
BGP AS (e.g., [I-D.ietf-mpls-seamless-mpls]). BGP CAR SAFI can also
be enabled within a VRF on a PE router towards a peering 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 network, 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 both customer and
provider network domains.
The document also defines two BGP CAR route types for this purpose.
The BGP CAR Type-1 NLRI enables the generation and distribution of
multiple color-aware routes to the same destination IP prefix for
different colors. This case is applicable to situations where a
transport node such as a PE has a common IP address (such as a
loopback) to advertise for multiple intents. This address is used as
the BGP next hop for service routes and as the transport endpoint for
the data plane path. Multiple routes are needed for this same
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address or prefix to set up a unique path for each intent. One
example is setting up multiple MPLS/SR-MPLS LSPs to an egress PE, one
per intent.
The BGP CAR Type-2 NLRI 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 is 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.
BGP CAR adheres to the flat routing model of BGP-IP/LU(Labeled
Unicast) but extends it to support intent-awareness, thereby
providing a consistent operational experience with those widely
deployed transport routing technologies.
1.1. Terminology
+=============+===================================================+
+=============+===================================================+
| Intent (in | Any combination of the following behaviors: a) |
| routing) | Topology path selection (e.g. minimize metric or |
| | avoid resource), b) NFV service insertion (e.g. |
| | service chain steering), c) per-hop behavior |
| | (e.g. a 5G slice). This is a more specific |
| | concept w.r.t. routing beyond best-effort, |
| | compared to intent as declarative abstraction in |
| | [RFC9315]. |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
| Color | A 32-bit numerical value associated with an |
| | intent (e.g. low-cost , low-delay, or avoid some |
| | resources) as defined in [RFC9256] Section 2.1. |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
| Colored | An egress PE (e.g. E2) colors its BGP service |
| Service | (e.g. VPN) route (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 in the locator part of SRv6 |
| | Service SID [RFC9252]. |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
| Color-Aware | A path to forward packets towards E2 which |
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| Path to | satisfies the intent associated with color C. |
| (E2, C) | Several technologies may provide a Color-Aware |
| | Path to (E2, C): SR Policy [RFC9256], IGP Flex- |
| | Algo [RFC9350], BGP CAR [specified in this |
| | document]. |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
| Color-Aware | A distributed or signaled route that builds a |
| Route (E2, | color-aware path to E2 for color C. |
| C) | |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
| Service | An ingress PE (or ASBR) E1 automatically steers a |
| Route | C-colored service route V/v from E2 onto an (E2, |
| Automated | C) color-aware path. If several such paths |
| Steering on | exist, a preference scheme is used to select the |
| Color-Aware | best path (for example, IGP Flex-Algo preferred |
| Path | over SR Policy preferred over BGP CAR. |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
| Color | A set of nodes which share the same Color-to- |
| Domain | Intent mapping, typically under single |
| | administration. This set can be organized into |
| | one or multiple network domains (IGP 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]. |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
| Resolution | An inter-domain BGP CAR route (E, C) from 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 with the |
| vs Steering | terminology used in the SR Policy document |
| | [RFC9256] Section 8, (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 color-aware path. |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
| | Service Steering: Service route maps traffic to a |
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| | BGP CAR path (or other Color-Aware Path: e.g. SR |
| | Policy). If a Color-Aware Path is not available, |
| | local policy may map to traditional routing/TE |
| | path (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 and SRv6. |
+-------------+---------------------------------------------------+
+-------------+---------------------------------------------------+
| | Intra-Domain Resolution: BGP CAR route maps to |
| | intra-domain color aware path (e.g. SR Policy, |
| | IGP Flex-Algo, BGP CAR) or traditional routing/TE |
| | path (e.g. RSVP-TE, IGP/LDP, BGP-LU). |
+-------------+---------------------------------------------------+
Table 1
Abbreviations:
* BR: An inter-domain Border Router, either for an IGP Area (ABR) or
a BGP Autonomous System (ASBR).
* P node: An intra-domain transport router.
* RR: BGP Route Reflector.
* AFI/SAFI: BGP Address-Family/Sub-Address-Family.
* BGP-LU: BGP Labeled Unicast SAFI [RFC8277].
* BGP-IP: BGP IPv4/IPv6 Unicast AFI/SAFIs [RFC4271], [RFC4760].
* V/v, W/w: Generic representations of a service route (indicating
prefix/masklength), regardless of AFI/SAFI or actual NLRI
encoding.
* Color-EC: BGP Color Extended-Community.
* LCM-EC: BGP Local Color Mapping Extended-Community.
1.2. Illustration
Here is a brief illustration of the salient properties of the BGP CAR
solution.
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+-------------+ +-------------+ +-------------+
| | | | | | V/v with C1
|----+ |------| |------| +----|/
| E1 | | | | | | E2 |\
|----+ | | | | +----| W/w with C2
| |------| |------| |
| Domain 1 | | Domain 2 | | Domain 3 |
+-------------+ +-------------+ +-------------+
Figure 1
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" 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" and
hence C2
E1 receives two service routes from E2:
* V/v with BGP Color Extended-Community C1
* W/w with BGP Color Extended-Community C2
E1 has the following color-aware paths:
* (E2, C1) provided by BGP CAR with the following per-domain
support:
- Domain1: over IGP FA1
- Domain2: over SR Policy bound to color C1
- Domain3: over IGP FA1
* (E2, C2) provided by SR Policy
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 SR Policy
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Illustrated Properties:
* Leverage of the BGP Color Extended-Community
- The service routes are colored with widely used BGP Color
Extended-Community [RFC9012] to request intent
* (E, C) Automated Steering
- V/v and W/w are automatically steered on the appropriate color-
aware path
* Seamless co-existence 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 dataplane: with 300k PE's and 5 colors, the BGP CAR solution
ensures that no single node needs to support a dataplane scaling
in the order of Remote PE * C (Section 5). This would otherwise
exceed the MPLS dataplane.
* Control-Plane: a node should not install a (E, C) path if it's not
participating in that color-aware path.
* Incongruent Color-Intent mapping: the solution supports the
signaling of a BGP CAR route across different color domains
(Section 2.8)
The keys to this simplicity are:
* the leverage of the BGP Color Extended-Community [RFC9012] to
color service routes
* 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 definition of the data model of a BGP CAR path: (E, C)
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- natural extension of BGP IP/LU data model (E)
- consistent with SR Policy data model
* 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) which may itself be provided by BGP CAR or via another
color-aware routing solution: SR Policy, IGP 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: Falls into two categories, to accommodate the 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 or Color) distinguishes
the color-aware route. Color is not necessary in NLRI key as a
distinguisher.
* NLRI non-key encapsulation data: MPLS label stack, Label index,
SRv6 SID list etc.
* BGP Next Hop.
* AIGP Metric [RFC7311]: accumulates color/intent specific metric
value for a CAR route across multiple BGP hops.
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* Local-Color-Mapping Extended-Community (LCM-EC): Optional 32-bit
Color value used to represent the intent associated with the CAR
route:
- when a CAR route propagates between different color domains.
- when a CAR route has a unique IP prefix for an intent.
* BGP Color Extended-Community (Color-EC): Optional 32-bit Color
value used to represent the intent associated with the CAR BGP
next hop, as per [RFC9256].
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 ensured by:
* NLRI Route-Type field: provides extensibility to add new NLRI
formats for new route-types.
* Key length: field enables handling of unsupported route-types
opaquely, enabling transitivity via RRs.
* TLV-based encoding of non-key part of NLRI: enables flexible
support for multiple encapsulations with efficient update packing.
* AIGP Attribute 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., SR Policy, IGP Flex-Algo, RSVP-TE, BGP-LU
[RFC8277].
2.4. BGP CAR Route Validation
A BGP CAR path (E, C) from N with encapsulation T is valid if color-
aware path (N, C) exists with encapsulation T available in dataplane.
A local policy may customize the validation process:
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* the color constraint in the first check may be relaxed: instead N
is reachable via alternate color(s) or in the default routing
table.
* the dataplane 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. 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 mechanisms such as IGP
Flex-Algo, SR policy 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) from N may be resolved over a
color-aware route (N, C2): i.e. the local policy maps the
resolution of C1 over a different color 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 via C2
* The resolution of (N, C1) may be egress driven. In an SRv6
domain, node N selects and advertises an SRv6 SID from a locator
for intent C1, with a BGP CAR route. In such a case, the ingress
node resolves the SRv6 SID over a route for the intent aware
locator of N or its summary provided by SRv6 Flex Algo or BGP CAR
Type-2 route itself (e.g., Appendix C.2).
* Resolution may be mapped 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).
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Route resolution via a different color C2 can be automated by
attaching BGP Color Extended-Community C2 to CAR route (E2, C1),
leveraging Automated steering as described in Section 8.4 of Segment
Routing Policy Architecture [RFC9256] for BGP CAR routes. This
mechanism is illustrated in section B.2. This mechanism SHOULD be
supported.
For a CAR route, Color-EC color takes precedence over the route's
effective intent color (LCM-EC if present (Section 2.9.4), or else
NLRI color).
Local policy takes precedence over the 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 Type-1 route resolves over CAR Type-2.
CAR Type-2 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 carrying
Tunnel Encapsulation attribute (TEA). In this case, procedures of
section 8 of [RFC9012] apply to BGP CAR routes, using color
precedence as specified above for resolution. Among other options, a
BGP CAR BR may advertise a BGP CAR route to an ingress BR with a
specific BGP next hop per color, with a TEA or Tunnel Encapsulation
EC, as per Section 6 of [RFC9012].
2.6. AIGP Metric Computation
The Accumulated IGP (AIGP) 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.
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If BGP CAR routes traverse across a discontinuity in the transport
path for a given intent, a penalty is added in accumulated IGP metric
(value set by user policy). For instance, when color C1 path is not
available, and route resolves via color C2 path (e.g., Appendix A.3).
AIGP metric computation is recursive.
To avoid continuous IGP metric changes causing end to end BGP CAR
route churn, an implementation should provide thresholds to trigger
AIGP update.
Additional AIGP extensions may be defined to signal state for
specific use-cases: MSD along the BGP CAR route advertisement,
Minimum MTU along the BGP CAR advertisement. This is out of scope
for this document.
2.7. Native 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 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 2 and domain 1. Let us assume
that these two domains do not share the same color-to-intent mapping.
Low-delay in domain 2 is color C2, while it is C1 in domain 1 (C1 <>
C2).
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 illustrated below:
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* Within 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 (as per classic peering agreement) of the intent-to-
color mapping within domain 2 ("low-delay" in domain 2 is C2).
* A maps C2 in LCM-EC to C1 and signals within domain 1 the received
BGP CAR route as (E2, C2) via A with LCM-EC(C1).
* The nodes within the receiving 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/or receiving
peer:
* Control which routes are advertised to or accepted from a peer in
a different color domain.
* Attach LCM-EC if not present, or if present update the value to
re-map the color as needed. This may be done by the advertising
speaker or the receiving speaker as determined by the operator
peering agreement.
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.
Salient properties:
* The NLRI never changes, even though the color-to-intent mapping
changes
* E is globally unique, which makes E-C in that order unique
* In the vast majority of the cases, the color of the NLRI is used
for resolution and steering
* In the rare case of color incongruence, the local color encoded in
LCM-EC takes precedence
Operational consideratons are in Section 11. Further illustrations
are provided in Appendix B.
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2.9. Format and Encoding
BGP CAR leverages the BGP multi-protocol extensions [RFC4760] and
uses the MP_REACH_NLRI and MP_UNREACH_NLRI attributes for route
updates by using the SAFI value 83 along with AFI 1 for IPv4 prefixes
and AFI 2 for IPv6 prefixes.
BGP speakers MUST use 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 3 of [RFC2545]. Processing of the Next Hop field is governed
by standard BGP procedures as described in section 3 of [RFC4760].
The sub-sections below specify the generic encoding of the BGP CAR
NLRI 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 Key Fields //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type-specific Non-Key Fields (if applicable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* NLRI Length: 1 octet field that indicates the length in octets of
the NLRI excluding the NLRI Length field itself.
* Key Length: 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 field that indicates the type of the BGP CAR
NLRI.
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* Type-Specific Key Fields: Depend on the NLRI type and of length
indicated by the Key Length.
* Type-Specific Non-Key Fields: optional and variable depending on
the NLRI type. The NLRI definition allows for encoding of
specific non-key information associated with the route (i.e. the
key) as part of the NLRI for efficient packing of BGP updates.
The indication of the key length enables BGP Speakers to determine
the key portion of the NLRI and use it along with the NLRI Type field
in an opaque manner for 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.
It also helps make error handling more resilient and minimally
disruptive as described in Section 2.11.
A route (NLRI) can carry more than one non-key TLV (of different
types). This provides significant benefits such as signaling
multiple encapsulations simultaneously for the same route, each with
a different value (label/SID etc). This enables simpler, efficient
migrations with low overhead :
* avoids need for duplicate routes to signal different
encapsulations
* avoids need for separate control planes for distribution
* preserves update packing (e.g. Appendix D)
The non-key portion of the NLRI MUST be omitted while carrying it
within the MP_UNREACH_NLRI when withdrawing the route advertisement.
2.9.2. Color-Aware Route NLRI Type
The Color-Aware Routes NLRI Type is used for advertisement of color-
aware routes and has the following format:
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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 by optional TLVs encoded as below:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Value (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* NLRI Length: variable
* Key Length: 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
maximum length is 9. For IPv6 (AFI=2), the minimum length is 5
and maximum length is 21.
* NLRI Type: 1
* Type-Specific Key Fields: as below
- Prefix Length: 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
size field that contains the most significant octets of the
prefix, i.e., 0 octet for prefix length 0, 1 octet for prefix
length 1 to 8, 2 octets for prefix length 9 to 16, 3 octets for
prefix length 17 up to 24, 4 octets for prefix length 25 up to
32, and so on. 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 is irrelevant. 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 color value associated with the
prefix.
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* Type-Specific Non-Key Fields: specified in the form of optional
TLVs as below:
- 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:
o R: Bit is reserved and MUST be set to 0 and ignored on
receive.
o T: Transitive bit, applicable to speakers that change the
BGP CAR next hop
+ T bit set to indicate TLV is transitive. An unrecognized
transitive TLV MUST be propagated by a speaker that
changes the next hop
+ T bit unset to indicate TLV is non-transitive. An
unrecognized non-transitive TLV MUST NOT be propagated by
a speaker that changes next hop
A speaker that does not change next hop SHOULD propagate all
received TLVs.
o Type code: Remaining 6 bits contain the type of the TLV.
- Length: 1 octet field that contains the length of the value
portion of the non-key TLV in terms of octets
- Value: variable length field as indicated by the length field
and to be interpreted as per the type field.
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.
The Color is introduced to enable multiple route advertisements for
the same prefix. The color is associated with an intent (e.g. low-
latency) in originator color-domain.
The following sub-sections specify the non-key TLVs associated with
the Color-Aware Routes NLRI type.
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2.9.2.1. Label TLV
The Label TLV is used for advertisement of color-aware routes along
with their MPLS labels and 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|T| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Followed by one (or more) Labels encoded as below:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label |Rsrv |S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type : Type code is 1. T bit MUST be unset
* Length: variable, MUST be a multiple of 3
* Label Information: multiples of 3 octet fields to convey the MPLS
label(s) associated with the advertised color-aware route. It is
used for encoding a single label or a stack of labels for usage as
described in [RFC8277]. Number of labels is derived from length
field. 3-bit Rsrv and 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 specific
prefix and color combination, 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 advertisement of Segment Routing MPLS
(SR-MPLS) Segment Identifier (SID) [RFC8402] information associated
with the labeled color-aware routes and has the following format:
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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 code is 2. T bit MUST be set
* Length: 7
* Reserved: 1 octet field that MUST be set to 0 and ignored on
receipt.
* Flags: 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).
* Label Index: 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).
This TLV provides the equivalent functionality as Label Index TLV of
[RFC8669] for Transport CAR route in SR-MPLS deployments. It
provides much better packing efficiency by carrying Label Index in
NLRI instead of in the BGP Prefix-SID Attribute (Appendix D).
Label Index TLV MUST not be carried in the Prefix-SID attribute for
BGP CAR routes. If a speaker receives a CAR route with Label Index
TLV in the Prefix-SID attribute, it SHOULD ignore it. The BGP
Prefix-SID Attribute SHOULD NOT be sent with the labeled color-aware
routes if the attribute is being used only to convey the Label Index
TLV.
If a BGP transport CAR speaker sets itself as the next hop while
propagating a CAR route, it allocates a local label for the specific
prefix and color combination. When the received BGP update has the
CAR Label Index TLV, the speaker SHOULD use that hint to allocate the
local label from the SR Global Block (SRGB) using procedures as
specified in [RFC8669] Section 4.
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2.9.2.3. SRv6 SID TLV
BGP Transport CAR can be also used to setup end-to-end color-aware
connectivity using Segment Routing over IPv6 (SRv6) [RFC8402].
[RFC8986] specifies the SRv6 Endpoint behaviors (e.g. End PSP) which
MAY be leveraged for BGP CAR with SRv6. The SRv6 SID TLV is used for
advertisement of color-aware routes along with their SRv6 SIDs and
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|T| Type | Length | SRv6 SID Info (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type : Type code is 3. T bit MUST be unset
* Length: variable, MUST be either less than or equal to 16, or be a
multiple of 16
* SRv6 SID Information: field of size as indicated by the length
that either carries the SRv6 SID(s) for the advertised color-aware
route as one of the following:
- A single 128-bit SRv6 SID or a stack of 128-bit SRv6 SIDs
- A transposed portion (refer [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 encoding of SIDs avoids robustness issue caused by
overloading of MPLS label fields.
* Simple encoding to signal Unique SIDs (non-transposition),
maintaining BGP update prefix packing
* Highly efficient transposition scheme (12-14 bytes saved per
NLRI), also maintaining BGP update prefix packing
The BGP color-aware 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], transposed part of SID is carried in SRv6 SID
TLV and not limited by MPLS label field size.
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[I-D.agrawal-spring-srv6-mpls-interworking] describes MPLS and SRv6
interworking procedures and extension to BGP CAR routes.
2.9.3. 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Prefix (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Followed by optional TLVs encoded as below:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|T| Type | Length | Value (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* NLRI Length: variable
* Key Length: 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 maximum length is 5.
For IPv6 (AFI=2), the minimum length is 1 and maximum length is
17.
* NLRI Type: 2
* Type-Specific Key Fields: as below
- Prefix Length: 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
size field that contains the most significant octets of the
prefix, i.e., 0 octet for prefix length 0, 1 octet for prefix
length 1 to 8, 2 octets for prefix length 9 to 16, 3 octets for
prefix length 17 up to 24, 4 octets for prefix length 25 up to
32, and so on. 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 is irrelevant. 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).
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* Type-Specific Non-Key Fields: Encoded as per Type-Specific Non-Key
Fields of Color-Aware Routes NLRI Type in Section 2.9.2.
2.9.4. 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 reserved field that MUST be set to zero on
transmission and ignored on reception.
* Color: 4-octet field that carries the 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. low latency) in other
(transit or destination) color domains.
For Type-2 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 two BGP paths for a route have different LCM values, it is
considered an error and the route is not considered for bestpath
selection.
If present, LCM-EC is the effective intent of a BGP CAR route.
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LCM-EC Color is used instead of the Color in CAR route NLRI for
procedures described in earlier sections such as route validation,
resolution, AIGP calculation and steering.
The LCM-EC MAY be used for filtering of BGP CAR routes and/or for
applying routing policies for the intent, when present.
2.10. LCM and BGP Color Extended-Community usage
There are 2 distinct requirements to be supported as stated in
[I-D.hr-spring-intentaware-routing-using-color]":
1. Domains with different intent granularity (section 6.3.1.9)
2. Network domains under different administration, i.e. color
domains (section 6.3.1.10)
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. Example: 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, 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 described in
Section 2.5 and Appendix B.2, BGP Color Extended-Community is used to
automate the CAR route resolution.
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 as already described in Section 2.8 and
Appendix B.3.
Both LCM-EC and BGP Color Extended-Community may be present at the
same time with a BGP CAR route. Example: 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
(Appendix B.2 and Appendix B.3 combined).
As described in Section 2.5, default order of processing for
resolution in presence of LCM-EC is local policy, then BGP Color-EC
color, and finally LCM-EC color.
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2.11. Error Handling
The error handling actions as described in [RFC7606] are applicable
for handling of BGP update messages for BGP-CAR. 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'. 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.
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 number of
actual bytes encoded in NLRI and key fields respectively, regardless
of content being encoded.
Given NLRI length and Key length MUST be valid, failures in following
checks result in 'AFI/SAFI disable' or 'session reset':
* Minimum NLRI length (must be atleast 2, as key length and NLRI
type are required fields).
* Key Length MUST be at least two less than NLRI Length.
NLRI Type specific error handling:
* By default, a speaker SHOULD discard unrecognized or unsupported
NLRI type and move to next NLRI.
* Key length and key errors of known NLRI type SHOULD result in
discard of NLRI similar to unrecognized NLRI type.(This MUST be
logged for trouble shooting).
Transparent propagation of unrecognized NLRI type:
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* Key length allows unrecognized route types to transit through RR
transparently without a software upgrade. Such RR does not need
to interpret key portion of NLRI and works on opaque key of given
length. An implementation SHOULD provide a knob that controls the
RR unrecognized route type propagation behavior and possibly at
granularity of route type values allowed. This gives ability to
operator to allow specific route type transparent reflection based
on client speaker support.
* In such a case RR may reflect NLRIs with NLRI type specific key
length and field errors. Clients of such RR that consume the
route for installation will perform the key error handling of
known NLRI type or discard unrecognized type. This prevents
propagation of routes with NLRI errors any further in network.
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 and the 'treat-as-withdraw' approach MUST be
used.
* Type specific length constraints should be verified. The TLV MUST
be discarded if there is an error.
* If multiple instances of same type are encountered, all but the
first instance MUST be ignored.
* If a speaker that performs encapsulation to the BGP next hop does
not receive at least one recognized forwarding information TLV
with T bit unset (such as label or SRv6 SID), such NLRI is
considered invalid and not eligible for best path selection.
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
An ingress PE (or ASBR) E1 automatically steers a C-colored service
route V/v from E2 onto an (E2, C) color-aware path. If several such
paths exist, a preference scheme is used to select the best path:
E.g. IGP Flex-Algo first then SR Policy then BGP CAR.
An egress PE may request intent through the transport for service
routes using the BGP Color Extended-Community [RFC9012]. An ingress
PE steers service traffic over a CAR Type-1 route using the service
route's next hop and BGP Color Extended-Community.
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This is consistent with the automated service route steering on SR
Policy (a routing solution providing color-aware path) defined in
[RFC9256]. All the steering variations described in [RFC9256] are
applicable to BGP CAR color-aware path: on-demand steering, per-
destination, per-flow, CO-only. For brevity, please refer to
[RFC9256] Section 8.
Appendix A provides illustrations of service route automated steering
over BGP CAR Type-1 routes.
An egress PE may request intent through the transport for service
routes 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 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, EVPN
(SAFI 70), FlowSpec, and BGP-LU (SAFI 4).
4. Filtering
PE and BRs may support filtering of CAR routes, for instance to only
accept routes of locally configured colors.
RTC [RFC4684] may also be applied to the CAR SAFI, where Route Target
ECs [RFC4360] can be used to constrain distribution of CAR routes.
RT assignment may be via user policy, for example an RT value can be
assigned to all routes of a specific color.
4.1. (E, C) Subscription and Filtering
This section illustrate an (E, C) BGP subscription model that allows
to filter the (E, C) routes learned by a BGP CAR node.
E1-----------------A-------------------B-------------------E2
<--- (E2, C1) ----
-- F (E2, C1) --> --- F (E2, C1) -->
| |
<-- (E2, C1) ---- <--- (E2, C1) ----
* BGP CAR route (E2, C1) advertised by E2 is not unconditionally
distributed beyond a certain point (e.g., B)
* E1 subscribes to (E2, C1) by advertising a filter route F (E2, C1)
to its upstream peer A
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* If A has (E2, C1) in its BGP RIB, it will advertise (E2, C1) to E1
* If A does not have (E2, C1), it will advertise F (E2, C1) to its
peer B
* B will advertise (E2, C1) to A, which will distribute it to E1
E1 may trigger a subscription for BGP CAR route (E2, C1) as a result
of receiving a C1-colored service route V/v from E2, for on-demand
steering via (E2, C1).
On-demand subscription and filtering procedures are outside the scope
of this document.
5. Scaling
This section analyses the key scale requirement of
[I-D.hr-spring-intentaware-routing-using-color], specifically:
* No intermediate node dataplane 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 service route to E
While the requirements and design principles generally apply to any
transport, the analysis in this section focusses on MPLS / SR-MPLS
transport since the scaling constraints are specifically relevant to
these technologies. BGP CAR SAFI is used here, however the
considerations apply to any BGP SAFI that's used with MPLS/SR-MPLS,
such as [RFC8277] or [RFC8669].
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 provides an ultra-scale reference topology. Section 5.2
presents three design models to deploy BGP CAR in the reference
topology, including hierarchical options. Section 5.3 analyses the
scaling properties of each model. Section 5.4 illustrates the
scaling benefits of the (E, C) BGP subscription and filtering.
5.1. Ultra-Scale Reference Topology
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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 applies to the reference topology above:
* Independent ISIS/OSPF SR instance in each domain.
* Each domain has Flex Algo 128. Prefix SID for a node is 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 clients.
* Egress PE E2 advertises a VPN route RD:V/v with BGP Color extended
community 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.
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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
1. Node 451 advertises BGP CAR route (E2, C1) to 341, from which it
goes to 231 then to 121 and finally to E1.
2. Each BGP hop allocates local label and programs swap entry in
forwarding for (E2, C1).
3. E1 receives BGP CAR route (E2, C1) via 121 with label 168002.
1. Let's assume E1 selects that path.
4. E1 resolves BGP CAR route (E2, C1) via 121 on color-aware path
(121, C1).
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1. Color-aware path (121, C1) is FA128 path to 121 (label
168121).
5. E1's imposition color-aware label-stack for V/v is thus
1. 30030 <=> V/v
2. 168002 <=> (E2, C1)
3. 168121 <=> (121, C1)
6. 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: Heirarchical BGP transport CAR, Next-Hop-Self (NHS) at iBR
1. Node 451 advertises BGP CAR route (451, C1) to 341, from which
it goes to 231 and finally to 121.
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2. Each BGP hop allocates local label and programs swap entry in
forwarding for (451, C1).
3. 121 resolves received BGP CAR route (451, C1) via 231 (label
168451) on color-aware path (231, C1).
1. Color-aware path (231, C1) is FA128 path to 231 (label
168231).
4. 451 advertises BGP CAR route (E2, C1) via 451 to Transport RR
T-RR2, which reflects it to T-RR1, which reflects it to 121.
5. 121 receives BGP CAR route (E2, C1) via 451 with label 168002.
1. Let's assume 121 selects that path.
6. 121 resolves BGP CAR route (E2, C1) via 451 on color-aware path
(451, C1).
1. Color-aware path (451, C1) is BGP CAR path to 451 (label
168451).
7. 121 imposition of color-aware label stack for (E2, C1) is thus
1. 168002 <=> (E2, C1)
2. 168451 <=> (451, C1)
3. 168231 <=> (231, C1)
8. 121 advertises (E2, C1) to E1 with next hop self (121) and label
168002
9. E1 constructs same imposition color-aware label-stack for V/v
via (E2, C1) as in the flat model:
1. 30030 <=> V/v
2. 168002 <=> (E2, C1)
3. 168121 <=> (121, C1)
10. 121 performs swap operation on 168002 with hierarchical color-
aware label stack for (E2, C1) via 451 from step 7.
11. Nodes 231 and 341 perform swap operation on 168451 bound to
color-aware path (451, C1).
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12. 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: Heirarchical BGP transport CAR, Next-Hop-Unchanged
(NHU) at iBR
1. Nodes 341, 231 and 121 receive and resolve BGP CAR route (451,
C1) the same as in the previous model.
2. Node 121 allocates local label and programs swap entry in
forwarding for (451, C1).
3. 451 advertises BGP CAR route (E2, C1) to Transport RR T-RR2,
which reflects it to T-RR1, which reflects it to 121.
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4. Node 121 advertises (E2, C1) to E1 with next hop as 451 i.e.
next-hop-unchanged.
5. 121 also advertises (451, C1) to E1 with next hop self (121) and
label 168451.
6. E1 resolves BGP CAR route (451, C1) via 121 on color-aware path
(121, C1).
1. Color-aware path (121, C1) is FA128 path to 121 (label
168121).
7. E1 receives BGP CAR route (E2, C1) via 451 with label 168002.
1. Let's assume E1 selects that path.
8. E1 resolves BGP CAR route (E2, C1) via 451 on color-aware path
(451, C1).
1. Color-aware path (451, C1) is BGP CAR path to 451 (label
168451).
9. E1's imposition color-aware label-stack for V/v is thus
1. 30030 <=> V/v
2. 168002 <=> (E2, C1)
3. 168451 <=> (451, C1)
4. 168121 <=> (121, C1)
10. Nodes 121, 231 and 341 perform swap operation on 168451 bound to
(451, C1).
11. 451 performs swap operation on 168002 bound to color-aware path
(E2, C1).
5.3. Scale Analysis
The following two tables summarize the control-plane and dataplane
scale of these three models:
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| E1 | 121 | 231
-----+---------------------+---------------------+--------------------
FLAT | (E2,C) via (121,C) | (E2,C) via (231,C) | (E2,C) via (341,C)
-----+---------------------+---------------------+--------------------
H.NHS| (E2,C) via (121,C) | (E2,C) via (451,C) |
| | (451,C) via (231,C) | (451,C) via (341,C)
-----+---------------------+---------------------+--------------------
H.NHU| (E2,C) via (451,C) | |
| (451,C) via (121,C) | (451,C) via (231,C) | (451,C) via (341,C)
-----+---------------------+---------------------+--------------------
| E1 | 121 | 231
-----+---------------------+---------------------+--------------------
FLAT | V -> 30030 | 168002 -> 168002 | 168002 -> 168002
| 168002 | 168231 | 168341
| 168121 | |
-----+---------------------+---------------------+--------------------
H.NHS| V -> 30030 | 168002 -> 168002 | 168451 -> 168451
| 168002 | 168451 | 168341
| 168121 | 168231 |
-----+---------------------+---------------------+--------------------
H.NHU| V -> 30030 | 168451 -> 168451 | 168451 -> 168451
| 168002 | 168231 | 168341
| 168451 | |
| 168121 | |
-----+---------------------+---------------------+--------------------
* 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. 341), whose FIB capacity and even MPLS label space may
be exceeded.
- 341's dataplane scales with (E2,C) where there may be 300k E's
and 5 C's hence 1.5M entries > 1M MPLS dataplane.
* The hierarchical models avoid the need for core BRs to learn
routes and install label forwarding entries for (E, C) routes.
- Whether next-hop self or unchanged at 121, 341's dataplane
scales with (451,C) where there may be thousands of 451's and 5
C's hence well under the 1M MPLS dataplane.
- 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.
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* The next-hop-self option at ingress BRM (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 dataplane 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. 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. 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 dataplane option for the ingress PE.
5.4. Scaling Benefits of the (E, C) BGP Subscription and Filtering
The (E, C) subscription scheme from Section 4.1 provides the
following scaling benefits for the models in Section 5.2
* An ingress PE (E1) only learns (E, C) routes that it needs to
install into data plane for service route automated steering.
* An ingress BRM (121) only learns (E, C) routes that it needs to
install into data plane (for Next-Hop-Self), or that it needs to
distribute towards it's ingress PEs (inline RR with Next-Hop-
Unchanged).
* An ingress BRM or a transport RR only needs to distribute the
necessary subset of (E, C) routes to each client (subscriber);
this minimizes their processing load for generating updates.
* As a result, withdrawal of (E, C) routes when a remote node fails
(E2), may also be faster, aiding better convergence.
5.5. Anycast SID
This section describes how Anycast SID complements and improves the
scaling designs above.
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5.5.1. Anycast SID for Transit Inter-domain Nodes
* Redundant BRs (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.
5.5.2. 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' paired with E2 above. 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. But its applicability is limited to cases
where the constraints above 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 5.5 can provide further
convergence optimizations for BR and PE failures deployed in
redundant designs.
7. CAR SRv6
7.1. Overview
Two distinct cases apply to steering services over SRv6 based intent-
aware multi-domain transport paths, as described in Section 5 of
[RFC9252].
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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
([RFC9252]).
The intent-aware transport path to the locator of the egress PE is
provided by underlay IP routing, such as IGP Flex-Algo [RFC9350]
within a domain, and BGP-CAR across multiple IGP domains or BGP ASNs.
An SRv6 locator is assigned for a given intent or color. This
locator prefix is distributed using BGP-CAR to ingress PEs in a
remote domain. 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 for this purpose described
in Section 2.9.3 and Section 8.
The SRv6 locator may be shared with an IGP Flex-Algo, or may be
assigned specific to BGP CAR for a given intent. A BGP CAR
advertised SRv6 locator prefix may also be used for resolution of the
SRv6 service SID advertised for best effort connectivity.
Appendix C.1 and Appendix C.2 illustrates the control and forwarding
behaviors for routed SRv6 Service SID.
Section 7.2 describes the deployment options.
Section 7.3 describes operational considerations of using BGP CAR
SAFI vs BGP IPv6 SAFI for inter-domain route distribution of SRv6
locators.
7.1.2. Non-routed Service SID
The SRv6 Service SID allocated by an egress PE is not routed. The
service route is advertised by the egress PE with a Color Extended-
Community C ([RFC9252] section 5).
The intent-aware path within an egress domain is provided by an SR-TE
or similar policy to the egress PE (E, C) [RFC9256]. This (E, C)
policy is distributed into the multi-domain network from egress BRs
using a BGP-CAR Type-1 route, towards ingress PEs in other domains.
This signaling is the same as for SR-MPLS, as described in earlier
sections.
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The (E, C) BGP CAR Type-1 route is advertised from a BR with an SRv6
transport SID allocated from a 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.
An ingress PE in a remote domain steers a received service route with
Color C via this (E, C) BGP CAR route, as described in Section 3.
Additionally, the ingress PE resolves the SRv6 transport SID received
in the (E, C) CAR route via another underlay intent-aware route.
BGP-CAR may also provide the underlay intent-aware inter-domain
reachability to this SRv6 transport SID:
* An egress domain BR advertises an IP Prefix Type-2 CAR route for
the locator prefix that covers the SRv6 transport SID allocated by
the egress BR for this (E, C) route. This IP Prefix CAR route is
distributed across BGP hops in the underlay towards ingress PEs
similar to previous case and may be summarized.
* Thus, the colored service route resolves via the Type-1 CAR route,
which in turn carries a SRv6 transport SID that resolves via the
Type-2 CAR route. Multiple Type-1 routes may resolve via a single
Type-2 route.
Note: This is the typical resolution order as the Type-2 route
provides intent-aware reachability to the BRs that advertise the
Type-1 specific routes for each egress PE. However, there can be
use-cases where a Type-2 route may resolve via a Type-1 route.
An 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.
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).
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7.2. Deployment Options 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, such as an
ABR or ASBR for forwarding. A few options to forward packets for BGP
SRv6 prefixes described in
([I-D.agrawal-spring-srv6-mpls-interworking] also apply to BGP CAR as
follows:
7.2.1. Hop by Hop IPv6 Forwarding for BGP SRv6 Prefixes
* Hop by hop IPv6 lookup and forwarding on both BRs and P nodes in a
domain.
- No tunnel encapsulation between BRs in a domain.
- No per-PE SID allocation and installation on any BGP hop.
* P nodes need to learn BGP SRv6 routes. With summarization, route
scale requirements can be minimized.
* BGP routing is enabled on all internal nodes (iBGP).
* BRs distribute external SRv6 routes to internal peers.
- Next-hop unchanged with recursive resolution via IGP at each
hop.
* Similar to Internet / BGP IP routing well-known model.
- Can support large scale route distribution.
Illustration in Appendix C.1.
7.2.2. Encapsulation between BRs for BGP SRv6 Prefixes
* IPv6 lookup and forwarding for BGP SRv6 prefixes only on BGP BRs.
- P nodes do not learn or install these prefixes.
* SRv6 (or other) encapsulation to reach the BGP SRv6 next hop.
- Not needed for connected next hops, such as eBGP single-hop.
* SRv6 outer encapsulation may be H.Encaps.Red or H.Insert.Red.
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* BGP route distribution between BRs (via RRs, or directly if
single-hop eBGP).
* An egress BR sets itself as BGP next hop, selects and advertises
an appropriate SID for SRv6 based encapsulation towards itself.
- BGP next hop and SID for specific intent within domain.
* An ingress BR encapsulates SRv6 egress PE destined packets with
encapsulation to BGP next hop, ie. Egress BR.
* If SRv6 encapsulation, then SID from egress BR is common SID,
shared by multiple BGP SRv6 prefixes.
- No per-PE SID allocation and installation on any BGP hop.
* If MPLS/SR-MPLS transport, route will carry label/prefix-SID
allocated by next hop, may be shared.
Illustration in Appendix C.2.
7.3. Operational Benefits of 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.agrawal-spring-srv6-mpls-interworking]
(Section 7.1.2) or [I-D.wang-idr-cpr].
Using the BGP CAR SAFI provides significant operational advantages:
* 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 inadvertent leaking of routes.
o Avoiding need to configure specific route filters for
locator routes.
- Priority handling of infrastructure prefixes over Internet
prefixes.
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* 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.
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 RFC 4271 and RFC 2545
semantics. Type-2 routes are installed in the default routing and
forwarding table and provide longest-prefix-match forwarding. This
is unlike Type-1 routes, where it is the signaled forwarding data
such as labels/SIDs that are installed in the forwarding table to
create end to end paths.
Type-2 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:
* SRv6 locator prefix with color for specific intents.
* SRv6 locator prefix without color for best effort.
* Best effort transport reachability to a PE/BR without color.
For specific intents, color may be signaled with the CAR Type-2 route
for purposes such as intent-aware SRv6 SID or BGP next-hop selection
at each transit BR, color based routing policies and filtering, and
intent-aware next-hop resolution (Section 2.5), same as with Type-1
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.
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A special case of intent is best effort which may be represented by a
color and follow above procedures. But to be compatible with
traditional operational usage, CAR Type-2 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 (RFC 4271) and BGP-LU (RFC 8277). However, if
such routes are also distributed in these SAFIs, a router may receive
both BGP CAR SAFI paths and IP/LU SAFI paths. By default, CAR SAFI
transport path is preferred over BGP IP or BGP-LU SAFI path.
A BGP transport CAR speaker that supports packet forwarding lookup
based on 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 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], using MPLS transport
as an example.
CE1 -------------- PE1 -------------------- PE2 -------------- CE2 - V
* BGP CAR SAFI is enabled on CE1-PE1 and PE2-CE2 sessions
* BGP VPN CAR SAFI is enabled between PE1 and PE2
* Provider publishes intent 'low-delay' is mapped to color CP on its
inbound peering links
* Within its infrastructure, Provider maps intent 'low-delay' to
color CPT
* On CE1 and CE2, intent 'low-delay' is mapped to CC
(V, CC) is a Color-Aware route originated by CE2
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1. CE2 sends to PE2 : [(V, CC), Label L1] via CE2 with LCM (CP)
2. PE2 installs in VRF A: [(V, CC), L1] via CE2
which resolves on (CE2, CP)
or connected OIF
2.a. PE2 allocates VPN Label L2 and programs swap entry for (V, CC)
3. PE2 sends to PE1 : [(RD, V, CC), L2] via PE2
with regular Color Extended
Community (CPT)
4. PE1 installs in VRF A: [(V, CC), L2] via (PE2, CPT)
steered on (PE2, CPT)
4.a. PE1 allocates Label L3 and programs swap entry for (V, CC)
5. PE1 sends to CE1 : [(V, CC), L3] via PE1
without any LCM
6. CE1 installs : [(V, CC), L3] via PE1
which resolves on (PE1, CC)
or connected OIF
6.a. Label L3 is installed as the imposition label for (V, CC)
VPN CAR distribution for (RD, V, CC) requires a new SAFI that follows
same VPN semantics as defined in [RFC4364], the difference being that
the advertised routes carry CAR NLRI defined in Section 2.9.2 and
Section 2.9.3 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 steering as described in
Section 3 and illustrated in example above.
CAR routes distributed in VPN CAR SAFI are infrastructure routes
advertised by CEs in different customer VRFs on a PE. Example use-
cases are intent-aware L3VPN CsC ([RFC4364] Section 9) and SRv6 over
a provider 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 the BGP multi-protocol extensions
[RFC4760] and uses the MP_REACH_NLRI and MP_UNREACH_NLRI attributes
for route updates by using the SAFI value 84 along with AFI 1 for
IPv4 VPN CAR prefixes and AFI 2 for IPv6 VPN CAR prefixes.
BGP speakers MUST use 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.
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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 3.2.1.1 of [RFC4659].
9.1.1. VPN CAR Type-1 NLRI
VPN CAR Type-1 NLRI with RD has the format 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 |Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Distinguisher |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Distinguisher |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Prefix (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Followed by optional TLVs encoded as below:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|T| Type | Length | Value (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* All fields are encoded as per Section 2.9.2.
* Key Length: It indicates the total length comprised of the RD,
Prefix Length field, IP Prefix field, and the Color field
* Route Distinguisher: 8 octet field encoded according to [RFC4364]
9.1.2. VPN CAR Type-2 (IP Prefix) NLRI
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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 by optional TLVs encoded as below:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|T| Type | Length | Value (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* All fields are encoded as per Section 2.9.3.
* Key Length: It indicates the total length comprised of the RD,
Prefix Length field and IP Prefix field
* Route Distinguisher: 8 octet field encoded according to [RFC4364]
10. IANA Considerations
IANA has assigned SAFI value 83 (BGP CAR) and SAFI value 84 (BGP VPN
CAR) from the "SAFI Values" sub-registry under the "Subsequent
Address Family Identifiers (SAFI) Parameters" registry with this
document as a reference.
10.1. BGP CAR NLRI Types Registry
IANA is requested to create a "BGP CAR NLRI Types" sub-registry under
the "Border Gateway Protocol (BGP) Parameters" registry with this
document as a reference. The registry is for assignment of the one
octet sized code-points for BGP CAR NLRI types and populated with the
values shown below:
Type NLRI Type Reference
-----------------------------------------------------------------
0 Reserved (not to be used) [This document]
1 Color-Aware Route NLRI [This document]
2 IP Prefix NLRI [This document]
3-255 Unassigned
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Allocations within the registry are to be made under the
"Specification Required" policy as specified in [RFC8126]).
10.2. BGP CAR NLRI TLV Registry
IANA is requested to create a "BGP CAR NLRI TLV Types" sub-registry
under the "Border Gateway Protocol (BGP) Parameters" registry with
this document as a reference. The registry is for assignment of the
one octet sized code-points for BGP-CAR NLRI non-key TLV types and
populated with the values shown below:
Type NLRI Type Reference
-----------------------------------------------------------------
0 Reserved (not to be used) [This document]
1 Label TLV [This document]
2 Label Index TLV [This document]
3 SRv6 SID TLV [This document]
4-64 Unassigned
Allocations within the registry are to be made under the
"Specification Required" policy as specified in [RFC8126]).
10.3. 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]. 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). If the request comes from within the IETF,
it should be documented in an Internet-Draft. Lastly, the DE must
ensure that any other request for a code point does not conflict with
work that is active or already published within the IETF.
10.4. BGP Extended-Community Registry
IANA has assigned the sub-type 0x1b for "Local Color Mapping (LCM)"
under the "BGP Transitive Opaque Extended-Community" registry under
the "BGP Extended-Community" parameter registry.
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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 coordinating color assignments, since
the IP prefix is unique in the transport network, and hence makes the
color scope also unique and non-conflicting. The color only needs to
be re-mapped into a local color assigned for the same intent (which
is carried in the LCM-EC).
However, if networks under different administrative control establish
a shared transport service between them, where the same transport
service IP address is co-ordinated and shared across the two
networks, then the color assignments associated with that IP address
should also be co-ordinated to avoid any conflicts in either network.
It should be noted that the color assignments coordination are only
necessary for routes specific to the shared service IP. Colors used
for intra-domain or for inter-domain intents associated with the
unique IP addresses do not need any coordination.
Extended communities (LCM-EC/Color-EC) carried in BGP CAR and Service
routes must not be filtered, otherwise the desired intent will not be
achieved.
12. Security Considerations
This extension defines a new SAFI within BGP and therefore does not
change the underlying security issues inherent in the existing BGP
protocol, such as those described in [RFC4271] and [RFC4272].
The extensions defined in this document allows BGP to carry color
aware routes and their associated attributes within a separate BGP
SAFI which is expected to be configured manually by an operator. As
part of configuring a new SAFI, it is implied that the necessary
policy filtering is configured on this SAFI to filter routing
information by the routers participating in this network. Also,
given that this SAFI and these mechanisms can only be enabled through
configuration of routers within a single network, standard security
measures should be taken to restrict access to the management
interface(s) of routers that implement these mechanisms.
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Additionally, BGP sessions SHOULD be protected using TCP
Authentication Option [RFC5925] and the Generalized TTL Security
Mechanism [RFC5082]. To mitigate any risk of manipulating the
routing information carried within a new SAFI, BGP origin validation
[RFC6811] and BGPsec [RFC8205] could be used as means to increase
assurance that the information has not been falsified.
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). Using CAR SAFI
thus provides better security than would be obtained by distributing
the infrastructure routes in existing SAFIs.
BGP CAR distributes label binding similar to [RFC8277] and hence its
security considerations apply. Similarly, BGP CAR distributes
infrastructure IPv6 prefixes and SRv6 SID for SRv6 based CAR and
hence security considerations of section 9.3 of [RFC9252] apply.
As [RFC4272] discusses, BGP is vulnerable to traffic-diversion
attacks. This SAFI routes 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).
In order to mitigate the risk of the diversion of traffic from its
intended destination, existing BGPsec solution could be extended and
supported for this SAFI. The restriction of the applicability of
this SAFI to its intended well-defined scope limits the likelihood of
traffic diversions. Furthermore, as long as the filtering and
appropriate configuration mechanisms discussed above are applied
diligently, risk of the diversion of the traffic is eliminated.
13. Co-authors
Clarence Filsfils
Cisco Systems
Belgium
Email: cfilsfil@cisco.com
Bruno Decraene
Orange
France
Email: bruno.decraene@orange.com
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Luay Jalil
Verizon
USA
Email: luay.jalil@verizon.com
Yuanchao Su
Alibaba, Inc
Email: yitai.syc@alibaba-inc.com
Jim Uttaro
ATT
USA
Email: ju1738@att.com
Jim Guichard
Futurewei
USA
Email: james.n.guichard@futurewei.com
Ketan Talaulikar
Arrcus, Inc
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
14. Contributors
Dirk Steinberg
Lapishills Consulting Limited
Germany
Email: dirk@lapishills.com
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Israel Means
AT&T
USA
Email: im8327@att.com
Reza Rokui
Ciena
USA
Email: rrokui@ciena.com
15. Acknowledgements
The authors would like to acknowledge the review and inputs from many
people.TBD
16. References
16.1. 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>.
[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>.
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[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>.
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[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>.
16.2. Informative References
[I-D.agrawal-spring-srv6-mpls-interworking]
Agrawal, S., Ali, Z., Filsfils, C., Voyer, D., Dawra, G.,
Li, Z., Hegde, S., and S. R. Sangli, "SRv6 and MPLS
interworking", Work in Progress, Internet-Draft, draft-
agrawal-spring-srv6-mpls-interworking-13, 10 January 2024,
<https://datatracker.ietf.org/doc/html/draft-agrawal-
spring-srv6-mpls-interworking-13>.
[I-D.hr-spring-intentaware-routing-using-color]
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-03, 23
October 2023, <https://datatracker.ietf.org/doc/html/
draft-hr-spring-intentaware-routing-using-color-03>.
[I-D.ietf-mpls-seamless-mpls]
Leymann, N., Decraene, B., Filsfils, C., Konstantynowicz,
M., and D. Steinberg, "Seamless MPLS Architecture", Work
in Progress, Internet-Draft, draft-ietf-mpls-seamless-
mpls-07, 28 June 2014,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
seamless-mpls-07>.
[I-D.wang-idr-cpr]
Wang, H., Dong, J., Talaulikar, K., hantao, Chen, R., Xie,
J., and X. Chen, "BGP Colored Prefix Routing (CPR) for
SRv6 based Services", Work in Progress, Internet-Draft,
draft-wang-idr-cpr-03, 20 October 2023,
<https://datatracker.ietf.org/doc/html/draft-wang-idr-cpr-
03>.
[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>.
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[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>.
[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>.
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Appendix A. Illustrations of Service Steering
The following sub-sections illustrate example scenarios of Colored
Service Route Steering over 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 CAR 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 |
| | | |
| ISIS SR | ISIS SR | ISIS SR |
| FA 128 | FA 128 | FA 128 |
+-------------------------+----------------------+---------------------+
iPE iABR eABR ePE
+------+ +------+
|168121| |168231|
+------+ +------+
+------+ +------+ +------+
|168002| |168002| |168002|
+------+ +------+ +------+
+------+ +------+ +------+
|30030 | |30030 | |30030 |
+------+ +------+ +------+
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Figure 6: BGP FA Aware transport CAR path
Use case: Provide end to end intent for service flows.
* With reference to the topology above:
- IGP FA 128 is running in each domain, and mapped to Color C1
- Egress PE E2 advertises a VPN route RD:V/v colored with (color
extended community) 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 and label as
shown above are advertised through border routers in each
domain. When a RR is used in the domain, ADD-PATH is enabled
to advertise multiple available paths.
- On each BGP hop, (E2, C1) next hop is resolved over IGP FA 128
of the domain. AIGP attribute influences BGP CAR route best
path decision as per [RFC7311]. BGP CAR label swap entry is
installed that goes over FA 128 LSP to next hop providing
intent in each IGP domain. Update AIGP metric 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. 168002) carries end to end intent. Thus it
stitches intent over intra domain FA 128.
A.2. E2E BGP transport CAR intent realized using SR Policy
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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) |
| | | |
| | | |
| ISIS SR | ISIS SR | ISIS SR |
+-------------------------+----------------------+--------------------+
iPE iABR eABR ePE
+------+ +------+
| S1 | | S2 |
+------+ +------+
+------+ +------+ +------+
|160121| |160231| | S3 |
+------+ +------+ +------+
+------+ +------+ +------+
|168002| |168002| |168002|
+------+ +------+ +------+
+------+ +------+ +------+
|30030 | |30030 | |30030 |
+------+ +------+ +------+
Figure 7: BGP SR policy Aware transport CAR path
Use case: Provide end to end intent for service flows
* With reference to the topology above:
- SR Policy provide intra domain intent. Below are example SID
lists of SR policies in each domain corresponding to label
stack in Figure 7
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o SR policy (C1,121) segments <S1, 121>
o SR policy (C1,231) segments <S2, 231>
o SR policy (C1,E2) segments <S3, E2>
- Egress PE E2 advertises a VPN route RD:V/v colored with (color
extended community) 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 and label as
shown above are advertised through border routers in each
domain. When a RR is used in the domain, ADD-PATH is enabled
to advertise multiple available paths.
- On each BGP hop, CAR route (E2, C1) next hop is resolved over
an SR policy(C1, next hop). 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. 168002) carries end to end intent. Thus it
stitches intent over intra domain SR policies.
A.3. BGP transport CAR intent realized in a section of the network
A.3.1. Provide intent for service flows only in core domain running
ISIS Flex-Algo
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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 +---+ |
| | | |
| ISIS SR | ISIS SR | ISIS SR |
| Algo 0 | Flex-Algo 128 | Algo 0 |
| Access | Core | Access |
+-------------------------+----------------------+---------------------+
iPE iABR eABR ePE
+------+ +------+
|160121| |168231|
+------+ +------+
+------+ +------+ +------+
|168002| |168002| |160002|
+------+ +------+ +------+
+------+ +------+ +------+
|30030 | |30030 | |30030 |
+------+ +------+ +------+
Figure 8: BGP Hybrid Flex-Algo Aware transport CAR path
* With reference to the topology above:
- IGP FA 128 is only enabled in 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
extended community) C1 to steer traffic via BGP transport CAR
(E2, C1). VPN route propagates via service RRs to ingress PE
E1.
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- BGP CAR route (E2, C1) with next hop, label index and label as
shown above are advertised through border routers in each
domain. When a 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. BGP CAR
label swap entry is installed that goes over algo 0 LSP to next
hop. Update AIGP metric to reflect 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. 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)
* Important:
- IGP Flex-Algo 128 top label provides intent in Core domain.
- BGP CAR label (e.g. 168002) carries intent from PEs which is
realized in core domain
A.3.2. Provide intent for service flows only in core domain over TE
tunnel mesh
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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) +---+ |
| | | |
| | | |
| ISIS/LDP | ISIS/RSVP-TE | ISIS/LDP |
| Access 0 | Core | Access 1 |
+-------------------------+----------------------+-------------------+
iPE iABR eABR ePE
+------+ +------+
|240121| |241231|
+------+ +------+
+------+ +------+ +------+
|242003| |242002| |240002|
+------+ +------+ +------+
+------+ +------+ +------+
|30030 | |30030 | |30030 |
+------+ +------+ +------+
Figure 9: BGP CAR over TE tunnel mesh in core network
* With reference to the topology above:
- RSVP-TE MPLS tunnel mesh is configured only in core (e.g. WAN
network). Access only has ISIS/LDP. (Figure does not show all
TE tunnels).
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- Egress PE E2 advertises a VPN route RD:V/v colored with (color
extended community) 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 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. 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 TE tunnels. 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
domain 0. It steers colored VPN route RD:V/v via (E2, C1).
* Important:
- TE tunnel LSP provides intent in Core domain.
- Dynamic BGP CAR label carries intent from PEs which is realized
in core domain by resolution via TE tunnel.
A.4. Transit 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 include an MPLS LDP network with IGP best-effort; or a
BGP-LU based multi-domain network. MPLS LDP network with best
effort IGP can adopt above scheme. Below is the example for BGP
LU.
* Reference topology:
E1 --- BR1 --- BR2 ......... BR3 ---- BR4 --- E2
Ci <----LU----> Ci
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- Network between BR2 and BR3 comprises of multiple BGP-LU hops
(over IGP-LDP domains).
- E1, BR1, 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
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 of the routes and hence the paths in the
data 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 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 10: BGP CAR resolution over IGP FLex-Algo for resource
avoidance in a domain
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* C1 and C2 represent two unique intents in multi-domain network
- C1 is mapped to "minimize IGP metric"
- 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" and
hence to C1
* Flex-Algo FA129 in Domain 2 is mapped to "minimize IGP metric and
avoid resource R" and hence to C2
* Flex-Algo FA128 in Domain 1 is mapped to "minimize IGP metric"
- There is no resource R to be avoided in Domain 1, hence both C1
and C2 are mapped to FA128
* E1 receives two service routes from E2:
- V/v with BGP Color Extended-Community C1
- W/w with BGP Color Extended-Community C2
* E1 has the following color-aware paths:
- (E2, C1) provided by BGP CAR with the following per-domain
resolution:
o Domain1: over IGP FA128
o Domain2: over IGP FA128
- (E2, C2) provided by BGP CAR with the following per-domain
resolution:
o Domain1: over IGP FA128
o Domain2: 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:
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* 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
This section provides an example of ingress PE per-flow steering as
defined in section 8.6 of [RFC9256] onto BGP CAR routes.
With reference to the 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 the entry 0 is the BGP LU path to N, color C1 is the first
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 etc.) and color them
with an internal per-packet FC variable (0, 1 or 2 in this
example).
* This array is presented as composite candidate path of SR policy
(E2, C100) and acts as a container for grouping constituent paths
of different colors/best effort. This representation provide
automated steering for services colored with Color Extended-
Community C100 via paths of different colors. Note that color
extended community 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 Extended
community C100 to steer traffic via composite SR policy (E2, C100)
i.e. FC array of paths.
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E1 receives three packets K, K1, and K2 on its incoming interface.
These three packets matches on VPN route which recurses on E2. E1
colors these 3 packets respectively with forwarding-class 0, 1, and
2.
As a result
* E1 forwards K along the best effort path to E2 (i.e., for 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 for shared IP addresses
+-------------+ +--------------+
| | | +----|
| |------| | E2 |(IP1)
|----+ | | +----|
| E1 | | | Domain 2 |
|----+ | +--------------+
| | +--------------+
| | | +----|
| Domain 1 |------| | E3 |(IP1)
+-------------+ | +----|
| Domain 3 |
+--------------+
Figure 11: BGP CAR advertisements for shared IP 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 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 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: Anycast with forwarding to nearest
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* Both E2 (in egress domain 2) and E3 (in egress domain 3) advertise
Anycast (shared) IP (IP1, C1) with same 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: Anycast with egress domain visibility at ingress 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 to a set of egress nodes.
* Service route V/v advertised from egress domains D2 and D3 with
colors C1 and 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 belonged to different color
domains, the domains will coordinate the assignment of colors to be
used with shared IP IP1 such that they do not cause conflicts. For
instance, in Example-1 :
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* 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 w.r.t
different color mappings in an inter-domain environment. This
section attempts to enumerate them and provide clarity into the usage
of the color related protocol constructs.
B.1. Single color domain containing network domains with N:N color
distribution
* All network domains (ingress, 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; 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 with N:M 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 resolution may occur via paths of any intra-domain
protocol or even via paths provided by BGP CAR.
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- The 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 Extended-Community 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 end-to-end.
* Any ingress PE that installs a service (VPN) route with a color
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 intents over fewer M intra domain
intents:
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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 | |
| | | |
| ISIS SR | ISIS SR | ISIS SR |
| ACCESS | CORE | ACCESS |
+-----------------------+---------------------+------------------------+
iPE iABR eABR ePE
Figure 12: N:M illustration
* With reference to the topology above:
- Core domain provides 4 intra domain intents as described below:
o FA128 mapped to C10
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o FA129 mapped to C20
o FA130 mapped to C30
o FA131 mapped to C40
- Access domain provides 2 intra domain intents
o FA132 mapped to C1
o FA133 mapped to C2
- Operator defines 4 BGP CAR end to end intents as below
o CAR color C100 that resolves on C1 in access and C10 in core
domain
o CAR color C200 that resolves on C1 in access and C20 in core
domain
o CAR color C300 that resolves on C2 in access and C30 in core
domain
o CAR color C400 that resolves on C2 in access and C40 in 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 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 BGP CAR color is a combination of various intra-domain
colors or intents.
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- 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 resolution mechanism
at both service and transport layers.
B.3. Multiple 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
* 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, following procedures apply:
* The original intent in the BGP CAR route is preserved; i.e. route
is (E, 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 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.
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* A colored service route V/v originated in color domain D1 with
next hop E and color C1 will also have its color extended-
community value 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
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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 | |
| ISISv6 | | ISISv6 |
| FA 128 (B:C12::/32) | |FA128(B:C11::/32)|
| FA 0 (B:02::/32) | |FA0 (B:01::/32) |
+--------------------------------------+ +-----------------+
iPE ASBR ASBR ePE
Figure 13
The topology above is an example to illustrate the BGP CAR SRv6
locator prefix route based design (Routed Service SID:
Section 7.1.1), with hop by hop IPv6 routing within and between
domains.
* Multi-AS network with eBGP CAR session between ASBRs
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* Transport RR (TRR) peers with P, BR and PE clients within an AS to
propagate CAR prefixes. AddPath is enabled to propagate multiple
paths.
* ISIS (IGP) Flex-Algo 128 for SRv6 is running in each AS (AS may
consist of multiple IGP domains)
- 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 ISIS 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 and
PEs through transport RR
* Every router in AS2 resolves BGP CAR prefix B:C11::/32 next hops
IP1 and IP2 in ISISv6 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 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 ISISv6 Flex-Algo 128 in AS1
* Design applies to multiple ASNs. BGP next hop is rewritten across
a eBGP hop.
Important:
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* No tunneling/encapsulation on Ingress PE and BRs for BGP CAR
provided transport.
* Uses longest prefix match of SRv6 service SID to BGP CAR IP
prefix. No mapping to labels/SIDs, instead use of simple IP based
forwarding.
Packet forwarding
@E1: IPv4 VRF V/v => H.Encaps.red <B:C11:2:DT4::> => forward based on
B:C11::/32
@P*: IPv6 table: B:C11::/32 => forward to interface, NH
@121: IPv6 Table: B:C11::/32 => forward to interface, NH
@231: IPv6 table: B:C11:2::/48 :: => forward via ISISv6 FA path to E2
@231: IPv6 Table B:C11:2::/48 => forward via ISISv6 FA path to E2
@E2: My SID table B:C11:2:DT4:: =>pop the outer header and lookup the
inner DA in the VRF
C.2. BGP CAR SRv6 locator reachability distribution with encapsulation
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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 | |
| | | |
| ISISv6 | ISISv6 | ISISv6 |
| 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 14
The topology above is an example to illustrate the BGP CAR SRv6
locator prefix route based design (Routed Service SID:
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
- 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
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- 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 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.)
* AIGP attribute influences BGP CAR route best path decision
* Egress PE E2 advertises a VPN route RD:V/v with SRv6 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
* Uses longest prefix match of SRv6 service SID to BGP CAR prefix.
No mapping labels/SIDs, instead simple IP based forwarding.
* Originating domain PE locators of the given intent can be
summarized on transit BGP hops eliminating per PE state on border
routers.
Packet 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 via ISISv6 FA path to E2
@E2: My SID table B:C11:2:DT4:: =>pop the outer header and lookup the
inner DA in the VRF
C.3. BGP CAR (E, C) route distribution
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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:: |
| | | |
| ISISv6 | ISISv6 | ISISv6 |
| FA 0 (B:03::/32) | FA 0 (B:02::/32) | FA 0(B:01::/32) |
+------------------------+----------------------+---------------------+
iPE iABR eABR ePE
Figure 15
The topology above is an example to illustrate the BGP CAR (E, C)
route based design (Section 7.1.2). The example is iBGP, but 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::>
where z is the node id in egress domain.
* Egress ABRs 231 and 232 redistribute SR policy into BGP CAR NLRI
Type-1 (E2,C2) to other domains, with SRv6 SID of End.B6 behavior.
This route is propagated to ingress PEs through transport RR (TRR)
or inline with 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
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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::>
- SR policy (121, C2) with segments <B:03:x:END::,
B:03:121:END::>
- x and y are node ids within the respective domains
* Egress PE E2 advertises a VPN route RD:V/v with BGP color extended
community 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 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
* Ingress PE steers services via (E,C) CAR route as per [RFC9256]
* In data plane (E,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
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
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@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 the outer header and lookup the
inner DA in the VRF
Appendix D. CAR SAFI NLRI update packing efficiency calculation
CAR SAFI NLRI encoding is optimized for update packing. It allows
per route information (example label, label index and SRv6 SID
encapsulation data) to be carried in non-key TLV part of NLRI. This
allows multiple NLRIs to be packed in single update message when
other attributes are shared. Analysis below shows comparison of
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 considered are ideal packing (maximum number of
routes packed to update message limit of 4k bytes), practical
deployment case with average packing (5 routes share set of BGP path
attributes and hence packed in single update message) and worst-case
of no packing (each route in separate update message).
Summary of ideal, practical and no-packing BGP data in each case
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Encoding | BGP CAR |RFC-8277 style | Result
| NLRI |NLRI |
----------------+--------------+----------------+-----------------------
case a: Label | | |
(Ideal) | 27.5 MB | 26 MB |
+--------------+----------------+ No degradation from
(Practical) | 86 MB | 84 MB | RFC8277 like encoding
+--------------+----------------+
(No packing) | 325 MB | 324 MB |
----------------+--------------+----------------+-----------------------
case b: Label | | 339 MB | CAR SAFI encoding more
& Label-index | | Packing not | efficient by 88% in
(Ideal) | 42 MB | possible | best case and 71% in
+--------------+----------------+ average case over
(Practical) | 99 MB | 339 MB | RFC8277 style encoding
| | Packing not | (which precludes
| | possible | packing)
+--------------+----------------+
(No packing) | 339 MB | 339 MB |
| | |
----------------+--------------+----------------+-----------------------
case c: SRv6 SID| | | Results are similar to
(Ideal) | 49 MB | 378 MB | SR MPLS case.
| | | Transposition provides
+--------------+----------------+ further 20% reduction
(Practical) | 115 MB | 378 MB | in BGP data.
+--------------+----------------+
(No packing) | 378 MB | 378 MB |
----------------+--------------+----------------+-----------------------
Analysis considers 1.5 million routes (5 colors across 300k
endpoints)
case a: BGP data exchanged for non SR MPLS case
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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)
size of update message = (17 * 5) + 200 = 285
Total BGP data on wire = 285 * 300k = ~86MB
No-packing case (1 route per update 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)
size of update message = (16 * 5) + 200 = 280
Total BGP data on wire = 280 * 300k = ~84MB
No-packing case (1 route per update 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
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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
Not supported as label index is encoded in Prefix-SID
Attribute
Practical packing (5 routes in update message)
Not supported as label index is encoded in Prefix-SID
Attribute
No-packing case (1 route per update 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
Rao, et al. Expires 5 August 2024 [Page 85]
Internet-Draft BGP Color-Aware Routing (CAR) February 2024
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)
size of update message
= (30 * 5) + 236 (including Prefix SID) = 386
Total BGP data on wire = 386 * 300k = ~115MB
No-packing case (1 route per update message)
size of update message = 12 + 236 (SID in 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
Not supported as label index is encoded in Prefix-SID
Attribute
Practical packing (5 routes in update message)
Not supported as label index is encoded in Prefix-SID
Attribute
No-packing case (1 route per update 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
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)
size of update message
= (18 * 5) + 236 (including Prefix SID) = 326
Total BGP data on wire = 326 * 300k = ~98MB
No-packing case (1 route per update message)
size of update message
= 12 + 236 (SID in Prefix-SID Attribute) = 252
Total BGP data on wire = 252 * 1.5 million = ~378MB
Authors' Addresses
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Internet-Draft BGP Color-Aware Routing (CAR) February 2024
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
Co-authors
Section 13
Email: dhananjaya.rao@gmail.com
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