RFC 9723

Internet Engineering Task Force (IETF) 💖

Okay so bestie, this is RFC 9723 🎀, and it's giving "BGP Colored Prefix Routing (CPR) for Services Based on Segment Routing over IPv6 (SRv6)" ✨. It's an Informational doc 📚, so it's not a Standards Track spec. It's published for information, not as a must-follow standard. 🦋

Authors: H. Wang, J. Dong, and R. Chen from Huawei Technologies and ZTE Corporation 🌸, plus K. Talaulikar from Cisco Systems 💜 and T. Han from Huawei Technologies. ISSN: 2070-1721. Date: May 2025 💅.

This RFC doesn't obsolete or update any other RFCs, at least not in the title block. 🙈 Okay, let's get into it! 🧚

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Abstract ✨

Okay so the big idea 💅 is a way to advertise IPv6 prefixes in BGP that are tagged with Color Extended Communities 🌈. The whole point is to set up end-to-end intent-aware paths for SRv6 services 🔥. These tagged prefixes are called "Colored Prefixes," and the mechanism is called "Colored Prefix Routing" (CPR) 💜. In SRv6 networks, the Colored Prefixes are the SRv6 locators tied to different intents ⭐. SRv6 services with a specific intent get SRv6 Segment Identifiers (SIDs) under the matching locator, and those get advertised as Colored Prefixes 🦋.

This is slay because the SRv6 service traffic gets steered onto end-to-end intent-aware paths via the longest prefix match of SRv6 Service SIDs against the Colored Prefixes 🎀. It reuses the existing IPv6 Address Family and Color Extended Community, so no new BGP extensions needed 🫶. That makes it easy to interoperate and roll out bit by bit across multi-Autonomous System (AS) networks that are in the same trusted domain 🌸.

Status of This Memo 📜

Not an Internet Standards Track spec, just published for info 💖.

This is an IETF product 🌈. It represents IETF community consensus, got public review, and was approved by the Internet Engineering Steering Group (IESG) ✨. Not every IESG-approved doc is a candidate for any level of Internet Standard, so check Section 2 of RFC 7841 🙈.

Info about the current status, errata, and how to give feedback lives at https://www.rfc-editor.org/info/rfc9723 🔗.

Copyright Notice 💅

Copyright (c) 2025 IETF Trust and the document authors. All rights reserved 🦋.

This doc is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) as of the publication date 📜. Read them carefully, because they spell out your rights and restrictions 💜. Code Components pulled from this doc must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions, and they come without warranty as described in that license 🌸.

Table of Contents 🧚

1.  Introduction
2.  BGP CPR
  2.1.  Colored Prefix Allocation
  2.2.  Colored Prefix Advertisement
  2.3.  CPR to Intra-Domain Path Resolution
  2.4.  SRv6 Service Route Advertisement
  2.5.  SRv6 Service Steering
3.  Encapsulation and Forwarding Process
  3.1.  CPR over SRv6 Intra-Domain Paths
  3.2.  CPR over MPLS Intra-Domain Paths
4.  Operational Considerations
5.  IANA Considerations
6.  Security Considerations
7.  References
  7.1.  Normative References
  7.2.  Informative References
Acknowledgements
Contributors
Authors' Addresses

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1. Introduction 🌈

Okay so more and more, one common network carries lots of different service types 💅, and each one has its own requirements 🎀. Those requirements are basically the service's or customer's "intent," which we represent with an abstract thing called "color" 💖.

When services get delivered across multiple Autonomous Systems (ASes), they need different end-to-end paths to meet their intent 🔥. [INTENTAWARE] covers the problem statements and requirements for inter-domain intent-aware routing 📚.

Inter-domain paths can run on Multi-Protocol Label Switching (MPLS) or the IP data plane 🦋. In MPLS networks, the usual inter-domain move is an end-to-end Label Switched Path (LSP) built with the mechanism in [RFC8277] (usually called BGP-LU, or BGP Labeled Unicast) 🌸. Each domain's ingress border node has to do label swapping for that end-to-end LSP and push the label stack used for the LSP inside its own domain 💜.

In IP networks, BGP can advertise IP reachability info to nodes in different domains 🌐, so all the domain border nodes can learn routes to the IP prefixes of destination nodes in other domains ✨. With SRv6 [RFC8402] [RFC8754] [RFC8986] in the picture, BGP services get SRv6 Service SIDs [RFC9252] 🎀, which are routable in the network based on their SRv6 locator prefix 💅. So the inter-domain path can just be set up from the inter-domain routes to the prefix 🫶. BGP-LU-based inter-domain LSPs are not necessary for IPv6- and SRv6-based networks 🙈.

This doc describes a mechanism that advertises IPv6 prefixes associated with the Color Extended Community to set up end-to-end intent-aware paths for SRv6 services 💖. The color value in that community indicates the intent [RFC9256] 🌈. These IPv6 prefixes are "Colored Prefixes," and the mechanism is Colored Prefix Routing (CPR) 🧚. In SRv6 networks, the Colored Prefixes are the SRv6 locators tied to different intents ⭐. BGP services over SRv6 (e.g., SRv6 VPN services) [RFC9252] with a specific intent can get SRv6 SIDs under the matching locators, which are advertised as Colored Prefixes 🦋. That lets the SRv6 service traffic get steered (as [RFC9252] specifies) onto end-to-end intent-aware paths via longest prefix matching of SRv6 Service SIDs against the Colored Prefixes 💜. In the data plane, no dedicated transport label or SID is needed for the inter-domain path, so the encapsulation overhead is smaller than other options 🍓.

The existing IPv6 Address Family and Color Extended Community can be reused to advertise IPv6 Colored Prefixes without new BGP extensions 🫶. That makes it easy to interoperate and roll out incrementally across multi-AS networks in the same trusted domain (in the sense Section 8 of [RFC8402] uses) 🔐.

2. BGP CPR 💅

2.1. Colored Prefix Allocation 🎀

In SRv6 networks, each node needs an SRv6 locator 💖. To tell N different intents apart, a Provider Edge (PE) node needs N SRv6 locators, each tied to a different intent identified by a color value 🌸. One way to do this is to split the node's base SRv6 locator into N sub-locators, and those sub-locators become Colored Prefixes for different intents 🦋.

Example time 🧚: a PE node gets the base SRv6 Locator 2001:db8:aaaa:1::/64 💜. To provide 16 different intents, that base locator is split into 16 sub-locators, from 2001:db8:aaaa:1:0000::/68 to 2001:db8:aaaa:1:F000::/68 🌈. Each sub-locator maps to a different intent, like low-delay or high-bandwidth ⭐.

Part 1 of 4 done, bestie! 🫶 Say the word and I'll keep going with Section 2.2 💖.

2.2. Colored Prefix Advertisement

okay bestie, so once PE3 has handed out its Colored Prefixes, those routes need to get advertised both inside its own domain AND out to the other domains over BGP ✨ that way the BGP SRv6 service routes can resolve through the matching CPR route 💅

in a multi-AS IPv6 network, the advertising is done using the mechanism in [RFC2545] 🌸 and the family is the Address Family / Subsequent Address Family (AFI/SAFI = 2/1) 🎀. the Color Extended Community [RFC9012] rides along with the Colored Prefix route, and its color value tells you the intent [RFC9256] 🔥. the walkthrough uses this topology 👇

                   Consistent Color Domain:
                           C1, C2, ...
 +--------------+        +--------------+        +-------------+
 |              |        |              |        |             |
 |        [ASBR11]---[ASBR21]      [ASBR23]---[ASBR31]         |
--[PE1] [P1]       |  X     |    [P2]      |   X    |     [P3]  [PE3]--
 |        [ASBR12]---[ASBR22]      [ASBR24]---[ASBR32]         |
 |              |        |              |        |             |
 +--------------+        +--------------+        +-------------+
       AS1                     AS2                     AS3

                                    Colored Prefixes of PE3:
                                         Low delay: PE3:CL1::
                                    High bandwidth: PE3:CL2::
                                                ...

    Figure 1: Example Topology for CPR Route Illustration

so PE3 is set up with two Colored Prefixes, CLP-1 and CLP-2, for two intents, "low-delay" and "high-bandwidth" 😭 and in this example the color for each intent is the same across every domain 🫶

• PE3 originates BGP IPv6 unicast (AFI/SAFI=2/1) routes for PE3:CL1:: and PE3:CL2::. each route should carry its matching Color Extended Community, C1 or C2 💜 PE3 also advertises the base SRv6 Locator prefix PE3:BL, but that one has no Color Extended Community attached 🧚
• ASBR31 and ASBR32 get PE3's CPR routes and pass them on to ASBR23 and ASBR24, with next-hop set to themselves 🦋
• ASBR23 and ASBR24 get PE3's CPR routes too. since AS2's color-to-intent mapping matches AS3's, the Color Extended Community stays unchanged 🌈 they then advertise the CPR routes further into AS2 with next hop set to themselves 🍓
• ASBR21 and ASBR22 act the same way as ASBR31 and ASBR32 👑
• ASBR11 and ASBR12 act the same way as ASBR23 and ASBR24 ✨

normally the color value in the Color Extended Community is consistent across all the domains, so it stays unchanged on the way through 💖 but sometimes one intent gets a different color in different domains 🙈 when that happens, the Color Extended Community needs to be updated at the border nodes according to the color-mapping policy. for example, in AS1 the "low latency" intent is the color "red", but the same intent is the color "blue" in AS2. when a CPR route goes from AS1 to AS2, its Color Extended Community has to change from "red" to "blue" at the border nodes, based on the color-mapping policy 🎀

now, in some networks some of the in-between autonomous systems are MPLS based 🧚‍♀️ the CPR routes can still be advertised with the IPv6 unicast family (AFI/SAFI=2/1) in those MPLS-based intermediate domains. at the MPLS domain border nodes, some route resolution policy can be used to make the CPR routes resolve to intra-domain intent-aware MPLS LSPs 🔥 another option is the IPv6 LU address family (AFI/SAFI=2/4) for advertising the CPR routes in the MPLS domains. the detailed procedure is in Section 7.1.2.1 of [SRv6-INTERWORK] 💅

2.3. CPR to Intra-Domain Path Resolution

a domain border node that receives a CPR route can resolve it to an intra-domain color-aware path based on the tuple (N, C) 🌸 where N is the next hop of the CPR route and C is its Color Extended Community. the intra-domain color-aware path can be built with any of these mechanisms 👇

• SRv6 Policy
• SR-MPLS Policy
• SRv6 Flex-Algo
• SR-MPLS Flex-Algo
• RSVP-TE

for example, if PE1 gets a CPR route to PE3:CL1:: with color C1 and next hop ASBR11, it can resolve the CPR route to an intra-domain SRv6 Policy based on the tuple (ASBR11, C1) 🦋

the intra-domain path resolution scheme can be based on any existing tunnel resolution policy, and new tunnel resolution mechanisms can be introduced if needed 🌈

2.4. SRv6 Service Route Advertisement

for an SRv6 service tied to a specific intent, the SRv6 Service SID can be allocated under the matching Colored locator prefix 💖 for example, on PE3 in the example topology, an SRv6 VPN service with the low-delay intent can get the SRv6 End.DT4 SID PE3:CL1:DT:: 🎀 where PE3:CL1:: is the SRv6 Colored Prefix for low-delay service.

the SRv6 service routes are advertised using the mechanism in [RFC9252] 🔥 the inter-domain VPN Option C is used, which means the next hop of the SRv6 service route is set to the originating PE and is not changed 🫶 since the intent is already embedded in the SRv6 service SID, the SRv6 service route doesn't need to carry the Color Extended Community 💅

2.5. SRv6 Service Steering

with the CPR routing mechanism, the ingress PE that receives the SRv6 service routes follows the SRv6 shortest path forwarding behavior (see Sections 5 and 6 of [RFC9252]) ✨ the SRv6 service SID carried in the service route is used as the destination address in the outer IPv6 header that encapsulates the service packet 🌸 if the matching CPR route has been received and installed, longest prefix matching of SRv6 service SIDs to the Colored Prefixes is performed 👑 as a result of that prefix match, the next hop found is an intra-domain color-aware path, and that path is used to forward the SRv6 service traffic 💜 this process repeats at the border node of each domain the packet crosses, until it reaches its destination 🌈

3. Encapsulation and Forwarding Process

this section covers the encapsulation and forwarding process for data packets that match the corresponding CPR route 🧚

the topology of Figure 1 is used in each example 🍓

3.1. CPR over SRv6 Intra-Domain Paths

here's the packet encapsulation and forwarding process for CPR over SRv6 Policy 💖 it uses the abstract representation of IPv6 and the Segment Routing Header (SRH) described in Section 6 of [RFC8754] 🎀

PE3 is provisioned with the Colored Prefix PE3:CL1:: for "low-delay" 🔥

• in AS1, the SRv6 Policy on PE1 for (ASBR11, C1) is represented with SID list <P1, ASBR11> 🫶
• in AS2, the SRv6 Policy on ASBR21 for (ASBR23, C1) is represented with the SID list <P2, ASBR23> 💅
• in AS3, the SRv6 Policy on ASBR31 for (PE3, C1) is represented with the SID list <P3, PE3> ✨

C-pkt is the customer packet PE1 received from its attaching CE 🌸

for packets that belong to an SRv6 VPN service associated with the SRv6 Service SID PE3:CL1.DT6, the encapsulation and forwarding uses the H.Encaps.Red behavior [RFC8986] 👑 it looks like this 👇

PE1 ->P1:           (PE1, P1)(PE3:CL1.DT6, ASBR11; SL=2)(C-pkt)
P1 ->ASBR11:    (PE1, ASBR11)(PE3:CL1.DT6, ASBR11; SL=1)(C-pkt)
ASBR11->ASBR21:                       (PE1, PE3:CL1.DT6)(C-pkt)
ASBR21->P2: (ASBR21, P2)(ASBR23; SL=1)(PE1, PE3:CL1.DT6)(C-pkt)
P2->ASBR23:           (ASBR21, ASBR23)(PE1, PE3:CL1.DT6)(C-pkt)
ASBR23->ASBR31:                       (PE1, PE3:CL1.DT6)(C-pkt)
ASBR31->P3:    (ASBR31, P3)(PE3; SL=1)(PE1, PE3:CL1.DT6)(C-pkt)
P3->PE3:                 (ASBR31, PE3)(PE1, PE3:CL1.DT6)(C-pkt)

                              Figure 2

in some autonomous systems, SRv6 Flex-Algo may be used to provide intent-aware intra-domain paths 🦋 the encapsulation is similar to the SRv6 Policy case 🌈

3.2. CPR over MPLS Intra-Domain Paths

in networks where some autonomous systems use the MPLS-based data plane, the CPR route can be resolved over a color-aware intra-domain MPLS LSP 🧚‍♀️ that kind of LSP may be set up using SR-MPLS Policy, SR-MPLS Flex-Algo, or RSVP-TE 💖

the encapsulation and forwarding of SRv6 service packets (which are actually IPv6 packets) over an intra-domain MPLS LSP is based on the MPLS mechanisms defined in [RFC3031], [RFC3032] and [RFC8660] 🔥 the behavior is similar to IPv6 Provider Edge Routers (6PEs) [RFC4798] 💅

• in AS1, the SR-MPLS Policy on PE1 for (ASBR11, C1) is represented with SID list <P1, ASBR11> 🎀
• in AS2, the SR-MPLS Flex-Algo on ASBR21 for (ASBR23, C1) is represented with SID list <ASBR23> ✨
• in AS3, the SR-MPLS Policy on ASBR31 for (PE3, C1) is represented with SID list <P3, PE3> 🌸

C-pkt is the customer packet PE-1 received from its attaching CE 🫶

for packets that belong to an SRv6 VPN service associated with the SRv6 Service SID PE3:CL1.DT6, the encapsulation and forwarding process goes like this 👇

PE1-> P1: Label-stack(P1, ASBR11)(PE1, PE3:CL1.DT6)(C-pkt)
P1->ASBR11:   Label-stack(ASBR11)(PE1, PE3:CL1.DT6)(C-pkt)
ASBR11->ASBR21:                  (PE1, PE3:CL1.DT6)(C-pkt)
ASBR21->P2:   Label-stack(ASBR23)(PE1, PE3:CL1.DT6)(C-pkt)
P2->ASBR23:   Label-stack(ASBR23)(PE1, PE3:CL1.DT6)(C-pkt)
ASBR23->ASBR31:                  (PE1, PE3:CL1.DT6)(C-pkt)
ASBR31->P3:  Label-stack(P3, PE3)(PE1, PE3:CL1.DT6)(C-pkt)
P3->PE3:         Label-stack(PE3)(PE1, PE3:CL1.DT6)(C-pkt)

Figure 3

4. Operational Considerations 💅

Okay bestie, so the CPR mechanism is giving for two kinds of situations. The first is when several interconnected ASes all belong to the same operator 🏢. The second is when ASes from different operators have an operational trust model between them, which means they count as the same trusted domain (in the sense used by Section 8 of [RFC8402]) 🤝.

As described in Section 5 of [INTENTAWARE], inter-domain intent-aware routing can be achieved with a logical tunnel made by an SR Policy that covers multiple ASes 🚇. Service traffic with a specific intent can also be steered onto that inter-domain SR Policy, based on the intent signaled by the Color Extended Community 🎯. An operator might prefer a BGP routing-based solution for the reasons in [INTENTAWARE] 🤔. They could also look at an inter-domain controller for end-to-end intent-aware path computation 🧠. This document proposes an alternate way to signal intent: IPv6 Colored Prefixes using BGP 🌈.

When Colored Prefixes are assigned as sub-locators of the node's base SRv6 locator, the IPv6 unicast route of the base locator prefix is the prefix that covers all of the Colored locator prefixes 📦. So, to make sure the Colored locator prefixes can be distributed to the ingress PE nodes along the border nodes, route aggregation is required to be disabled for IPv6 unicast routes that carry the Color Extended Community 🚫🧩.

With the CPR mechanism, at the prefix originator, each Colored Prefix is associated with one specific intent (i.e., color) 🎨. In each domain, according to the color mapping policy, the same CPR route is always updated with the same color 🔁. Having multiple copies of CPR routes with the same Colored Prefix but different Color Extended Community is considered a misconfiguration 🙅‍♀️.

All the border nodes and the ingress PE nodes need to install the Colored locator prefixes in the RIB and FIB 💾. For transit domains that support the CPR mechanism, the border nodes can use the tuple (N, C), where N is the next hop and C is the color, to resolve the CPR routes to intent-aware intra-domain paths 🛣️. For transit domains that do not support the CPR mechanism, the border nodes would ignore the Color Extended Community and resolve the CPR routes over a best-effort intra-domain path to the next-hop N. Meanwhile the CPR route is advertised further to the downstream domains with only the next hop changed to itself 🙈. This means the CPR routes can resolve to intent-aware intra-domain paths in any autonomous systems that support the CPR mechanism, and they can fall back to best-effort intra-domain paths in the legacy autonomous systems 🔙✨.

There may be multiple inter-domain links between adjacent autonomous systems, and a border node BGP speaker may receive CPR routes from multiple peering BGP speakers in another domain via External BGP (EBGP) 🔗. A BGP speaker's local policy can take the attributes of the inter-domain links and the attributes of the received CPR routes into account when picking the best path for specific Colored Prefixes, so the choice better meets the intent 🎯. The detailed local policy is outside the scope of this document. In a multi-AS environment, though, the policy of BGP speakers in different domains needs to be consistent 🤝💜.

In this document, the IPv6 Unicast Address Family is used for advertising IPv6 Colored Prefixes. The big win here is better interoperability with legacy networks that can't support intent-aware paths yet, plus easier incremental deployment of intent-aware routing 🪜🌸. There is one potential concern: separating Colored Prefixes from public IPv6 unicast routes. The IP prefixes and SRv6 locators of network infrastructure are usually advertised as part of the IP unicast routes, and appropriate filters are configured at the boundaries of network administration, so this concern is not considered to be a significant issue 😌. [RFC9602] allocates 5f00::/16 for SRv6 SIDs. By common agreement among the participants in the trusted domain, the filters can be configured to by default drop all traffic from 5f00::/16 but permit the Colored Prefixes in use in these domains 🛡️. The proposal in [BGP-CAR] is a complementary solution, also based on color indicating the intent, where the SRv6 Locator prefix itself signifies the intent. The difference is that it uses a separate SAFI 🦋.

[BGP-CT] describes another mechanism for intent-aware routing. Here the SRv6 service SIDs are not directly associated with the intent, so additional SRv6 transport SIDs are required to steer traffic to the inter-domain intent-aware paths. It also needs an SRv6 operation similar to MPLS label swapping on the border nodes of autonomous systems 🔁🧚.

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5. IANA Considerations 🌷

Good news, nothing to do for IANA here! This document has no IANA actions 🙌.

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6. Security Considerations 🔐

Okay, this part is important, so pay attention 👀. The mechanism in this document gives an approach to inter-domain intent-aware routing that is based on existing BGP protocol mechanisms. It reuses the existing BGP IPv6 Unicast Address Family and the existing Color Extended Community, with no further BGP extensions needed 🧩. With this approach, the number of IPv6 Colored Prefixes advertised by PE nodes is proportionate to the number of intents it supports. That can add extra routes to the BGP IPv6 routing table 📈. But these are infrastructure routes, so the number of Colored Prefixes is only a small slice of the total amount of IPv6 prefixes. Thus, the impact on the required routing table size is considered acceptable 👍.

Now for the spicy part 🌶️💀. As the CPR routes are distributed across multiple ASes that belong to a trusted domain, the mapping relationship between the intent and the IPv6 Colored Prefixes is observable to BGP nodes in those ASes. It is possible for an on-path attacker in the trusted domain to identify packets associated with a particular intent 😱. Literally a privacy leak in the making, so keep that in mind when you deploy this!

The security considerations described in [RFC4271], [RFC4272], and [RFC8754] apply to this document 🔒.

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7. References 📚

7.1. Normative References

   [RFC2545]  Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol
              Extensions for IPv6 Inter-Domain Routing", RFC 2545,
              DOI 10.17487/RFC2545, March 1999,
              <https://www.rfc-editor.org/info/rfc2545>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC4272]  Murphy, S., "BGP Security Vulnerabilities Analysis",
              RFC 4272, DOI 10.17487/RFC4272, January 2006,
              <https://www.rfc-editor.org/info/rfc4272>.

   [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>.

   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
              <https://www.rfc-editor.org/info/rfc8754>.

   [RFC8986]  Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
              D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
              (SRv6) Network Programming", RFC 8986,
              DOI 10.17487/RFC8986, February 2021,
              <https://www.rfc-editor.org/info/rfc8986>.

   [RFC9012]  Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
              "The BGP Tunnel Encapsulation Attribute", RFC 9012,
              DOI 10.17487/RFC9012, April 2021,
              <https://www.rfc-editor.org/info/rfc9012>.

   [RFC9252]  Dawra, G., Ed., Talaulikar, K., Ed., Raszuk, R., Decraene,
              B., Zhuang, S., and J. Rabadan, "BGP Overlay Services
              Based on Segment Routing over IPv6 (SRv6)", RFC 9252,
              DOI 10.17487/RFC9252, July 2022,
              <https://www.rfc-editor.org/info/rfc9252>.

   [RFC9256]  Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
              A., and P. Mattes, "Segment Routing Policy Architecture",
              RFC 9256, DOI 10.17487/RFC9256, July 2022,
              <https://www.rfc-editor.org/info/rfc9256>.

7.2. Informative References

   [BGP-CAR]  Rao, D., Ed. and S. Agrawal, Ed., "BGP Color-Aware Routing
              (CAR)", Work in Progress, Internet-Draft, draft-ietf-idr-
              bgp-car-16, 20 February 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
              car-16>.

   [BGP-CT]   Vairavakkalai, K., Ed. and N. Venkataraman, Ed., "BGP
              Classful Transport Planes", Work in Progress, Internet-
              Draft, draft-ietf-idr-bgp-ct-39, 28 February 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
              ct-39>.

   [INTENTAWARE]
              Hegde, S., Rao, D., Uttaro, J., Bogdanov, A., and L.
              Jalil, "Problem statement for Inter-domain Intent-aware
              Routing using Color", Work in Progress, Internet-Draft,
              draft-hr-spring-intentaware-routing-using-color-04, 31
              January 2025, <https://datatracker.ietf.org/doc/html/
              draft-hr-spring-intentaware-routing-using-color-04>.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,
              <https://www.rfc-editor.org/info/rfc3031>.

   [RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
              Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
              Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
              <https://www.rfc-editor.org/info/rfc3032>.

   [RFC4798]  De Clercq, J., Ooms, D., Prevost, S., and F. Le Faucheur,
              "Connecting IPv6 Islands over IPv4 MPLS Using IPv6
              Provider Edge Routers (6PE)", RFC 4798,
              DOI 10.17487/RFC4798, February 2007,
              <https://www.rfc-editor.org/info/rfc4798>.

   [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>.

   [RFC8660]  Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing with the MPLS Data Plane", RFC 8660,
              DOI 10.17487/RFC8660, December 2019,
              <https://www.rfc-editor.org/info/rfc8660>.

   [RFC9602]  Krishnan, S., "Segment Routing over IPv6 (SRv6) Segment
              Identifiers in the IPv6 Addressing Architecture",
              RFC 9602, DOI 10.17487/RFC9602, October 2024,
              <https://www.rfc-editor.org/info/rfc9602>.

   [SRv6-INTERWORK]
              Agrawal, S., Ed., Filsfils, C., Voyer, D., Dawra, G., Li,
              Z., and S. Hegde, "SRv6 and MPLS interworking", Work in
              Progress, Internet-Draft, draft-ietf-spring-srv6-mpls-
              interworking-00, 17 October 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-spring-
              srv6-mpls-interworking-00>.

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Acknowledgements 🫶

Huge thanks to Shunwan Zhuang, Zhibo Hu, Zhenbin Li, Dhananjaya Rao, and Dhruv Dhody for reviewing and for all the valuable discussion 💖✨.

Contributors ✨

okay so these three people put SO much work into this doc 🫶 they should be counted as co-authors, no cap

Xinjun Chen
Email: ifocus.chen@huawei.com


Jingrong Xie
Email: xiejingrong@huawei.com


Zhenqiang Li
Email: li_zhenqiang@hotmail.com

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Authors' Addresses 💖

and here are the authors, bestie 🌸 with where to find each of them 💅

Haibo Wang
Huawei Technologies
China
Email: rainsword.wang@huawei.com


Jie Dong
Huawei Technologies
China
Email: jie.dong@huawei.com


Ketan Talaulikar
Cisco Systems
India
Email: ketant.ietf@gmail.com


Tao Han
Huawei Technologies
China
Email: hantao@huawei.com


Ran Chen
ZTE Corporation
China
Email: chen.ran@zte.com.cn