IDR Working Group C. Lin Internet Draft New H3C Technologies Intended status: Standards Track Z. Li Expires: July 10, 2024 China Mobile R. Pang China Unicom M. Chen New H3C Technologies January 10, 2024 Segment Routing BGP Egress Peer Engineering over Layer 2 Bundle draft-lin-idr-sr-epe-over-l2bundle-04 Abstract There are deployments where the Layer 3 interface on which a BGP peer session is established is a Layer 2 interface bundle. In order to allow BGP-EPE to control traffic flows on individual member links of the underlying Layer 2 bundle, BGP Peering SIDs need to be allocated to individual bundle member links, and advertisement of such BGP Peering SIDs in BGP-LS is also required. This document describes how to support Segment Routing BGP Egress Peer Engineering over Layer 2 bundle. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on July 10, 2024. Copyright Notice Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents Lin, et al. Expire July 26, 2024 [Page 1] Internet-Draft SR BGP EPE over L2 Bundle January 2024 carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction...................................................2 1.1. Requirements Language.....................................3 2. Problem Statement..............................................3 3. Peer Adjacency Segment for L2 Bundle Member Link...............4 3.1. Advertising in BGP-LS.....................................4 3.2. MPLS-SR Data Plane: L2 Bundle Member PeerAdj SID TLV......5 3.3. SRv6 Data Plane: SRv6 End.X SID TLV.......................6 4. Example........................................................6 4.1. Link Attributes on SR-MPLS Data Plane.....................7 4.2. Link Attributes on SRv6 Data Plane........................8 5. Considerations of Reusing Existing PeerAdj SID TLV.............8 6. Manageability Considerations...................................9 7. Security Considerations........................................9 8. IANA Considerations............................................9 9. References.....................................................9 9.1. Normative References......................................9 9.2. Informative References...................................10 Acknowledgements.................................................10 Authors' Addresses...............................................11 1. Introduction Segment Routing (SR) leverages the source routing paradigm. A node steers a packet through an ordered list of instructions called "segments". Segment Routing can be instantiated on both MPLS and IPv6 data planes, which are referred to as SR-MPLS and SRv6. BGP Egress Peer Engineering (BGP-EPE) allows an ingress Provider Edge (PE) router within the domain to use a specific egress PE and a specific external interface/neighbor to reach a particular destination. The SR architecture [RFC8402] defines three types of BGP Peering Segments that may be instantiated at a BGP node: o Peer Node Segment (PeerNode SID): instruction to steer to a specific peer node Lin, et al. Expires July 10, 2024 [Page 2] Internet-Draft SR BGP EPE over L2 Bundle January 2024 o Peer Adjacency Segment (PeerAdj SID): instruction to steer over a specific local interface towards a specific peer node o Peer Set Segment (PeerSet SID): instruction to load-balance to a set of specific peer nodes [RFC9087] illustrates a centralized controller-based BGP-EPE solution involving SR path computation using the BGP Peering Segments. A centralized controller learns the BGP Peering SIDs via Border Gateway Protocol - Link State (BGP-LS) and then uses this information to program a BGP-EPE policy. [RFC9086] defines the extension to BGP-LS for advertisement of BGP Peering Segments along with their BGP peering node information. There are deployments where the Layer 3 interface on which a BGP peer session is established is a Layer 2 interface bundle (L2 Bundle), for instance, a Link Aggregation Group (LAG) [IEEE802.1AX]. BGP-EPE may wish to control traffic flows on individual member links of the underlying Layer 2 bundle. In order to do so, BGP Peering SIDs need to be allocated to individual bundle member links, and advertisement of such BGP Peering SIDs in BGP-LS is also required. This document describes how to support Segment Routing BGP Egress Peer Engineering over Layer 2 bundle. 1.1. 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. Problem Statement In the network depicted in Figure 1, B and C establish BGP peer session on a Layer 2 bundle. Assume that, the link delays of the members are different because they are over different transport paths, and member link 1 has the lowest delay. The operator of AS1 wishes to apply a BGP-EPE policy to steer the time-sensitive traffic from AS1 to AS2 via member link 1 of the Layer 2 bundle. Lin, et al. Expires July 10, 2024 [Page 3] Internet-Draft SR BGP EPE over L2 Bundle January 2024 L2 Bundle +--------+ /---member 1---\ | | --+---member 2---+--C AS2 | +--------+ / \---member 3---/ | | | |/ +--------+ A AS1 B | |\ +--------+ +--------+ \ | | --------------------D AS3 | | | +--------+ Figure 1: BGP-EPE over L2 Bundle The existing PeerAdj SID can be allocated to the Layer 3 interface between B and C, which is a Layer 2 interface bundle. If steered by that PeerAdj SID, the traffic will be forwarded by load balancing among all the bundle member links. So, the existing mechanism cannot meet the requirement of steering traffic flows via individual member link. 3. Peer Adjacency Segment for L2 Bundle Member Link This document extends Peer Adjacency Segments to be allocated to the individual member links of the Layer 2 interface bundle. The semantics of a Peer Adjacency Segment for L2 Bundle Member Link are: o SR operation: NEXT. o Next-Hop: forwarding across the bundle member link, which the segment is associated with, to the peer connected through the parent L3 interface. On the SR-MPLS data plane, Peer Adjacency Segments for L2 Bundle Member Links are instantiated as MPLS labels. On the SRv6 data plane, Peer Adjacency Segments for L2 Bundle Members are instantiated as SRv6 End.X SIDs. 3.1. Advertising in BGP-LS BGP peering segments are generally advertised in BGP-LS from a BGP node along with its peering topology information, in order to enable computation of efficient BGP-EPE policies and strategies. When advertising Peer Adjacency Segments for L2 Bundle Member Links in BGP-LS, they can be carried in the sub-TLVs of L2 Bundle Member Lin, et al. Expires July 10, 2024 [Page 4] Internet-Draft SR BGP EPE over L2 Bundle January 2024 Attributes TLVs [RFC9085]. Derived from IS-IS advertisements of L2 Bundle [RFC8668], each L2 Bundle Member Attributes TLV identifies an L2 Bundle Member link, which in turn is associated with a parent L3 link. The L3 link is described by the Link NLRI, and the L2 Bundle Member Attributes TLV is associated with the Link NLRI. The L2 Bundle Member Attributes TLV MAY include sub-TLVs that describe attributes associated with the bundle member. In order to advertise Peer Adjacency Segments for L2 Bundle Member Links in BGP-LS, a BGP-LS Link NLRI is advertised to describe the parent L3 link to the BGP peer, which is similar with advertising a PeerAdj SID for the parent L3 link as specified in Section 5.2 of [RFC9086]. Then, multiple L2 Bundle Member Attributes TLVs are included in the Link Attribute TLVs associated with the parent L3 link, each identifying an L2 Bundle member link. The L2 Bundle Member Attributes TLV MUST carry the following sub-TLVs: o SR-MPLS data plane: L2 Bundle Member PeerAdj SID TLV (Type-TBD, defined in Section 3.2) contains a Peer Adjacency Segment for the associated L2 Bundle member link. o SRv6 data plane: SRv6 End.X SID TLV (Type-1106) [RFC9514] contains a Peer Adjacency Segment for the associated L2 Bundle member link. Besides, the L2 Bundle Member Attributes TLV MAY also carry other link attributes describing the associated L2 Bundle member link, such as administrative group (color), link bandwidth, and link delay. When a BGP peer session is established over a Layer 2 interface bundle, an implementation MAY allocate one or more Peer Adjacency Segments for each member link and advertise them in BGP-LS, according to its local configuration and the behavior defined in this document. The inclusion of a L2 Bundle Member Attributes TLV implies that the identified link is a member of the L2 bundle and that the member link is operationally up. If any member link fails, an implementation MUST withdraw the L2 Bundle Member Attributes TLV in BGP-LS, along with the Peer Adjacency Segments for the failed member link. 3.2. MPLS-SR Data Plane: L2 Bundle Member PeerAdj SID TLV On the SR-MPLS data plane, L2 Bundle Member PeerAdj SID TLV is defined to advertise Peer Adjacency Segments for L2 Bundle member links. It has the following format: Lin, et al. Expires July 10, 2024 [Page 5] Internet-Draft SR BGP EPE over L2 Bundle January 2024 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Weight | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID/Label/Index (variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ o Type: TBD. o Length: variable. Valid values are either 7 or 8 based on whether the encoding is done as a SID Index or a label. o Flags: one octet of flags. Same as the Flags field of BGP Peering SIDs TLV, as described in Section 5 of [RFC9086]. o Weight: 1 octet. The value represents the weight of the SID for the purpose of load balancing. o SID/Index/Label. According to the TLV length and the V- and L- Flag settings, it contains either: - A 3-octet local label where the 20 rightmost bits are used for encoding the label value. In this case, the V- and L- Flags MUST be SET. - A 4-octet index defining the offset in the Segment Routing Global Block (SRGB) [RFC8402] advertised by this router. In this case, the SRGB MUST be advertised using the extensions defined in [RFC9085]. 3.3. SRv6 Data Plane: SRv6 End.X SID TLV On the SRv6 data plane, SRv6 End.X SID TLV (Type-1106) [RFC9514] can be used to advertise Peer Adjacency Segments for L2 Bundle member links. 4. Example Take the allocating and advertising of Peer Adjacency Segments on Node B in Figure 1 as an example. B allocates a PeerAdj SID for the Layer 2 interface bundle to peer C, along with a PeerAdj SID for each member link. B programs its forwarding table accordingly: Lin, et al. Expires July 10, 2024 [Page 6] Internet-Draft SR BGP EPE over L2 Bundle January 2024 +===============================+====================+ | PeerAdj SID | Outgoing Interface | +---------------+---------------+ | | IF on SR-MPLS | IF on SRv6 | | | Data Plane | Data Plane | | +===============+===============+====================+ | 1010 | A::A0 | L2 Bundle to C | +---------------+---------------+--------------------+ | 1011 | A::A1 | Member link 1 to C | +---------------+---------------+--------------------+ | 1012 | A::A2 | Member link 2 to C | +---------------+---------------+--------------------+ | 1013 | A::A3 | Member link 3 to C | +---------------+---------------+--------------------+ B signals the related BGP-LS NLRI to the BGP-EPE controller, which is described in the following. Descriptors: o Local Node Descriptors (B's router-ID, ASN-AS1) o Remote Node Descriptors (C's router-ID, ASN-AS2) o Link Descriptors (Link Local/Remote Identifiers describing the Layer 2 bundle, IPv4 or IPv6 Interface Address, IPv4 or IPv6 Neighbor Address) 4.1. Link Attributes on SR-MPLS Data Plane Attributes: o PeerAdj SID TLV (Label-1010) o L2 Bundle Member Attribute TLV (Link Local Identifier describing the member link 1) * L2 Bundle Member PeerAdj SID TLV (Label-1011) * (Optional) Min/Max Unidirectional Link Delay TLV (Delay of member link 1) o L2 Bundle Member Attribute TLV (Link Local Identifier describing the member link 2) * L2 Bundle Member PeerAdj SID TLV (Label-1012) Lin, et al. Expires July 10, 2024 [Page 7] Internet-Draft SR BGP EPE over L2 Bundle January 2024 * (Optional) Min/Max Unidirectional Link Delay TLV (Delay of member link 2) o L2 Bundle Member Attribute TLV (Link Local Identifier describing the member link 3) * L2 Bundle Member PeerAdj SID TLV (Label-1013) * (Optional) Min/Max Unidirectional Link Delay TLV (Delay of member link 3) 4.2. Link Attributes on SRv6 Data Plane Attributes: o SRv6 End.X SID TLV (SID-A::A0) o L2 Bundle Member Attribute TLV (Link Local Identifier describing the member link 1) * SRv6 End.X SID TLV (SID-A::A1) * (Optional) Min/Max Unidirectional Link Delay TLV (Delay of member link 1) o L2 Bundle Member Attribute TLV (Link Local Identifier describing the member link 2) * SRv6 End.X SID TLV (SID-A::A2) * (Optional) Min/Max Unidirectional Link Delay TLV (Delay of member link 2) o L2 Bundle Member Attribute TLV (Link Local Identifier describing the member link 3) * SRv6 End.X SID TLV (SID-A::A3) * (Optional) Min/Max Unidirectional Link Delay TLV (Delay of member link 3) 5. Considerations of Reusing Existing PeerAdj SID TLV The solution in Section 3 defines a new TLV to advertise Peer Adjacency Segment for L2 Bundle member links on SR-MPLS data plane. It may also be possible to reuse the PeerAdj SID TLV defined in [RFC9086]. In this way, the PeerAdj SID TLV will be extended to be included as a sub-TLV of the L2 Bundle Member Attributes TLV. Lin, et al. Expires July 10, 2024 [Page 8] Internet-Draft SR BGP EPE over L2 Bundle January 2024 6. Manageability Considerations The manageability considerations described in [RFC9552] and [RFC9086] also apply to this document. The operator MUST be provided with the options of configuring, enabling, and disabling the advertisement of Peer Adjacency Segment for L2 Bundle member links, as well as control of which information is advertised to which internal or external peer. 7. Security Considerations The security considerations described in [RFC9552] and [RFC9086] also apply to this document. This document does not introduce any new security consideration. 8. IANA Considerations This document defines a new BGP-LS Attribute TLV in the "BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs" registry. +================+============================== | TLV Code Point | Description | +================+==============================+ | TBA | L2 Bundle Member PeerAdj SID | +----------------+------------------------------+ 9. References 9.1. 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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [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, . Lin, et al. Expires July 10, 2024 [Page 9] Internet-Draft SR BGP EPE over L2 Bundle January 2024 [RFC9085] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Gredler, H., and M. Chen, "Border Gateway Protocol - Link State (BGP-LS) Extensions for Segment Routing", RFC 9085, DOI 10.17487/RFC9085, August 2021, . [RFC9086] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Patel, K., Ray, S., and J. Dong, "Border Gateway Protocol - Link State (BGP-LS) Extensions for Segment Routing BGP Egress Peer Engineering", RFC 9086, DOI 10.17487/RFC9086, August 2021, . [RFC9514] Dawra, G., Filsfils, C., Talaulikar, K., Ed., Chen, M., Bernier, D., and B. Decraene, "Border Gateway Protocol - Link State (BGP-LS) Extensions for Segment Routing over IPv6 (SRv6)", RFC 9514, DOI 10.17487/RFC9514, December 2023, . [RFC9552] K. Talaulikar, "Distribution of Link-State and Traffic Engineering Information Using BGP", RFC 9552, DOI 10.17487/RFC9552, December 2023, . 9.2. Informative References [IEEE802.1AX] IEEE, "IEEE Standard for Local and metropolitan area networks -- Link Aggregation", IEEE 802.1AX, . [RFC8668] Ginsberg, L., Ed., Bashandy, A., Filsfils, C., Nanduri, M., and E. Aries, "Advertising Layer 2 Bundle Member Link Attributes in IS-IS", RFC 8668, DOI 10.17487/RFC8668, December 2019, . [RFC9087] Filsfils, C., Ed., Previdi, S., Dawra, G., Ed., Aries, E., and D. Afanasiev, "Segment Routing Centralized BGP Egress Peer Engineering", RFC 9087, DOI 10.17487/RFC9087, August 2021, . Acknowledgements The authors would like to thank Sasha Vainshtein for his review and comments of this document. Lin, et al. Expires July 10, 2024 [Page 10] Internet-Draft SR BGP EPE over L2 Bundle January 2024 Authors' Addresses Changwang Lin New H3C Technologies China Email: linchangwang.04414@h3c.com Zhenqiang Li China Mobile China Email: lizhenqiang@chinamobile.com Ran Pang China Unicom China Email: pangran@chinaunicom.cn Mengxiao Chen New H3C Technologies China Email: chen.mengxiao@h3c.com Lin, et al. Expires July 10, 2024 [Page 11]