Inter-Domain Routing G. Dawra Internet-Draft LinkedIn Intended status: Standards Track C. Filsfils Expires: May 14, 2022 K. Talaulikar, Ed. Cisco Systems M. Chen Huawei D. Bernier Bell Canada B. Decraene Orange November 10, 2021 BGP Link State Extensions for SRv6 draft-ietf-idr-bgpls-srv6-ext-09 Abstract Segment Routing over IPv6 (SRv6) allows for a flexible definition of end-to-end paths within various topologies by encoding paths as sequences of topological or functional sub-paths, called "segments". These segments are advertised by various protocols such as BGP, IS-IS and OSPFv3. This document defines extensions to BGP Link-state (BGP-LS) to advertise SRv6 segments along with their behaviors and other attributes via BGP. The BGP-LS address-family solution for SRv6 described in this document is similar to BGP-LS for SR for the MPLS data-plane defined in a separate document. 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 May 14, 2022. Dawra, et al. Expires May 14, 2022 [Page 1] Internet-Draft BGP-LS Extensions for SRv6 November 2021 Copyright Notice Copyright (c) 2021 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 (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents 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 . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. BGP-LS Extensions for SRv6 . . . . . . . . . . . . . . . . . 4 3. SRv6 Node Attributes . . . . . . . . . . . . . . . . . . . . 5 3.1. SRv6 Capabilities TLV . . . . . . . . . . . . . . . . . . 5 3.2. SRv6 Node MSD Types . . . . . . . . . . . . . . . . . . . 6 4. SRv6 Link Attributes . . . . . . . . . . . . . . . . . . . . 6 4.1. SRv6 End.X SID TLV . . . . . . . . . . . . . . . . . . . 7 4.2. SRv6 LAN End.X SID TLV . . . . . . . . . . . . . . . . . 8 4.3. SRv6 Link MSD Types . . . . . . . . . . . . . . . . . . . 10 5. SRv6 Prefix Attributes . . . . . . . . . . . . . . . . . . . 10 5.1. SRv6 Locator TLV . . . . . . . . . . . . . . . . . . . . 10 6. SRv6 SID NLRI . . . . . . . . . . . . . . . . . . . . . . . . 12 6.1. SRv6 SID Information TLV . . . . . . . . . . . . . . . . 13 7. SRv6 SID Attributes . . . . . . . . . . . . . . . . . . . . . 14 7.1. SRv6 Endpoint Behavior TLV . . . . . . . . . . . . . . . 14 7.2. SRv6 BGP Peer Node SID TLV . . . . . . . . . . . . . . . 15 8. SRv6 SID Structure TLV . . . . . . . . . . . . . . . . . . . 16 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 9.1. BGP-LS NLRI-Types . . . . . . . . . . . . . . . . . . . . 17 9.2. BGP-LS TLVs . . . . . . . . . . . . . . . . . . . . . . . 17 9.3. SRv6 BGP EPE SID Flags . . . . . . . . . . . . . . . . . 18 10. Manageability Considerations . . . . . . . . . . . . . . . . 18 11. Security Considerations . . . . . . . . . . . . . . . . . . . 19 12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 20 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 14.1. Normative References . . . . . . . . . . . . . . . . . . 21 14.2. Informative References . . . . . . . . . . . . . . . . . 22 Appendix A. Differences with BGP-EPE for SR-MPLS . . . . . . . . 23 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 Dawra, et al. Expires May 14, 2022 [Page 2] Internet-Draft BGP-LS Extensions for SRv6 November 2021 1. Introduction SRv6 refers to Segment Routing instantiated on the IPv6 data-plane [RFC8402]. An SRv6 Segment is often referred to by its SRv6 Segment Identifier (SID). The network programming paradigm [RFC8986] is central to SRv6. It describes how different behaviors can be bound to SIDs and how a network program can be expressed as a combination of SIDs. An SRv6-capable node N maintains all the SRv6 segments explicitly instantiated at node N. The IS-IS and OSPFv3 link-state routing protocols have been extended to advertise some of these SRv6 SIDs and SRv6-related information [I-D.ietf-lsr-isis-srv6-extensions], [I-D.ietf-lsr-ospfv3-srv6-extensions]. Other SRv6 SIDs may be instantiated on a node via other mechanisms for topological or service functionalities. The advertisement of SR related information along with the topology for the MPLS data-plane instantiation (SR-MPLS) is specified in [RFC9085] and for the BGP Egress Peer Engineering (EPE) is specified in [RFC9086]. On similar lines, introducing the SRv6 related information in BGP-LS allows consumer applications that require topological visibility to also receive the SRv6 SIDs from nodes across an IGP domain or even across Autonomous Systems (AS), as required. This allows applications to leverage the SRv6 capabilities for network programming. The identifying key of each Link-State object, namely a node, link, or prefix, is encoded in the Network-Layer Reachability Information (NLRI) and the properties of the object are encoded in the BGP-LS Attribute [RFC7752]. This document describes extensions to BGP-LS to advertise the SRv6 SIDs and other SRv6 information from all the SRv6 capable nodes in the IGP domain when sourced from link-state routing protocols and directly from individual SRv6 capable nodes (e.g. when sourced from BGP for EPE). 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. Dawra, et al. Expires May 14, 2022 [Page 3] Internet-Draft BGP-LS Extensions for SRv6 November 2021 2. BGP-LS Extensions for SRv6 BGP-LS [RFC7752] defines the Node, Link, and Prefix Link-State Network Layer Reachability Information (NLRI) types and the advertisement of their attributes via BGP. When the BGP-LS router is advertising topology information that it sources from the underlying link-state routing protocol (as described in [RFC7752]), then it maps the corresponding SRv6 information from the SRv6 extensions for IS-IS [I-D.ietf-lsr-isis-srv6-extensions] and OSPFv3 [I-D.ietf-lsr-ospfv3-srv6-extensions] protocols to their BGP- LS TLVs/sub-TLVs for all SRv6 capable nodes in that routing protocol domain. When the BGP-LS router is advertising topology information from the BGP routing protocol (e.g., for EPE as described in [RFC9086]), then it advertises the SRv6 information from the local node alone. The SRv6 information pertaining to a node is advertised via the BGP- LS Node NLRI and using the BGP-LS Attribute TLVs as follows: o SRv6 Capabilities of the node are advertised via the SRv6 Capabilities TLV (Section 3.1). o Maximum SID Depth (MSD) types introduced for SRv6 are advertised (Section 3.2) using the Node MSD TLV specified in [RFC8814] o Algorithm support for SRv6 is advertised via the SR Algorithm TLV specified in [RFC9085]. The SRv6 information pertaining to a link is advertised via the BGP- LS Link NLRI and using the BGP-LS Attribute TLVs as follows: o SRv6 SID of the IGP Adjacency SID or the BGP EPE Peer Adjacency SID [RFC8402] is advertised via the SRv6 End.X SID TLV introduced in this document (Section 4.1). o SRv6 SID of the IGP Adjacency SID to a non-Designated Router (DR) or non-Designated Intermediate-System (DIS) [RFC8402] is advertised via the SRv6 LAN End.X SID TLV introduced in this document (Section 4.2). o MSD types introduced for SRv6 are advertised (Section 4.3) using the Link MSD TLV specified in [RFC8814]. The SRv6 information pertaining to a prefix is advertised via the BGP-LS Prefix NLRI and using the BGP-LS Attribute TLVs as follows: Dawra, et al. Expires May 14, 2022 [Page 4] Internet-Draft BGP-LS Extensions for SRv6 November 2021 o SRv6 Locator is advertised via the SRv6 Locator TLV introduced in this document (Section 5.1). o The attributes of the SRv6 Locator are advertised via the Prefix Attribute Flags TLV specified in [RFC9085]. The SRv6 SIDs associated with the node are advertised using the BGP- LS SRv6 SID NLRI introduced in this document (Section 6). This enables the BGP-LS encoding to scale to cover a potentially large set of SRv6 SIDs instantiated on a node with the granularity of individual SIDs and without affecting the size and scalability of the BGP-LS updates. Had the SRv6 SIDs been advertised within the BGP-LS Link Attribute associated with the existing Node NLRI, the BGP-LS update would have grown rather large with the increase in SRv6 SIDs on the node and would have also required a large update message to be generated for any change to even a single SRv6 SID. BGP-LS Attribute TLVs for the SRv6 SID NLRI are introduced in this document as follows: o The endpoint behavior of the SRv6 SID is advertised via the SRv6 Endpoint Behavior TLV (Section 7.1). o The BGP EPE Peer Node context for a Peer Node, and the Peer Set context for a Peer Set SID [RFC8402] are advertised via the SRv6 BGP EPE Peer Node SID TLV (Section 7.2), Subsequent sections of this document specify the encoding and usage of these extensions. All the TLVs introduced follow the formats and common field definitions provided in [RFC7752]. 3. SRv6 Node Attributes SRv6 attributes of a node are advertised using the BGP-LS Attribute TLVs defined in this section and associated with the BGP-LS Node NLRI. 3.1. SRv6 Capabilities TLV This BGP-LS Attribute TLV is used to announce the SRv6 capabilities of the node along with the BGP-LS Node NLRI and indicates the SRv6 support by the node. A single instance of this TLV MUST be included in the BGP-LS attribute for each SRv6 capable node. This TLV maps from the SRv6 Capabilities sub-TLV [I-D.ietf-lsr-isis-srv6-extensions] and the SRv6 Capabilities TLV [I-D.ietf-lsr-ospfv3-srv6-extensions] of the IS-IS and OSPFv3 protocol SRv6 extensions respectively. Any sub-TLVs introduced by future documents for IS-IS and OSPFv3 SRv6 Capabilities are REQUIRED to be introduced as top-level TLVs in BGP-LS in the future. Dawra, et al. Expires May 14, 2022 [Page 5] Internet-Draft BGP-LS Extensions for SRv6 November 2021 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 | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: SRv6 Capabilities TLV Format Where: o Type: 1038 o Length : 4. o Flags: 2 octet field. The flags are derived from the SRv6 Capabilities sub-TLV/TLV of IS-IS (section 2 of [I-D.ietf-lsr-isis-srv6-extensions]) and OSPFv3 (section 2 of [I-D.ietf-lsr-ospfv3-srv6-extensions]). o Reserved: 2 octet that MUST be set to 0 and ignored on receipt. 3.2. SRv6 Node MSD Types The Node MSD TLV [RFC8814] of the BGP-LS Attribute of the Node NLRI is also used to advertise the limits and the Segment Routing Header (SRH) [RFC8754] operations supported by the SRv6 capable node. The SRv6 MSD Types specified in section 4 of [I-D.ietf-lsr-isis-srv6-extensions] are also used with the BGP-LS Node MSD TLV as these codepoints are shared between IS-IS, OSPF and BGP-LS protocols. The description and semantics of these new MSD types for BGP-LS are identical as specified in [I-D.ietf-lsr-isis-srv6-extensions]. Each MSD type is encoded as a one-octet type followed by a one-octet value as specified in [RFC8814]. 4. SRv6 Link Attributes SRv6 attributes and SIDs associated with a link or adjacency are advertised using the BGP-LS Attribute TLVs defined in this section and associated with the BGP-LS Link NLRI. Dawra, et al. Expires May 14, 2022 [Page 6] Internet-Draft BGP-LS Extensions for SRv6 November 2021 4.1. SRv6 End.X SID TLV The SRv6 End.X SID TLV is used to advertise the SRv6 SIDs associated with an IGP Adjacency SID behavior that correspond to a point-to- point or point-to-multipoint link or adjacency of the node running IS-IS and OSPFv3 protocols. This TLV can also be used to advertise the SRv6 SID corresponding to the underlying layer-2 member links for a layer-3 bundle interface as a sub-TLV of the L2 Bundle Member Attribute TLV [RFC9085]. The SRv6 SID for the IGP adjacency using the End.X behaviors (viz. End.X, End.X with Penultimate Segment Pop of the SRH (PSP), End.X with Ultimate Segment Pop of the SRH (USP), and End.X with PSP & USP) [RFC8986] are advertised using the SRv6 End.X SID TLV. This TLV is also used by BGP-LS to advertise the BGP EPE Peer Adjacency SID for SRv6 on the same lines as specified for SR-MPLS in [RFC9086]. The SRv6 SID for the BGP Peer Adjacency using End.X behaviors (viz. End.X, End.X with PSP, End.X with USP, and End.X with PSP & USP) [RFC8986] indicates the cross-connect to a specific layer-3 link to the specific BGP session peer (neighbor). The TLV 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Endpoint Behavior | Flags | Algorithm | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Weight | Reserved | SID (16 octets) ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont ...) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont ...) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont ...) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont ...) | Sub-TLVs (variable) . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: SRv6 End.X TLV Format Where: Type: 1106 Dawra, et al. Expires May 14, 2022 [Page 7] Internet-Draft BGP-LS Extensions for SRv6 November 2021 Length: variable Endpoint Behavior: 2 octet field. The Endpoint Behavior code point for this SRv6 SID as defined in section 10.2 of [RFC8986]. Flags: 1 octet of flags. The flags are derived from the SRv6 End.X SID sub-TLV/TLV of IS-IS (section 8.1 of [I-D.ietf-lsr-isis-srv6-extensions]) and OSPFv3 (section 8.1 of [I-D.ietf-lsr-ospfv3-srv6-extensions]). In the case of BGP EPE Peer Adjacency SID, the flags are as defined for the SRv6 BGP Peer Node SID TLV (Section 7.2). Algorithm: 1 octet field. Algorithm associated with the SID. Algorithm values are defined in the IANA IGP Algorithm Type registry (https://www.iana.org/assignments/igp-parameters/igp- parameters.xhtml). Weight: 1 octet field. The value represents the weight of the SID for the purpose of load balancing. The use of the weight is defined in [RFC8402]. Reserved: 1 octet field that MUST be set to 0 and ignored on receipt. SID: 16 octet field. This field encodes the advertised SRv6 SID as 128 bit value. Sub-TLVs : They are allocated from the IANA "BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs" registry and are used to advertise sub-TLVs that provide additional attributes for the specific SRv6 SID. This document defines one inSection 8. 4.2. SRv6 LAN End.X SID TLV For a LAN interface, an IGP node announces normally only its adjacency to the IS-IS pseudo-node (or the equivalent OSPF DR). The SRv6 LAN End.X SID TLV allows a node to announce the SRv6 SID corresponding to its adjacencies to all other (i.e., non-DIS or non- DR) nodes attached to the LAN in a single instance of the BGP-LS Link NLRI. Without this TLV, multiple BGP-LS Link NLRIs would need to be originated for each additional adjacency to advertise the SRv6 End.X SID TLVs for these neighbor adjacencies. The SRv6 SID for these IGP adjacencies using the End.X behaviors (viz. End.X, End.X with PSP, End.X with USP, and End.X with PSP & USP) [RFC8986] are advertised using the SRv6 LAN End.X SID TLV. Dawra, et al. Expires May 14, 2022 [Page 8] Internet-Draft BGP-LS Extensions for SRv6 November 2021 The BGP-LS IS-IS SRv6 LAN End.X SID and BGP-LS OSPFv3 SRv6 LAN End.X SID TLVs have 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Endpoint Behavior | Flags | Algorithm | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Weight | Reserved | Neighbor ID - | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | IS-IS System-ID (6 octets) or OSPFv3 Router-ID (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (16 octets) ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont ...) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont ...) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont ...) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-TLVs (variable) . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: SRv6 LAN End.X SID TLV Format Where: o Type: 1107 in case of IS-IS and 1108 in case of OSPFv3 o Length: variable o Endpoint Behavior: 2 octet field. The Endpoint Behavior code point for this SRv6 SID as defined in section 10.2 of [RFC8986]. o Flags: 1 octet of flags. The flags are derived from the SRv6 LAN End.X SID sub-TLV/TLV of IS-IS (section 8.2 of [I-D.ietf-lsr-isis-srv6-extensions]) and OSPFv3 (section 8.2 of [I-D.ietf-lsr-ospfv3-srv6-extensions]). o Algorithm: 1 octet field. Algorithm associated with the SID. Algorithm values are defined in the IANA IGP Algorithm Type registry (https://www.iana.org/assignments/igp-parameters/igp- parameters.xhtml). Dawra, et al. Expires May 14, 2022 [Page 9] Internet-Draft BGP-LS Extensions for SRv6 November 2021 o Weight: 1 octet field. The value represents the weight of the SID for the purpose of load balancing. The use of the weight is defined in [RFC8402]. o Reserved: 1 octet field that MUST be set to 0 and ignored on receipt. o Neighbor ID : 6 octets of IS-IS System ID of the neighbor for the IS-IS SRv6 LAN End.X SID TLV and 4 octets of OSPFv3 Router-id of the neighbor for the OSPFv3 SRv6 LAN End.X SID TLV. o SID: 16 octet field. This field encodes the advertised SRv6 SID as 128 bit value. o Sub-TLVs : They are allocated from the IANA "BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs" registry and are used to advertise sub-TLVs that provide additional attributes for the specific SRv6 SID. This document defines one inSection 8. 4.3. SRv6 Link MSD Types The Link MSD TLV [RFC8814] of the BGP-LS Attribute of the Link NLRI is also used to advertise the limits and the SRH operations supported on the specific link by the SRv6 capable node. The SRv6 MSD Types specified in section 4 of[I-D.ietf-lsr-isis-srv6-extensions] are also used with the BGP-LS Link MSD TLV as these codepoints are shared between IS-IS, OSPF, and BGP-LS protocols. The description and semantics of these new MSD types for BGP-LS are identical as specified in [I-D.ietf-lsr-isis-srv6-extensions]. Each MSD type is encoded as a one-octet type followed by a one-octet value as specified in [RFC8814]. 5. SRv6 Prefix Attributes SRv6 attributes with an IPv6 prefix are advertised using the BGP-LS Attribute TLVs defined in this section and associated with the BGP-LS Prefix NLRI. 5.1. SRv6 Locator TLV As specified in [RFC8986], an SRv6 SID comprises Locator, Function and Argument parts. A node is provisioned with one or more locators supported by that node. Locators are covering prefixes for the set of SIDs provisioned Dawra, et al. Expires May 14, 2022 [Page 10] Internet-Draft BGP-LS Extensions for SRv6 November 2021 on that node. These Locators are advertised as BGP-LS Prefix NLRI objects along with the SRv6 Locator TLV in its BGP-LS Attribute. The IPv6 Prefix matching the Locator MAY be also advertised as a prefix reachability by the underlying routing protocol. In this case, the Prefix NLRI would be also associated with the Prefix Metric TLV that carries the routing metric for this prefix. When the Locator prefix is not being advertised as a prefix reachability, then the Prefix NLRI would have the SRv6 Locator TLV associated with it but no Prefix Metric TLV. In the absence of Prefix Metric TLV, the consumer of the BGP-LS topology information MUST NOT interpret the Locator prefix as a prefix reachability routing advertisement in the IGPs default SPF computation. The SRv6 Locator TLV 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Algorithm | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-TLVs (variable) . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: SRv6 Locator TLV Format Where: Type: 1162 Length: variable Flags: 1 octet of flags. The flags are derived from the SRv6 Locator TLV of IS-IS (section 7.1 of [I-D.ietf-lsr-isis-srv6-extensions]) and OSPFv3 (section 6.1 of [I-D.ietf-lsr-ospfv3-srv6-extensions]). Algorithm: 1 octet field. Algorithm associated with the SID. Algorithm values are defined in the IANA IGP Algorithm Type registry (https://www.iana.org/assignments/igp-parameters/igp- parameters.xhtml). Dawra, et al. Expires May 14, 2022 [Page 11] Internet-Draft BGP-LS Extensions for SRv6 November 2021 Reserved: 2 octet field. The value MUST be set to 0 and ignored on receipt. Metric: 4 octet field. The value of the metric for the Locator. Sub-TLVs : They are allocated from the IANA "BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs" registry and are used to advertise sub-TLVs that provide additional attributes for the given SRv6 Locator. Currently none are defined. 6. SRv6 SID NLRI SRv6 SID information is advertised in BGP UPDATE messages using the MP_REACH_NLRI and MP_UNREACH_NLRI attributes [RFC4760]. The "Link- State NLRI" defined in [RFC7752] is extended to carry the SRv6 SID information. A new "Link-State NLRI Type" is defined for SRv6 SID information as following: o Link-State NLRI Type: SRv6 SID NLRI (value 6). The format of this new NLRI type is as shown in the following figure: 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 +-+-+-+-+-+-+-+-+ | Protocol-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Identifier | | (8 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Local Node Descriptors (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SRv6 SID Descriptors (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5: SRv6 SID NLRI Format Where: o Protocol-ID: 1 octet field that specifies the protocol component through which BGP-LS learns the SRv6 SIDs of the node. The BGP-LS Protocol-ID registry was created by [RFC7752] and then additional assignments were made for other BGP-LS extensions. Dawra, et al. Expires May 14, 2022 [Page 12] Internet-Draft BGP-LS Extensions for SRv6 November 2021 o Identifier: 8 octet value as defined in [RFC7752]. o Local Node Descriptors TLV: as defined in [RFC7752] for IGPs, local and static configuration and as defined in [RFC9086] for BGP protocol. o SRv6 SID Descriptors: MUST include a single SRv6 SID Information TLV defined in Section 6.1 and optionally MAY include the Multi- Topology Identifier TLV as defined in [RFC7752]. New TLVs for advertisement within the BGP Link State Attribute [RFC7752] are defined in Section 7 to carry the attributes of an SRv6 SID. 6.1. SRv6 SID Information TLV An SRv6 SID is encoded using the SRv6 SID Information TLV. The TLV 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (16 octets) ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont ...) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont ...) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont ...) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 6: SRv6 SID Information TLV Format Where: Type: 518 Length: 16. SID: 16 octet field. This field encodes the advertised SRv6 SID as 128 bit value. Dawra, et al. Expires May 14, 2022 [Page 13] Internet-Draft BGP-LS Extensions for SRv6 November 2021 7. SRv6 SID Attributes This section specifies the TLVs to be carried in the BGP Link State Attribute associated with the BGP-LS SRv6 SID NLRI. 7.1. SRv6 Endpoint Behavior TLV Each SRv6 SID instantiated on an SRv6 capable node has specific instructions (called behavior) bound to it. [RFC8986] describes how behaviors are bound to a SID and also defines the initial set of well-known behaviors. The SRv6 Endpoint Behavior TLV is a mandatory TLV that MUST be included in the BGP-LS Attribute associated with the BGP-LS SRv6 SID NLRI. The TLV 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Endpoint Behavior | Flags | Algorithm | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 7: SRv6 Endpoint Behavior TLV Where: Type: 1250 Length: 4. Endpoint Behavior: 2 octet field. The Endpoint Behavior code point for this SRv6 SID as defined in section 10.2 of [RFC8986]. Flags: 1 octet of flags with the none defined currently. Reserved for future use and MUST be set to 0 and ignored on receipt. Algorithm: 1 octet field. Algorithm associated with the SID. Algorithm values are defined in the IGP Algorithm Type registry (https://www.iana.org/assignments/igp-parameters/igp- parameters.xhtml). Dawra, et al. Expires May 14, 2022 [Page 14] Internet-Draft BGP-LS Extensions for SRv6 November 2021 7.2. SRv6 BGP Peer Node SID TLV The BGP Peer Node SID and Peer Set SID for SR-MPLS are specified in [RFC9086]. Similar Peer Node and Peer Set functionality can be realized with SRv6 using SIDs with END.X behavior. The SRv6 BGP Peer Node SID TLV is a mandatory TLV for use in the BGP-LS Attribute for an SRv6 SID NLRI advertised by BGP for the EPE functionality. This TLV MUST be included along with SRv6 SIDs that are associated with the BGP Peer Node or Peer Set functionality. The TLV 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Weight | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Peer AS Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Peer BGP Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 8: SRv6 BGP Peer Node SID TLV Format Where: o Type: 1251 o Length: 12 o Flags: 1 octet of flags with the following definition (also refer to Section 9.3 for IANA registry): 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |B|S|P| Reserved| +-+-+-+-+-+-+-+-+ Figure 9: SRv6 BGP EPE SID Flags Format * B-Flag: Backup Flag. If set, the SID is eligible for protection (e.g. using IPFRR) as described in [RFC8355]. Dawra, et al. Expires May 14, 2022 [Page 15] Internet-Draft BGP-LS Extensions for SRv6 November 2021 * S-Flag: Set Flag. When set, the S-Flag indicates that the SID refers to a set of BGP peering sessions (i.e. BGP Peer Set SID functionality) and therefore MAY be assigned to one or more End.X SIDs associated with BGP peer sessions. * P-Flag: Persistent Flag: When set, the P-Flag indicates that the SID is persistently allocated, i.e., the value remains consistent across router restart and/or session flap. * Other bits are reserved for future use and MUST be set to 0 and ignored on receipt. o Weight: 1 octet field. The value represents the weight of the SID for the purpose of load balancing. The use of the weight is defined in [RFC8402]. o Reserved: 2 octet field. The value MUST be set to 0 and ignored on receipt. o Peer AS Number : 4 octets of BGP AS number of the peer router. o Peer BGP Identifier : 4 octets of the BGP Identifier (BGP Router- ID) of the peer router. For an SRv6 BGP EPE Peer Node SID, one instance of this TLV is associated with the SRv6 SID. For SRv6 BGP EPE Peer Set SID, multiple instances of this TLV (one for each peer in the "peer set") are associated with the SRv6 SID and the S (set/group) flag is SET. 8. SRv6 SID Structure TLV The SRv6 SID Structure TLV is used to advertise the length of each individual part of the SRv6 SID as defined in [RFC8986]. It is an optional TLV for use in the BGP-LS Attribute for an SRv6 SID NLRI and as a sub-TLV of the SRv6 End.X, IS-IS SRv6 LAN End.X and OSPFv3 SRv6 LAN End.X TLVs. The TLV 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LB Length | LN Length | Fun. Length | Arg. Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 10: SRv6 SID Structure TLV Dawra, et al. Expires May 14, 2022 [Page 16] Internet-Draft BGP-LS Extensions for SRv6 November 2021 Where: Type: 1252 Length: 4 Locator Block Length: 1 octet field. SRv6 SID Locator Block length in bits. Locator Node Length: 1 octet field. SRv6 SID Locator Node length in bits. Function Length: 1 octet field. SRv6 SID Function length in bits. Argument Length: 1 octet field. SRv6 SID Argument length in bits. The total of the locator block, locator node, function, and argument lengths MUST be less than or equal to 128. 9. IANA Considerations This document requests assigning code-points from the IANA "Border Gateway Protocol - Link State (BGP-LS) Parameters" registry as described in the sub-sections below. 9.1. BGP-LS NLRI-Types The following codepoints are assigned by IANA via the early allocation process from within the sub-registry called "BGP-LS NLRI- Types": +------+----------------------------+---------------+ | Type | NLRI Type | Reference | +------+----------------------------+---------------+ | 6 | SRv6 SID | this document | +------+----------------------------+---------------+ Figure 11: SRv6 SID NLRI Type Codepoint 9.2. BGP-LS TLVs The following TLV codepoints are assigned by IANA via the early allocation process from within the sub-registry called "BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs": Dawra, et al. Expires May 14, 2022 [Page 17] Internet-Draft BGP-LS Extensions for SRv6 November 2021 +----------+----------------------------------------+---------------+ | TLV Code | Description | Value defined | | Point | | in | +----------+----------------------------------------+---------------+ | 518 | SRv6 SID Information TLV | this document | | 1038 | SRv6 Capabilities TLV | this document | | 1106 | SRv6 End.X SID TLV | this document | | 1107 | IS-IS SRv6 LAN End.X SID TLV | this document | | 1108 | OSPFv3 SRv6 LAN End.X SID TLV | this document | | 1162 | SRv6 Locator TLV | this document | | 1250 | SRv6 Endpoint Behavior TLV | this document | | 1251 | SRv6 BGP Peer Node SID TLV | this document | | 1252 | SRv6 SID Structure TLV | this document | +----------+----------------------------------------+---------------+ Figure 12: SRv6 BGP-LS Attribute TLV Codepoints 9.3. SRv6 BGP EPE SID Flags This document requests the creation of a new registry called "SRv6 BGP EPE SID Flags" under the "Border Gateway Protocol - Link State (BGP-LS) Parameters" registry. The allocation policy of this registry is "Standards Action" according to [RFC8126]. The following flags are defined: Bit Description Reference --------------------------------------------------- 0 Backup Flag (B-Flag) This document 1 Set Flag (S-Flag) This document 2 Persistent Flag (P-Flag) This document 3-7 Unassigned 10. Manageability Considerations This section is structured as recommended in [RFC5706]. The new protocol extensions introduced in this document augment the existing IGP topology information that is distributed via [RFC7752]. Procedures and protocol extensions defined in this document do not affect the BGP protocol operations and management other than as discussed in the Manageability Considerations section of [RFC7752]. Specifically, the malformed attribute tests for syntactic checks in the Fault Management section of [RFC7752] now encompass the new BGP- LS extensions defined in this document. The semantic or content checking for the TLVs specified in this document and their association with the BGP-LS NLRI types or their BGP-LS Attribute is Dawra, et al. Expires May 14, 2022 [Page 18] Internet-Draft BGP-LS Extensions for SRv6 November 2021 left to the consumer of the BGP-LS information (e.g., an application or a controller) and not the BGP protocol. A consumer of the BGP-LS information retrieves this information over a BGP-LS session (refer Section 1 and 2 of [RFC7752]). The handling of semantic or content errors by the consumer would be dictated by the nature of its application usage and hence is beyond the scope of this document. The SR information introduced in BGP-LS by this specification may be used by BGP-LS consumer applications like an SR path computation engine (PCE) to learn the SRv6 capabilities of the nodes in the topology and the mapping of SRv6 segments to those nodes. This can enable the SR PCE to perform path computations based on SR for traffic engineering use-cases and to steer traffic on paths different from the underlying IGP based distributed best path computation. Errors in the encoding or decoding of the SRv6 information may result in the unavailability of such information to the SR PCE or incorrect information being made available to it. This may result in the SR PCE not being able to perform the desired SR-based optimization functionality or to perform it in an unexpected or inconsistent manner. The handling of such errors by applications like SR PCE may be implementation-specific and out of the scope of this document. The manageability considerations related to BGP EPE functionality are discussed in [RFC9086] in the context of SR-MPLS and they also apply to this document in the context of SRv6. The extensions, specified in this document, do not introduce any new configuration or monitoring aspects in BGP or BGP-LS other than as discussed in [RFC7752]. The manageability aspects of the underlying SRv6 features are covered by [I-D.ietf-spring-srv6-yang]. 11. Security Considerations The new protocol extensions introduced in this document augment the existing IGP topology information that is distributed via [RFC7752]. The advertisement of the SRv6 link-state information defined in this document presents a similar risk as associated with the existing set of link-state information as described in [RFC7752]. The Security Considerations section of [RFC7752] also applies to these extensions. The procedures and new TLVs defined in this document, by themselves, do not affect the BGP-LS security model discussed in [RFC7752]. The extensions introduced in this document are used to propagate IGP defined information ([I-D.ietf-lsr-isis-srv6-extensions] and [I-D.ietf-lsr-ospfv3-srv6-extensions]). These extensions represent the advertisement of SRv6 information associated with the IGP node, Dawra, et al. Expires May 14, 2022 [Page 19] Internet-Draft BGP-LS Extensions for SRv6 November 2021 link, and prefix. The IGP instances originating these TLVs are assumed to support all the required security and authentication mechanisms (as described in [I-D.ietf-lsr-isis-srv6-extensions] and [I-D.ietf-lsr-ospfv3-srv6-extensions]) in order to prevent any security issue when propagating the information into BGP-LS. The security considerations related to BGP EPE functionality are discussed in [RFC9086] in the context of SR-MPLS and they also apply to this document in the context of SRv6. BGP-LS SRv6 extensions enable traffic engineering use-cases within the Segment Routing domain. SR operates within a trusted domain [RFC8402] and its security considerations also apply to BGP-LS sessions when carrying SR information. The SR traffic engineering policies using the SIDs advertised via BGP-LS are expected to be used entirely within this trusted SR domain (e.g., between multiple AS or IGP domains within a single provider network). Therefore, precaution is necessary to ensure that the link-state information (including SRv6 information) advertised via BGP-LS sessions is limited to consumers in a secure manner within this trusted SR domain. BGP peering sessions for address-families other than Link-State may be set up to routers outside the SR domain. The isolation of BGP-LS peering sessions is recommended to ensure that BGP-LS topology information (including the newly added SR information) is not advertised to an external BGP peering session outside the SR domain. 12. Contributors James Uttaro AT&T USA Email: ju1738@att.com Hani Elmalky Ericsson USA Email: hani.elmalky@gmail.com Arjun Sreekantiah Individual USA Email: arjunhrs@gmail.com Les Ginsberg Cisco Systems USA Email: ginsberg@cisco.com Dawra, et al. Expires May 14, 2022 [Page 20] Internet-Draft BGP-LS Extensions for SRv6 November 2021 Shunwan Zhuang Huawei China Email: zhuangshunwan@huawei.com 13. Acknowledgements The authors would like to thank Peter Psenak, Arun Babu, Pablo Camarillo, Francois Clad, Peng Shaofu, Cheng Li, Dhruv Dhody, Tom Petch, and Dan Romascanu for their review of this document and their comments. The authors would also like to thanks Susan Hares for her shepherd review and Adrian Farrel for his detailed Routing Directorate review. 14. References 14.1. Normative References [I-D.ietf-lsr-isis-srv6-extensions] Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and Z. Hu, "IS-IS Extensions to Support Segment Routing over IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-18 (work in progress), October 2021. [I-D.ietf-lsr-ospfv3-srv6-extensions] Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak, "OSPFv3 Extensions for SRv6", draft-ietf-lsr- ospfv3-srv6-extensions-02 (work in progress), February 2021. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and S. Ray, "North-Bound Distribution of Link-State and Traffic Engineering (TE) Information Using BGP", RFC 7752, DOI 10.17487/RFC7752, March 2016, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . Dawra, et al. Expires May 14, 2022 [Page 21] Internet-Draft BGP-LS Extensions for SRv6 November 2021 [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, . [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, . [RFC8814] Tantsura, J., Chunduri, U., Talaulikar, K., Mirsky, G., and N. Triantafillis, "Signaling Maximum SID Depth (MSD) Using the Border Gateway Protocol - Link State", RFC 8814, DOI 10.17487/RFC8814, August 2020, . [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, . [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, . 14.2. Informative References [I-D.ietf-spring-srv6-yang] Raza, K., Agarwal, S., Liu, X., Hu, Z., Hussain, I., Shah, H., Voyer, D., Matsushima, S., Horiba, K., AbdelSalam, A., and J. Rajamanickam, "YANG Data Model for SRv6 Base and Static", draft-ietf-spring-srv6-yang-00 (work in progress), September 2020. [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, "Multiprotocol Extensions for BGP-4", RFC 4760, DOI 10.17487/RFC4760, January 2007, . Dawra, et al. Expires May 14, 2022 [Page 22] Internet-Draft BGP-LS Extensions for SRv6 November 2021 [RFC5706] Harrington, D., "Guidelines for Considering Operations and Management of New Protocols and Protocol Extensions", RFC 5706, DOI 10.17487/RFC5706, November 2009, . [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, . [RFC8355] Filsfils, C., Ed., Previdi, S., Ed., Decraene, B., and R. Shakir, "Resiliency Use Cases in Source Packet Routing in Networking (SPRING) Networks", RFC 8355, DOI 10.17487/RFC8355, March 2018, . Appendix A. Differences with BGP-EPE for SR-MPLS The signaling of SRv6 SIDs corresponding to BGP-EPE functionality as defined in this document differ from the signaling of SR-MPLS BGP-EPE SIDs as specified in [RFC9086]. This section provides a high-level overview of the same. There is no difference in the advertisement of the BGP Peer Adjacency SID in both SR-MPLS and SRv6 and it is advertised as an attribute of the Link NLRI which identifies a specific Layer 3 interface on the BGP Speaker. The difference is in the advertisement of the BGP Peer Node and Peer Set SIDs. In case of SR-MPLS, an additional Link NLRI is required to be advertised corresponding to each BGP Peering session on the node. Note that, this is not the same Link NLRI associated with the actual layer 3 interface even when the peering is setup using the interface IP addresses. These BGP-LS Link NLRIs are not really links in the traditional link-state routing data model but instead identify BGP peering sessions. The BGP Peer Node and/or Peer Set SIDs associated with that peering session are advertised as attributes associated with this peering Link NLRI. In the case of SRv6, each BGP Peer Node or Peer Set SID is considered to be associated with the BGP Speaker node and is advertised using the BGP-LS SRv6 SID NLRI while the peering session information is advertised as attributes associated with it. The advertisement of the BGP Peer Set SID for SR-MPLS is done by including that SID as an attribute in all the Link NLRIs corresponding to the peering sessions that are part of the "set". The advertisement of the BGP Peer Set SID for SRv6 is advertised Dawra, et al. Expires May 14, 2022 [Page 23] Internet-Draft BGP-LS Extensions for SRv6 November 2021 using a single SRv6 SID NLRI and all the peers associated with that "set" are indicated as attributes associated with the NLRI. Authors' Addresses Gaurav Dawra LinkedIn USA Email: gdawra.ietf@gmail.com Clarence Filsfils Cisco Systems Belgium Email: cfilsfil@cisco.com Ketan Talaulikar (editor) Cisco Systems India Email: ketant.ietf@gmail.com Mach Chen Huawei China Email: mach.chen@huawei.com Daniel Bernier Bell Canada Canada Email: daniel.bernier@bell.ca Bruno Decraene Orange France Email: bruno.decraene@orange.com Dawra, et al. Expires May 14, 2022 [Page 24]