]> Applying BGP-LS Segment Routing over IPv6(SRv6) Extensions to BGP-LS-SPF Huawei Technologies
No. 156 Beiqing Road Beijing China zhangli344@huawei.com
Huawei Technologies
No. 156 Beiqing Road Beijing China jie.dong@huawei.com
Routing LSVR Internet-Draft For network scenarios such as Massively Scaled Data Centers (MSDCs), BGP is extended for Link-State (LS) distribution and the Shortest Path First (SPF) algorithm based calculation. BGP-LS-SPF leverages the mechanisms of both BGP protocol and BGP-LS protocol extensions. Segment Routing over IPv6 (SRv6) provides a source routing mechanism that allows a flow to be restricted to a specific topological path, while maintaining per-flow state only at the ingress node(s) to the SRv6 domain. In some networks, it may be useful to enable SRv6 based source routing mechanism together with BGP-LS-SPF. This document proposes to introduce the BGP Link-State (BGP-LS) extensions for SRv6 to the BGP-LS-SPF SAFI.
Introduction extends BGP for Link-State (LS) distribution and the Shortest Path First (SPF) algorithm based calculation. BGP-LS-SPF leverages the mechanisms of both BGP protocol and BGP-LS protocol extensions , with the extensions to BGP-LS attribute and new NLRI selection rules. 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". SRv6 provides a mechanism that allows a flow to be restricted to a specific topological path, while maintaining per-flow state only at the ingress node(s) to the SRv6 domain. In network scenarios such as Data Center networks, WAN networks or other networks where BGP-LS-SPF can be used as the underlay routing protocol, it may be useful to enable SRv6 based source routing mechanism for traffic engineering and optimization. This document proposes to introduce the BGP Link-State (BGP-LS) extensions for SRv6 to the BGP-LS-SPF SAFI, and discusses which SRv6 extensions can be applied to BGP-LS-SPF SAFI.
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 when, and only when, they appear in all capitals, as shown here.
SRv6 Node Attribute TLVs Based on , the following SRv6 Node Attributes TLV SHOULD be supported in BGP-LS-SPF. Node Attribute TLVs for SRv6 with BGP-LS-SPF
Type Description Reference
1138 SRv6 Capabilities TLV RFC 9514
266 Node MSD TLV RFC 8814
1035 SR Algorithm TLV RFC 9085
SRv6 Capabilities TLV The SRv6 Capabilities TLV defined in 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. For BGP-LS-SPF, it SHOULD support this TLV to announce the SRv6 capabilities of BGP-LS-SPF nodes. A single instance of this TLV MUST be included in the BGP-SPF Node Attribute for each SRv6-capable node. defines the value of this TLV is copied from the ISIS SRv6 Capabilities sub-TLV or from the OSPFv3 SRv6 Capabilities TLV, but both of them have the same flag definition, therefore, the flags format of SRv6 Capabilities TLV of BGP-LS-SPF is consistent with that in ISIS SRv6 Capabilities sub-TLV and OSPFv3 SRv6 Capabilities TLV.
SRv6 Node MSD Types The Node MSD TLV defined in is used to advertise the limits and the Segment Routing Header (SRH) operations supported by the SRv6-capable node. For BGP-LS-SPF, it SHOULD support this TLV to advertise the limits and operations supported by BGP-LS-SPF node to enable segment routing. The SRv6 MSD types specified in are also used with the BGP-LS-SPF Node MSD TLV. The SRv6 Node MSD TLV is an optional TLV, for a specific MSD type, if the advertised value is zero or no value is advertised, then the headend can apply an SR Policy that only contains one segment without inserting any SRH header.
SR-Algorithm TLV specifies that the algorithm support for SRv6 is advertised via the SR-Algorithm TLV specified in . The SR-Algorithm is used to advertise the SR algorithms supported by the node. This TLV is a basic TLV of SR and SHOULD be supported in BGP-LS-SPF. The format of Algorithm fields in this TLV is consistent with that in ISIS, as defined in . The SR-Algorithm TLV is an optional TLV, when the originating router does not advertise the SR-Algorithm TLV, it implies that algorithm 0 is the only algorithm supported by the router.
SRv6 Link Attribute TLVs Based on and , the following Link Attributes SHOULD be supported in BGP-LS-SPF. Link Attribute TLVs for SRv6 with BGP-LS-SPF
Type Description Reference
1106 SRv6 End.X SID TLV RFC 9514
1106 L2 Bundle Member Attributes TLV RFC 9085
267 SRv6 Link MSD TLV RFC 8814
SRv6 End.X SID TLV The SRv6 End.X SID TLV defined in 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 the IS-IS or OSPFv3 protocols. It 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 . BGP-LS-SPF SHOULD support this TLV to advertise the SRv6 SIDs correspond to a point-to-point or adjacency of the node running the BGP-LS-SPF.
L2 Bundele Member Attributes TLV The L2 Bundle Member Attributes TLV is defined in , it identifies an L2 Bundle Member link, which in turn is associated with a parent L3 link. The TLV MAY include sub-TLVs that describe attributes associated with the bundle member. The network deployed BGP-LS-SPF may include trunk links. Therefore, BGP-LS-SPF MAY support this TLV to advertise L2 bundle member link attributes.
SRv6 Link MSD Types The Link MSD TLV defined in is used to advertise the limits and the SRH operations supported on the specific link by the SRv6-capable node. BGP-LS-SPF SHOULD support this TLV to advertise the limits and operations supported on the specific link to enable segment routing. The SRv6 MSD types specified in are also used with the BGP-LS-SPF Link MSD TLV. The SRv6 Link MSD TLV is an optional TLV, for a specific MSD type, if the advertised value is zero or no value is advertised, then the headend can apply an SR Policy that only contains one segment without inserting any SRH header.
SRv6 Prefix Attribute TLVs Based on , the BGP-LS SRv6 Prefix Attributes only includes the SRv6 Locator TLV. This TLV SHOULD be supported by BGP-LS-SPF. Prefix Attribute TLVs for SRv6 with BGP-LS-SPF
Type Description Reference
1162 SRv6 Locator TLV RFC 9514
SRv6 Locator TLV The SRv6 Locator TLV defined in is used to advertise the locators supported by each node. Each locator is advertised in a SRv6 Locator TLV. Locator is the key component of SRv6 SID, BGP-LS-SPF SHOULD support this TLV to enable segment routing. The flags fields of this TLV in BGP-LS-SPF is not used and MUST be set to zero on transmission and MUST be ignored on receipt.
SRv6 SID NLRI The SRv6 SID NLRI defined in is used to carry the SRv6 SID information. When SRv6 SIDs need to be advertised in BGP-SPF, the following NLRI type and attributes TLV for SRv6 SID SHOULD be supported in BGP-LS-SPF SAFI: SRv6 SID NLRI with BGP-LS-SPF
Type NLRI Type Reference
6 SRv6 SID NLRI RFC 9514
518 SRv6 SID Information TLV RFC 9514
1250 SRv6 Endpoint Behavior TLV RFC 9514
1252 SRv6 SID Structure TLV RFC 9514
The format of local node descriptors in this NLRI is consistent with BGP-LS local node descriptors , which MAY contain the Autonomous System and BGP-LS Identifier sub-TLV.
SRv6 SID Information TLV The SRv6 SID Information TLV is used to carry the SRv6 SID associated with a node in a SRv6 SID NLRI. This TLV SHOULD be supported in BGP-LS-SPF to advertise SRv6 SIDs.
SRv6 Endpoint Behavior TLV The Endpoint Behavior TLV defined in is a mandatory TLV included in the BGP-LS Attribute, used to advertise the behaviors associated with a SID. The BGP-LS-SPF SHOULD support this TLV to enable advertisement of behaviors associated with a SRv6 SID.
SRv6 SID Structure TLV The SRv6 SID Structure TLV defined in is used to advertise the length of each individual part of the SRv6 SID as defined in . It is an optional TLV in the BGP-LS Attribute for SRv6 SID NLRI and a sub-TLV of the SRv6 End.X SID. BGP-LS-SPF MAY support this TLV to indicate the length of each individual part of the SRv6 SID of BGP-LS-SPF especially in some scenarios using compressed SID.
Operational Considerations TBD
Security Considerations This document introduces no additional security vulnerabilities in addition to the ones as described in .
IANA Considerations
Acknowledgements TBD
References Normative References BGP Link-State Shortest Path First (SPF) Routing Arrcus, Inc. LabN Consulting, LLC LinkedIn Nokia Many Massively Scaled Data Centers (MSDCs) have converged on simplified L3 (Layer 3) routing. Furthermore, requirements for operational simplicity has led many of these MSDCs to converge on BGP as their single routing protocol for both their fabric routing and their Data Center Interconnect (DCI) routing. This document describes extensions to BGP to use BGP Link-State distribution and the Shortest Path First (SPF) algorithm. In doing this, it allows BGP to be efficiently used as both the underlay protocol and the overlay protocol in MSDCs. A Border Gateway Protocol 4 (BGP-4) This document discusses the Border Gateway Protocol (BGP), which is an inter-Autonomous System routing protocol. The primary function of a BGP speaking system is to exchange network reachability information with other BGP systems. This network reachability information includes information on the list of Autonomous Systems (ASes) that reachability information traverses. This information is sufficient for constructing a graph of AS connectivity for this reachability from which routing loops may be pruned, and, at the AS level, some policy decisions may be enforced. BGP-4 provides a set of mechanisms for supporting Classless Inter-Domain Routing (CIDR). These mechanisms include support for advertising a set of destinations as an IP prefix, and eliminating the concept of network "class" within BGP. BGP-4 also introduces mechanisms that allow aggregation of routes, including aggregation of AS paths. This document obsoletes RFC 1771. [STANDARDS-TRACK] Distribution of Link-State and Traffic Engineering Information Using BGP In many environments, a component external to a network is called upon to perform computations based on the network topology and the current state of the connections within the network, including Traffic Engineering (TE) information. This is information typically distributed by IGP routing protocols within the network. This document describes a mechanism by which link-state and TE information can be collected from networks and shared with external components using the BGP routing protocol. This is achieved using a BGP Network Layer Reachability Information (NLRI) encoding format. The mechanism applies to physical and virtual (e.g., tunnel) IGP links. The mechanism described is subject to policy control. Applications of this technique include Application-Layer Traffic Optimization (ALTO) servers and Path Computation Elements (PCEs). This document obsoletes RFC 7752 by completely replacing that document. It makes some small changes and clarifications to the previous specification. This document also obsoletes RFC 9029 by incorporating the updates that it made to RFC 7752. Key words for use in RFCs to Indicate Requirement Levels In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Border Gateway Protocol - Link State (BGP-LS) Extensions for Segment Routing over IPv6 (SRv6) 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, which is defined in RFC 9085. Signaling Maximum SID Depth (MSD) Using the Border Gateway Protocol - Link State This document defines a way for a Border Gateway Protocol - Link State (BGP-LS) speaker to advertise multiple types of supported Maximum SID Depths (MSDs) at node and/or link granularity. Such advertisements allow entities (e.g., centralized controllers) to determine whether a particular Segment Identifier (SID) stack can be supported in a given network. IS-IS Extensions to Support Segment Routing over the IPv6 Data Plane The Segment Routing (SR) architecture allows a flexible definition of the end-to-end path by encoding it as a sequence of topological elements called "segments". It can be implemented over the MPLS or the IPv6 data plane. This document describes the IS-IS extensions required to support SR over the IPv6 data plane. This document updates RFC 7370 by modifying an existing registry. Border Gateway Protocol - Link State (BGP-LS) Extensions for Segment Routing Segment Routing (SR) allows for a flexible definition of end-to-end paths by encoding paths as sequences of topological subpaths, called "segments". These segments are advertised by routing protocols, e.g., by the link-state routing protocols (IS-IS, OSPFv2, and OSPFv3) within IGP topologies. This document defines extensions to the Border Gateway Protocol - Link State (BGP-LS) address family in order to carry SR information via BGP. Informative References IS-IS Extensions for Segment Routing Segment Routing (SR) allows for a flexible definition of end-to-end paths within IGP topologies by encoding paths as sequences of topological sub-paths, called "segments". These segments are advertised by the link-state routing protocols (IS-IS and OSPF). This document describes the IS-IS extensions that need to be introduced for Segment Routing operating on an MPLS data plane. Border Gateway Protocol - Link State (BGP-LS) Extensions for Segment Routing BGP Egress Peer Engineering A node steers a packet through a controlled set of instructions, called segments, by prepending the packet with a list of segment identifiers (SIDs). A segment can represent any instruction, topological or service based. SR segments allow steering a flow through any topological path and service chain while maintaining per-flow state only at the ingress node of the SR domain. This document describes an extension to Border Gateway Protocol - Link State (BGP-LS) for advertisement of BGP Peering Segments along with their BGP peering node information so that efficient BGP Egress Peer Engineering (EPE) policies and strategies can be computed based on Segment Routing. Segment Routing over IPv6 (SRv6) Network Programming The Segment Routing over IPv6 (SRv6) Network Programming framework enables a network operator or an application to specify a packet processing program by encoding a sequence of instructions in the IPv6 packet header. Each instruction is implemented on one or several nodes in the network and identified by an SRv6 Segment Identifier in the packet. This document defines the SRv6 Network Programming concept and specifies the base set of SRv6 behaviors that enables the creation of interoperable overlays with underlay optimization.