]> Applying BGP-LS Segment Routing 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 IDR 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 (SR) 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 SR domain. In some networks, it may be useful to enable SR based source routing mechanism together with BGP-LS SPF. This document proposes to introduce the BGP Link-State (BGP-LS) extensions for segment routing to the BGP-LS SPF SAFI.
Introduction 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 , with the extensions to BGP-LS attribute and new NLRI selection rules defined in . Segment Routing (SR) leverages the source routing paradigm. A node steers a packet through an ordered list of instructions, called "segments". SR 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 SR domain. SR can be applied to the MPLS architecture (SR-MPLS) as defined in , and can also be applied to the IPv6 architecture (SRv6) as defined in and . In networks where BGP-LS-SPF is used as the underlay routing protocol, it may be useful to enable SR based source routing mechanism for traffic engineering and optimization. This document proposes to introduce the BGP Link-State (BGP-LS) extensions for segment routing to the BGP-LS-SPF SAFI. Both the extensions for SR-MPLS and SRv6 are specified. In general, most of the BGP-LS extensions for SR can be applied to BGP-LS SPF SAFI, only a few extensions are not applicable to BGP-LS SPF. For accuracy and documentation, the following subsections list the BGP-LS SR extensions which are introduced to BGP-LS SPF.
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.
SR-MPLS TLVs applicable to BGP-LS SPF When SR-MPLS is enabled in BGP-LS SPF, The following TLVs SHOULD be supported.
SR-MPLS Node Attribute TLVs Node Attribute TLVs for SR-MPLS with BGP-LS SPF
Type Description Reference
1161 SID/Label RFC 9085
1034 SR Capabilities RFC 9085
1035 SR Algorithm RFC 9085
1036 SR Local Block RFC 9085
1037 SRMS Preference RFC 9085
SR-MPLS Link Attribute TLVs The following Link Attribute TLVs SHOULD be supported: Link Attribute TLVs for SR-MPLS with BGP-LS SPF
Type Description Reference
1099 Adjacency SID TLV RFC 9085
1172 L2 Bundle Member Attributes TLV RFC 9085
SR-MPLS Prefix Attribute TLVs Prefix Attribute TLVs for SR-MPLS with BGP-LS SPF
Type Description Reference
1158 Prefix-SID RFC 9085
1159 Range RFC 9085
1170 Prefix Attribute Flags RFC 9085
1171 Source Router Identifier RFC 9085
1174 Source OSPF Router-ID RFC 9085
SRv6 Extensions Applicable to BGP-LS SPF When SRv6 is enabled with BGP-LS SPF, The following extensions SHOULD be supported.
SRv6 Node Attribute TLVs The following Node Attribute TLVs SHOULD be supported for SRv6: Node Attribute TLVs for SRv6 with BGP-LS SPF
Type Description Reference
1138 SRv6 Capabilities TLV RFC 9514
266 Node MSD TLV RFC 8814
SRv6 Link Attribute TLVs The following Link Attribute TLVs SHOULD be supported for SRv6: Link Attribute TLVs for SRv6 with BGP-LS SPF
Type Description Reference
1106 SRv6 End.X SID TLV RFC 9514
SRv6 Prefix Attribute TLVs The following Prefix Attribute TLVs SHOULD be supported for SRv6: Prefix Attribute TLVs for SRv6 with BGP-LS SPF
Type Description Reference
1162 SRv6 Locator TLV RFC 9514
SRv6 SID NLRI When SRv6 SIDs need to be advertised in BGP-SPF, the NLRI type 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
SRv6 SID Information NLRI The SRv6 SID Information TLV SHOULD be carried in the SRv6 SID NLRI. SRv6 SID Information TLV with BGP-LS SPF
Type NLRI Type Reference
518 SRv6 SID Information TLV RFC 9514
SRv6 SID Attribute TLVs The following TLVs MAY be carried in the BGP-LS Attribute associated with the SRv6 SID NLRI: SRv6 SID Attribute TLVs with BGP-LS SPF
Type NLRI Type Reference
1250 SRv6 Endpoint Behavior TLV RFC 9514
1251 SRv6 PeerNode SID TLV RFC 9514
1252 SRv6 SID Structure TLV RFC 9514
Operational Considerations TBD
Security Considerations This document introduces no additional security vulnerabilities in addition to the ones as described in .
IANA Considerations
Acknowledgements The authors would like to thank XXX for the review and discussion of this document.
Normative References 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. 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 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. Segment Routing with the MPLS Data Plane Segment Routing (SR) leverages the source-routing paradigm. A node steers a packet through a controlled set of instructions, called segments, by prepending the packet with an SR header. In the MPLS data plane, the SR header is instantiated through a label stack. This document specifies the forwarding behavior to allow instantiating SR over the MPLS data plane (SR-MPLS). IPv6 Segment Routing Header (SRH) Segment Routing can be applied to the IPv6 data plane using a new type of Routing Extension Header called the Segment Routing Header (SRH). This document describes the SRH and how it is used by nodes that are Segment Routing (SR) capable. 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. 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.