Network Working Group K. Patel Internet-Draft Arrcus, Inc. Intended status: Informational A. Lindem Expires: 27 July 2025 LabN Consulting, L.L.C. S. Zandi G. Dawra Linkedin J. Dong Huawei Technologies 23 January 2025 Usage and Applicability of BGP Link-State Shortest Path Routing (BGP- SPF) in Data Centers draft-ietf-lsvr-applicability-22 Abstract This document discusses the usage and applicability of BGP Link-State Shortest Path First (BGP-SPF) extensions in data center networks utilizing Clos or Fat-Tree topologies. The document is intended to provide simplified guidance for the deployment of BGP-SPF extensions. 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 27 July 2025. Copyright Notice Copyright (c) 2025 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. Patel, et al. Expires 27 July 2025 [Page 1] Internet-Draft BGP-SPF Applicability January 2025 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Recommended Reading . . . . . . . . . . . . . . . . . . . . . 3 3. Common Deployment Scenario . . . . . . . . . . . . . . . . . 3 4. Justification for BGP-SPF Extension . . . . . . . . . . . . . 4 5. BGP-SPF Applicability to Clos Networks . . . . . . . . . . . 4 5.1. Usage of BGP-LS SPF SAFI . . . . . . . . . . . . . . . . 5 5.1.1. Relationship to Other BGP AFI/SAFI Tuples . . . . . . 5 5.2. Peering Models . . . . . . . . . . . . . . . . . . . . . 5 5.2.1. Sparse Peering Model . . . . . . . . . . . . . . . . 6 5.2.2. Bi-Connected Graph Heuristic . . . . . . . . . . . . 7 5.3. BGP Spine/Leaf Topology Policy . . . . . . . . . . . . . 7 5.4. BGP Peer Discovery Considerations . . . . . . . . . . . . 8 5.5. BGP Peer Discovery . . . . . . . . . . . . . . . . . . . 9 5.5.1. BGP IPv6 Simplified Peering . . . . . . . . . . . . . 9 5.5.2. BGP-LS SPF Topology Visibility for Management . . . . 9 5.5.3. Data Center Interconnect (DCI) Applicability . . . . 10 6. Non-CLOS/FAT Tree Topology Applicability . . . . . . . . . . 10 7. Non-Transit Node Capability . . . . . . . . . . . . . . . . . 10 8. BGP Policy Applicability . . . . . . . . . . . . . . . . . . 10 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 10. Security Considerations . . . . . . . . . . . . . . . . . . . 11 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 12.1. Normative References . . . . . . . . . . . . . . . . . . 11 12.2. Informative References . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 1. Introduction This document complements [I-D.ietf-lsvr-bgp-spf] by discussing the applicability of the BGP-SPF technology in a simple and fairly common deployment scenario, which is described in Section 3. Section 4 describes the reasons for BGP modifications for such deployments. Section 5 covers the BGP Link-State Shortest Path First (IGP-SPF) protocol enhancements to BGP to meet these requirements and their applicability to data center [Clos] networks. Patel, et al. Expires 27 July 2025 [Page 2] Internet-Draft BGP-SPF Applicability January 2025 2. Recommended Reading This document assumes knowledge of existing data center networks and data center network topologies [Clos]. This document also assumes knowledge of data center routing protocols such as BGP [RFC4271], BGP-SPF [I-D.ietf-lsvr-bgp-spf], OSPF [RFC2328] [RFC5340], as well as data center Operations, Administration, and Maintenance (OAM) protocols like Link Layer Discovery Protocol (LLDP) [RFC4957] and Bi- Directional Forwarding Detection (BFD) [RFC5580]. 3. Common Deployment Scenario Within a data center, servers are commonly interconnected using the Clos topology [Clos]. The Clos topology is fully non-blocking and the topology is realized using Equal Cost Multi-Path (ECMP). In a multi-stage Clos topology, the minimum number of parallel paths in each tier is determined by the width of the stage as shown in the figure 1. Tier 1 +-----+ |NODE | +->| 1 |--+ | +-----+ | Tier 2 | | Tier 2 +-----+ | +-----+ | +-----+ +------------->|NODE |--+->|NODE |--+--|NODE |--------------+ | +-----| 5 |--+ | 2 | +--| 7 |-----+ | | | +-----+ +-----+ +-----+ | | | | | | | | +-----+ +-----+ +-----+ | | | +------+---->|NODE |--+ |NODE | +--|NODE |-----+------+ | | | | +---| 6 |--+->| 3 |--+--| 8 |---+ | | | | | | | +-----+ | +-----+ | +-----+ | | | | | |Tier 3| | | | | |Tier 3| | +-----+ +-----+ | +-----+ | +-----+ +-----+ |NODE | |NODE | +->|NODE |--+ |NODE | |NODE | | 9 | | 10 | | 4 | | 11 | | 12 | +-----+ +-----+ +-----+ +-----+ +-----+ | | | | | | | | | | | | <- Servers -> <- Servers -> Tier 1 is comprised of Nodes 1, 2, 3, and 4 Tier 2 is comprised of Nodes 5, 6, 7, and 8 Tier 3 is comprised of Nodes 9, 10, 11, and 12 Figure 1: Illustration of the basic Clos Patel, et al. Expires 27 July 2025 [Page 3] Internet-Draft BGP-SPF Applicability January 2025 4. Justification for BGP-SPF Extension To simplify L3 routing and operations, many data centers use BGP as a routing protocol to create both an underlay and an overlay network for their Clos Topologies [RFC7938]. However, BGP is a path-vector routing protocol. Since it does not create a fabric topology, it uses hop-by-hop External BGP (EBGP) peering to facilitate hop-by-hop routing to create the underlay network and to resolve any overlay next hops. The hop-by-hop BGP peering paradigm imposes several restrictions within a Clos. It prohibits the deployment of Route Reflectors/Route Controllers as the EBGP sessions are congruent with the data path. The BGP best-path algorithm is prefix-based and it prevents announcements of prefixes to other BGP speakers until the best-path decision process has been performed for the prefix at each intermediate hop. These restrictions significantly delay the overall convergence of the underlay network within a Clos network. The BGP-SPF modifications allow BGP to overcome these limitations. Furthermore, using the BGP-LS Network Layer Reachability Information (NLRI) format allows the BGP-SPF data to be advertised for nodes, links, and prefixes in the BGP routing domain and used for Short- Path-First (SPF) computations [RFC9552]. Additional motivation for deploying BGP-SPF is included in [I-D.ietf-lsvr-bgp-spf]. 5. BGP-SPF Applicability to Clos Networks With the BGP-SPF extensions [I-D.ietf-lsvr-bgp-spf], the BGP best- path computation and route computation are replaced with link-state algorithms such as those used by OSPF [RFC2328], both to determine whether an BGP-LS-SPF NLRI has changed and needs to be re-advertised and to compute the BGP routes. These modifications will significantly improve convergence of the underlay while affording the operational benefits of a single routing protocol [RFC7938]. Data center controllers typically require visibility to the BGP topology to compute traffic-engineered paths. These controllers learn the topology and other relevant information via the BGP-LS address family [RFC9552] which is totally independent of the underlay address families (usually IPv4/IPv6 unicast). Furthermore, in traditional BGP underlays, all the BGP routers will need to advertise their BGP-LS information independently. With the BGP-SPF extensions, controllers can learn the topology using the same BGP advertisements used to compute the underlay routes. Furthermore, these data center controllers can avail the convergence advantages of the BGP-SPF extensions. The placement of controllers can be outside of the forwarding path or within the forwarding path. Patel, et al. Expires 27 July 2025 [Page 4] Internet-Draft BGP-SPF Applicability January 2025 Alternatively, as each and every router in the BGP-SPF domain will have a complete view of the topology, the operator can also choose to configure BGP sessions in the hop-by-hop peering model described in [RFC7938] along with BFD [RFC5580]. In doing so, while the hop-by- hop peering model lacks the inherent benefits of the controller-based model, BGP updates need not be serialized by the BGP best-path algorithm in either of these models. This helps overall network convergence. 5.1. Usage of BGP-LS SPF SAFI Section 5.1 of [I-D.ietf-lsvr-bgp-spf] defines a new BGP-LS-SPF SAFI for announcement of the BGP-SPF link-state. The NLRI format and its associated attributes follow the format of BGP-LS for node, link, and prefix announcements. Whether the peering model within a Clos follows hop-by-hop peering described in [RFC7938] or any controller- based or route-reflector peering, an operator can exchange BGP-LS-SPF SAFI routes over the BGP peering by simply configuring BGP-LS-SPF SAFI between the necessary BGP speakers. The BGP-LS-SPF SAFI can also co-exist with BGP IP Unicast SAFI [RFC4760] which could exchange overlapping IP routes. One use case for this is where BGP-LS-SPF routes are used for the underlay and BGP IP Unicast routes for VPNs are advertised in the overlay as described in [RFC4364]. The routes received by these SAFIs are evaluated, stored, and announced independently according to the rules of [RFC4760]. The tie-breaking of route installation is a matter of the local policies and preferences of the network operator. Finally, as the BGP-SPF peering is done following the procedures described in [RFC4271], all the existing transport security mechanisms including [RFC5925] are available for the BGP-LS-SPF SAFI. 5.1.1. Relationship to Other BGP AFI/SAFI Tuples Normally, the BGP-LS-SPF AFI/SAFI is used solely to compute the underlay and is given precedence over other AFI/SAFIs in route processing. Other BGP SAFIs, e.g., IPv6/IPv6 Unicast VPN would use the BGP-SPF computed routes for next hop resolution. 5.2. Peering Models As previously stated, BGP-SPF can be deployed using the existing peering model where there is a single-hop BGP session on each and every link in the data center fabric [RFC7938]. This provides for both the advertisement of routes and the determination of link and neighboring router availability. With BGP-SPF, the underlay will converge faster due to changes to the decision process that will Patel, et al. Expires 27 July 2025 [Page 5] Internet-Draft BGP-SPF Applicability January 2025 allow NLRI changes to be advertised faster after detecting a change. 5.2.1. Sparse Peering Model Alternately, BFD [RFC5580] can be used to swiftly determine the availability of links and the BGP peering model can be significantly sparser than the data center fabric. BGP-SPF sessions only need to be established with enough peers to provide a bi-connected graph. If Internal BGP (IBGP) is used, then the BGP routers at tier N-1 will act as route-reflectors for the routers at tier N. The obvious usage of sparse peering is to avoid parallel BGP sessions on links between the same two routers in the data center fabric. However, this use case is not very useful since parallel L3 links between the same two BGP routers are rare in Clos or Fat-Tree topologies. Additionally, when there are multiple links, they are often aggregated at the link layer using Link Aggregation Groups (LAGs) [IEEE.802.1AX] rather than at the IP layer. Two more interesting scenarios are described below. In current data center topologies, there is often a very dense mesh of links between levels, e.g., leaf and spine, providing 32-way, 64-way, or more Equal-Cost Multi-Path (ECMP) paths. In these topologies, it is desirable not to have a BGP session on every link and techniques such as the one described in Section 5.2.2 can be used to establish sessions on some subset of northbound links. For example, in a Spine-Leaf topology, each leaf router would only peer with a subset of the spines dependent on the flooding redundancy required to be reasonably certain that every node within the BGP-SPF routing domain has the complete topology. Alternately, controller-based data center topologies are envisioned where BGP speakers within the data center only establish BGP sessions with two or more controllers. In these topologies, fabric nodes below the first tier, as shown in Figure 1 of [RFC7938], will establish BGP multi-hop sessions with the controllers. For the multi-hop sessions, determining the route to the controllers without depending on BGP would need to be through some other means beyond the scope of this document. However, the BGP discovery mechanisms described in Section 5.5 would be one possibility. Patel, et al. Expires 27 July 2025 [Page 6] Internet-Draft BGP-SPF Applicability January 2025 5.2.2. Bi-Connected Graph Heuristic With this heuristic, discovery of BGP SPF peers is assumed, e.g., as described in Section 5.5. In this context, "bi-connected" refers to the fact that there must be an adverised link NLRI for both BGP SPF peers associated with the link before the link can be used in the BGP SPF route calcuation. Additionally, it assumed that the direction of the peering can be ascertained. In the context of a data center fabric, the direction is either northbound (toward the spine), southbound (toward the Top-Of-Rack (ToR) routers) or east-west (same level in the hierarchy). The determination of the direction is beyond the scope of this document. However, it would be reasonable to assume a technique where the ToR routers can be identified and the number of hops to the ToR is used to determine the direction. In this heuristic, BGP speakers allow passive session establishment for southbound BGP sessions. For northbound sessions, BGP speakers will attempt to maintain two northbound BGP sessions with different routers. For east-west sessions, passive BGP session establishment is allowed. However, a BGP speaker will never actively establish an east-west BGP session unless it cannot establish two northbound BGP sessions. BGP SPF sparse peering deployments not using this hueristic are possible but are not described herein and are considered out of scope. 5.3. BGP Spine/Leaf Topology Policy One of the advantages of using BGP-SPF as the underlay protocol is that BGP policy can be applied at any level. For example, depending on the topology, it may be possible to aggregate or filter prefix advertisements using existing BGP policy. In Spine/Leaf topologies, it is not necessary to advertise BGP-LS Prefix NLRI received by leaf nodes from the spine back to other spine nodes. If a common AS is used for the spine nodes, this can easily be accomplished with EBGP and a simple policy to filter advertisements from the leaves to the spine if the first AS in the AS path is the spine AS. In the figure below, the leaves would not advertise any NLRI with AS 64512 as the first AS in the AS path. Patel, et al. Expires 27 July 2025 [Page 7] Internet-Draft BGP-SPF Applicability January 2025 +--------+ +--------+ +--------+ AS 64512 | | | | | | for Spine | Spine 1+----+ Spine 2+- ......... -+ Spine N| Nodes at | | | | | | this Level +-+-+-+-++ ++-+-+-+-+ +-+-+-+-++ +------+ | | | | | | | | | | | | +-----|-|-|------+ | | | | | | | | | +--|-|-|--------+-|-|-----------------+ | | | | | | | | | +---+ | | | | | | | | | | | | +--|-|-------------------+ | | | | | | | | | | | | +------+ +----+ | | | | | | | | | +--------------|----------+ | | | | | | | | | +-------------+ | | | | | | | | +----|--|----------------|--|--------+ | | | | | | +------|--|--------------+ | | | | | | | | +------+ | | | | | | | | ++--+--++ +-+-+--++ ++-+--+-+ ++-+--+-+ | Leaf 1| | Leaf 2| ........ | Leaf X| | Leaf Y| +-------+ +-------+ +-------+ +-------+ Figure 2: Spine/Leaf Topology Policy 5.4. BGP Peer Discovery Considerations The basic functionality of peer discovery is to be discover the address of a single-hop peer in case where the peer address is not pre-configured. This is being accomplished today by using IPv6 Router Advertisements (RA) [RFC4861] and assuming that a BGP session is desired with any discovered peer. Beyond the basic functionality, it may be useful to have the following information relating to the BGP session: * Autonomous System (AS) and BGP Identifier of a potential peer. * Security capabilities supported and for cryptographic authentication, the security capabilities and possibly a key-chain [RFC8177] to be used. * Session Policy Identifier - A group number or name used to associate common session parameters with the peer. For example, in a data center, BGP sessions with a ToR device could have different parameters than BGP sessions between leaf and spine. In a data center fabric, it is often useful to know whether a peer is southbound (towards the servers) or northbound (towards the spine or super-spine), e.g., Section 5.2.2. One mechanism, without specifying Patel, et al. Expires 27 July 2025 [Page 8] Internet-Draft BGP-SPF Applicability January 2025 all the details, might be for the ToR routers to be identified when installed and for the others routers in the fabric to determine their level based on the distance from the closest ToR router. If there are multiple links between BGP speakers or the links between BGP speakers are unnumbered, it is also useful to be able to establish multi-hop sessions using the loopback addresses. This will often require the discovery protocol to install route(s) toward the potential peer loopback addresses prior to BGP session establishment. Finally, a simple BGP discovery protocol may be used to establish a multi-hop session with one or more controllers by advertising connectivity to one or more controllers. 5.5. BGP Peer Discovery 5.5.1. BGP IPv6 Simplified Peering To conserve IPv4 address space and simplify operations, BGP-SPF routers in Clos/Fat Tree deployments can use IPv6 addresses as peer address. For IPv4 address families, IPv6 peering as specified in [RFC8950] can be deployed to avoid configuring IPv4 addresses on router interfaces. When this is done, dynamic discovery mechanisms, as described in Section 5.5, can be used to learn the global or link- local IPv6 peer addresses and IPv4 addresses need not be configured on these interfaces. If IPv6 link-local peering is used, then configuration of IPv6 global addresses is also not required [RFC7404] . The Link Local/Remote Identifiers of the peering interfaces MUST be used in the link NLRI as described in section 5.2.2 of [I-D.ietf-lsvr-bgp-spf]. 5.5.2. BGP-LS SPF Topology Visibility for Management Irrespective of whether or not BGP-SPF is used for route calculation, the BGP-LS-SPF route advertisements can be used to periodically construct the Clos/Fat Tree topology. This is especially useful in deployments where an Interior Gateway Protocol (IGP) is not used and the base BGP-LS routes [RFC9552] are not available. The resultant topology visibility can then be used for troubleshooting and consistency checking. This would normally be done on a central controller or other management tool which could also be used for fabric data path verification. The precise algorithms and heuristics, as well as the complete set of management applications is beyond the scope of this document. Patel, et al. Expires 27 July 2025 [Page 9] Internet-Draft BGP-SPF Applicability January 2025 5.5.3. Data Center Interconnect (DCI) Applicability Since BGP-SPF is to be used for the routing underlay and DCI gateway boxes typically have direct or very simple connectivity, BGP external sessions would typically not include the BGP-LS-SPF SAFI. 6. Non-CLOS/FAT Tree Topology Applicability The BGP-SPF extensions [I-D.ietf-lsvr-bgp-spf] can be used in other topologies and avail the inherent convergence improvements. Additionally, sparse peering techniques may be utilized Section 5.2. However, determining whether to establish a BGP session is more complex and the heuristic described in Section 5.2.2 cannot be used. In such topologies, other techniques such as those described in [RFC9667] may be employed. One potential deployment would be the underlay for a Service Provider (SP) backbone where usage of a single protocol, i.e., BGP, is desired. 7. Non-Transit Node Capability In certain scenarios, a BGP node wishes to participate in the BGP-SPF topology but never be used for transit traffic. These include situations where a server wants to make application services available to clients homed at subnets throughout the BGP-SPF domain but does not ever want to be used as a router (i.e., carry transit traffic). Another specific instance is where a controller is resident on a server and direct connectivity to the controller is required throughout the entire domain. This can readily be accomplished using the BGP-LS Node NLRI Attribute SPF Status TLV as described in [I-D.ietf-lsvr-bgp-spf]. 8. BGP Policy Applicability Existing BGP policy such as prefix filtering may be used in conjunction with the BGP-LS-SPF SAFI. When BGP policy is used with the BGP-LS-SPF SAFI, BGP speakers in the BGP-LS-SPF routing domain will not all have the same set of NLRI and will compute a different BGP local routing table. Consequently, care must be taken to assure routing is consistent and blackholes or routing loops do not ensue. However, this is no different than if traditional BGP routing using the IPv4 and IPv6 address families were used. 9. IANA Considerations No IANA updates are requested by this document. Patel, et al. Expires 27 July 2025 [Page 10] Internet-Draft BGP-SPF Applicability January 2025 10. Security Considerations This document introduces no new security considerations above and beyond those already specified in the [RFC4271] and [I-D.ietf-lsvr-bgp-spf]. 11. Acknowledgements The authors would like to thank Alvaro Retana, Yan Filyurin, Boris Hassanov, Stig Venaas, Ron Bonica, Mallory Knodel, Dhruv Dhody, Erik Kline, Eric Vyncke, and John Scudder for their review and comments. 12. References 12.1. Normative References [I-D.ietf-lsvr-bgp-spf] Patel, K., Lindem, A., Zandi, S., and W. Henderickx, "BGP Link-State Shortest Path First (SPF) Routing", Work in Progress, Internet-Draft, draft-ietf-lsvr-bgp-spf-51, 14 January 2025, . 12.2. Informative References [Clos] "A Study of Non-Blocking Switching Networks", The Bell System Technical Journal, Vol. 32(2), DOI 10.1002/j.1538-7305.1953.tb01433.x, March 1953. [IEEE.802.1AX] IEEE, "IEEE Standard for Local and Metropolitan Area Networks: Link Aggregation", IEEE Std 802.1AX-2020, 2020, . [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, DOI 10.17487/RFC2328, April 1998, . [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, . [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 2006, . Patel, et al. Expires 27 July 2025 [Page 11] Internet-Draft BGP-SPF Applicability January 2025 [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, "Multiprotocol Extensions for BGP-4", RFC 4760, DOI 10.17487/RFC4760, January 2007, . [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, DOI 10.17487/RFC4861, September 2007, . [RFC4957] Krishnan, S., Ed., Montavont, N., Njedjou, E., Veerepalli, S., and A. Yegin, Ed., "Link-Layer Event Notifications for Detecting Network Attachments", RFC 4957, DOI 10.17487/RFC4957, August 2007, . [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, . [RFC5580] Tschofenig, H., Ed., Adrangi, F., Jones, M., Lior, A., and B. Aboba, "Carrying Location Objects in RADIUS and Diameter", RFC 5580, DOI 10.17487/RFC5580, August 2009, . [RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP Authentication Option", RFC 5925, DOI 10.17487/RFC5925, June 2010, . [RFC7404] Behringer, M. and E. Vyncke, "Using Only Link-Local Addressing inside an IPv6 Network", RFC 7404, DOI 10.17487/RFC7404, November 2014, . [RFC7938] Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of BGP for Routing in Large-Scale Data Centers", RFC 7938, DOI 10.17487/RFC7938, August 2016, . [RFC8177] Lindem, A., Ed., Qu, Y., Yeung, D., Chen, I., and J. Zhang, "YANG Data Model for Key Chains", RFC 8177, DOI 10.17487/RFC8177, June 2017, . Patel, et al. Expires 27 July 2025 [Page 12] Internet-Draft BGP-SPF Applicability January 2025 [RFC8950] Litkowski, S., Agrawal, S., Ananthamurthy, K., and K. Patel, "Advertising IPv4 Network Layer Reachability Information (NLRI) with an IPv6 Next Hop", RFC 8950, DOI 10.17487/RFC8950, November 2020, . [RFC9552] Talaulikar, K., Ed., "Distribution of Link-State and Traffic Engineering Information Using BGP", RFC 9552, DOI 10.17487/RFC9552, December 2023, . [RFC9667] Li, T., Ed., Psenak, P., Ed., Chen, H., Jalil, L., and S. Dontula, "Dynamic Flooding on Dense Graphs", RFC 9667, DOI 10.17487/RFC9667, October 2024, . Authors' Addresses Keyur Patel Arrcus, Inc. 2077 Gateway Pl San Jose, CA, 95110 United States of America Email: keyur@arrcus.com Acee Lindem LabN Consulting, L.L.C. 301 Midenhall Way Cary, NC, 95110 United States of America Email: acee.ietf@gmail.com Shawn Zandi Linkedin 222 2nd Street San Francisco, CA 94105 United States of America Email: szandi@linkedin.com Gaurav Dawra Linkedin 222 2nd Street San Francisco, CA 94105 United States of America Email: gdawra@linkedin.com Patel, et al. Expires 27 July 2025 [Page 13] Internet-Draft BGP-SPF Applicability January 2025 Jie Dong Huawei Technologies No. 156 Beiqing Road Beijing China Email: jie.dong@huawei.com Patel, et al. Expires 27 July 2025 [Page 14]