Usage and Applicability of BGP Link-State Shortest Path Routing (BGP-SPF) in Data Centers
draft-ietf-lsvr-applicability-20

Network Working Group                                           K. Patel
Internet-Draft                                              Arrcus, Inc.
Intended status: Informational                                 A. Lindem
Expires: 10 July 2025                            LabN Consulting, L.L.C.
                                                                S. Zandi
                                                                G. Dawra
                                                                Linkedin
                                                                 J. Dong
                                                     Huawei Technologies
                                                          6 January 2025

 Usage and Applicability of BGP Link-State Shortest Path Routing (BGP-
                          SPF) in Data Centers
                    draft-ietf-lsvr-applicability-20

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

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   This Internet-Draft will expire on 10 July 2025.

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   Please review these documents carefully, as they describe your rights
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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 Requirements . . . . . . . . . . . . .   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 . . . . . . . . . . . . . . . . . . . . .  11
   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.

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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

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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 severely 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.

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   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 preference over other AFI/SAFIs.  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 switch availability.  With BGP-SPF, the underlay will
   converge faster due to changes to the decision process that will

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   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 switches 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 switch 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-LS
   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.

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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) switches) 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 switches 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
   switches (in data center fabrics there is normally a single layer-3
   connection anyway).  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 prefix
   advertisements using existing BGP policy.  In Spine/Leaf topologies,
   it is not necessary to advertise BGP-LS Prefix NLRI received by
   leaves northbound to the spine nodes.  An aggregate route or a
   default route could suffice.  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.

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                +--------+    +--------+             +--------+
    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 Requirements

   The basic requirement is to be able to 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 requirement, it is useful to have
   to following information relating to the BGP session:

   *  Autonomous System (AS) and BGP Identifier of a potential peer.
      The latter can be used for debugging and to decrease the
      likelihood of BGP session establishment collisions.

   *  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.

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   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.  A potential requirement would be
   to determine this dynamically.  One mechanism, without specifying all
   the details, might be for the ToR switches to be identified when
   installed and for the others switches in the fabric to determine
   their level based on the distance from the closest ToR switch.

   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 could also be used to
   establish a multi-hop session with one or more controllers by
   advertising connectivity to one or more controllers.  However, once
   the multi-hop session traverses multiple nodes, it is bordering a
   distance-vector routing protocol and possibly this is not a good
   requirement for the discovery protocol.

5.5.  BGP Peer Discovery

5.5.1.  BGP IPv6 Simplified Peering

   To conserve IPv4 address space and simplify operations, BGP-LS 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 BGP-
   LS SPF 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] and these IPv6 link-local addresses must then be
   advertised in the BGP-LS Link Descriptor IPv6 Address TLV (262)
   [RFC9552].

5.5.2.  BGP-LS SPF Topology Visibility for Management

   Irrespective of whether or not BGP-LS 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

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   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.

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 including aggregation and prefix filtering may be
   used in conjunction with the BGP-LS SPF SAFI.  When aggregation
   policy is used, BGP-LS SPF prefix NLRI will be originated for the
   aggregate prefix and BGP-LS SPF prefix NLRI for components will be
   filtered.  Additionally, link and node NLRI may be filtered and
   abstracted by the prefix NLRI.

   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

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   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.

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, and Eric Vyncke 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-41, 14
              December 2024, <https://datatracker.ietf.org/doc/html/
              draft-ietf-lsvr-bgp-spf-41>.

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,
              <https://standards.ieee.org/standard/802_1AX-2020.html>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <https://www.rfc-editor.org/info/rfc2328>.

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   [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,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              DOI 10.17487/RFC4760, January 2007,
              <https://www.rfc-editor.org/info/rfc4760>.

   [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,
              <https://www.rfc-editor.org/info/rfc4861>.

   [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,
              <https://www.rfc-editor.org/info/rfc4957>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

   [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,
              <https://www.rfc-editor.org/info/rfc5580>.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.

   [RFC7404]  Behringer, M. and E. Vyncke, "Using Only Link-Local
              Addressing inside an IPv6 Network", RFC 7404,
              DOI 10.17487/RFC7404, November 2014,
              <https://www.rfc-editor.org/info/rfc7404>.

   [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,
              <https://www.rfc-editor.org/info/rfc7938>.

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   [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,
              <https://www.rfc-editor.org/info/rfc8177>.

   [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,
              <https://www.rfc-editor.org/info/rfc8950>.

   [RFC9552]  Talaulikar, K., Ed., "Distribution of Link-State and
              Traffic Engineering Information Using BGP", RFC 9552,
              DOI 10.17487/RFC9552, December 2023,
              <https://www.rfc-editor.org/info/rfc9552>.

   [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,
              <https://www.rfc-editor.org/info/rfc9667>.

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

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   Gaurav Dawra
   Linkedin
   222 2nd Street
   San Francisco, CA 94105
   United States of America
   Email: gdawra@linkedin.com

   Jie Dong
   Huawei Technologies
   No. 156 Beiqing Road
   Beijing
   China
   Email: jie.dong@huawei.com

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