Network Working Group K. Patel Internet-Draft Arrcus, Inc. Intended status: Standards Track A. Lindem Expires: July 16, 2018 Cisco Systems S. Zandi Linkedin G. Van de Velde Nokia January 12, 2018 Shortest Path Routing Extensions for BGP Protocol draft-keyupate-idr-bgp-spf-04.txt Abstract Many Massively Scaled Data Centers (MSDCs) have converged on simplified layer 3 routing. Furthermore, requirements for operational simplicity have lead 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 a solution which leverages BGP Link-State distribution and the Shortest Path First algorithm similar to Internal Gateway Protocols (IGPs) such as OSPF. 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 http://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 July 16, 2018. Copyright Notice Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. Patel, et al. Expires July 16, 2018 [Page 1] Internet-Draft BGP Protocol SPF Extensions January 2018 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://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. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. BGP Shortest Path First (SPF) Motivation . . . . . . . . 4 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 5 2. BGP Peering Models . . . . . . . . . . . . . . . . . . . . . 5 2.1. BGP Single-Hop Peering on Network Node Connections . . . 5 2.2. BGP Peering Between Directly Connected Network Nodes . . 5 2.3. BGP Peering in Route-Reflector or Controller Topology . . 6 3. BGP-LS Shortest Path Routing (SPF) SAFI . . . . . . . . . . . 6 4. Extensions to BGP-LS . . . . . . . . . . . . . . . . . . . . 6 4.1. Node NLRI Usage and Modifications . . . . . . . . . . . . 6 4.2. Link NLRI Usage . . . . . . . . . . . . . . . . . . . . . 7 4.3. Prefix NLRI Usage . . . . . . . . . . . . . . . . . . . . 7 4.4. BGP-LS Attribute Sequence-Number TLV . . . . . . . . . . 8 5. Decision Process with SPF Algorithm . . . . . . . . . . . . . 9 5.1. Phase-1 BGP NLRI Selection . . . . . . . . . . . . . . . 9 5.2. Dual Stack Support . . . . . . . . . . . . . . . . . . . 10 5.3. NEXT_HOP Manipulation . . . . . . . . . . . . . . . . . . 10 5.4. NLRI Advertisement and Convergence . . . . . . . . . . . 10 5.5. Error Handling . . . . . . . . . . . . . . . . . . . . . 11 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 7.1. Acknowledgements . . . . . . . . . . . . . . . . . . . . 12 7.2. Contributorss . . . . . . . . . . . . . . . . . . . . . . 12 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 Patel, et al. Expires July 16, 2018 [Page 2] Internet-Draft BGP Protocol SPF Extensions January 2018 8.1. Normative References . . . . . . . . . . . . . . . . . . 12 8.2. Information References . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 1. Introduction Many Massively Scaled Data Centers (MSDCs) have converged on simplified layer 3 routing. Furthermore, requirements for operational simplicity have lead many of these MSDCs to converge on BGP [RFC4271] as their single routing protocol for both their fabric routing and their Data Center Interconnect (DCI) routing. Requirements and procedures for using BGP are described in [RFC7938]. This document describes an alternative solution which leverages BGP- LS [RFC7752] and the Shortest Path First algorithm similar to Internal Gateway Protocols (IGPs) such as OSPF [RFC2328]. [RFC4271] defines the Decision Process that is used to select routes for subsequent advertisement by applying the policies in the local Policy Information Base (PIB) to the routes stored in its Adj-RIBs- In. The output of the Decision Process is the set of routes that are announced by a BGP speaker to its peers. These selected routes are stored by a BGP speaker in the speaker's Adj-RIBs-Out according to policy. [RFC7752] describes a mechanism by which link-state and TE information can be collected from networks and shared with external components using BGP. This is achieved by defining NLRI carried within BGP-LS AFI and BGP-LS SAFIs. The BGP-LS extensions defined in [RFC7752] makes use of the Decision Process defined in [RFC4271]. This document augments [RFC7752] by replacing its use of the existing Decision Process. The BGP-LS-SPF and BGP-LS-SPF-VPN AFI/SAFI are introduced to insure backward compatibility. The Phase 1 and 2 decision functions of the Decision Process are replaced with the Shortest Path Algorithm (SPF) also known as the Dijkstra Algorithm. The Phase 3 decision function is also simplified since it is no longer dependent on the previous phases. This solution avails the benefits of both BGP and SPF-based IGPs. These include TCP based flow-control, no periodic link-state refresh, and completely incremental NLRI advertisement. These advantages can reduce the overhead in MSDCs where there is a high degree of Equal Cost Multi- Path (ECMPs) and the topology is very stable. Additionally, using a SPF-based computation can support fast convergence and the computation of Loop-Free Alternatives (LFAs) [RFC5286] in the event of link failures. Furthermore, a BGP based solution lends itself to multiple peering models including those incorporating route- reflectors [RFC4456] or controllers. Patel, et al. Expires July 16, 2018 [Page 3] Internet-Draft BGP Protocol SPF Extensions January 2018 Support for Multiple Topology Routing (MTR) as described in [RFC4915] is an area for further study dependent on deployment requirements. 1.1. BGP Shortest Path First (SPF) Motivation Given that [RFC7938] already describes how BGP could be used as the sole routing protocol in an MSDC, one might question the motivation for defining an alternate BGP deployment model when a mature solution exists. For both alternatives, BGP offers the operational benefits of a single routing protocol. However, BGP SPF offers some unique advantages above and beyond standard BGP distance-vector routing. A primary advantage is that all BGP speakers in the BGP SPF routing domain will have a complete view of the topology. This will allow support of ECMP, IP fast-reroute (e.g., Loop-Free Alternatives), Shared Risk Link Groups (SRLGs), and other routing enhancements without advertisement of addition BGP paths or other extensions. In short, the advantages of an IGP such as OSPF [RFC2328] are availed in BGP. With the simplified BGP decision process as defined in Section 5.1, NLRI changes can be disseminated throughout the BGP routing domain much more rapidly (equivalent to IGPs with the proper implementation). Another primary advantage is a potential reduction in NLRI advertisement. With standard BGP distance-vector routing, a single link failure may impact 100s or 1000s prefixes and result in the withdrawal or re-advertisement of the attendant NLRI. With BGP SPF, only the BGP speakers corresponding to the link NLRI need withdraw the corresponding BGP-LS Link NLRI. This advantage will contribute to both faster convergence and better scaling. With controller and route-reflector peering models, BGP SPF advertisement and distributed computation require a minimal number of sessions and copies of the NLRI since only the latest verion of the NLRI from the originator is required. Given that verification of the adjacencies is done outside of BGP (see Section 2), each BGP speaker will only need as many sessions and copies of the NLRI as required for redundancy (e.g., one for SPF computation and another for backup). Functions such as Optimized Route Reflection (ORR) are supported without extension by virture of the primary advantages. Additionally, a controller could inject topology that is learned outside the BGP routing domain. Given that controllers are already consuming BGP-LS NLRI [RFC7752], reusing for the BGP-LS SPF leverages the existing controller implementations. Patel, et al. Expires July 16, 2018 [Page 4] Internet-Draft BGP Protocol SPF Extensions January 2018 Another potential advantage of BGP SPF is that both IPv6 and IPv4 can be supported in the same address family using the same topology. Although not described in this version of the document, multi- topology extensions can be used to support separate IPv4, IPv6, unicast, and multicast topologies while sharing the same NLRI. Finally, the BGP SPF topology can be used as an underlay for other BGP address families (using the existing model) and realize all the above advantages. A simplified peering model using IPv6 link-local addresses as next-hops can be deployed similar to [RFC5549]. 1.2. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 2. BGP Peering Models Depending on the requirements, scaling, and capabilities of the BGP speakers, various peering models are supported. The only requirement is that all BGP speakers in the BGP SPF routing domain receive link- state NLRI on a timely basis, run an SPF calculation, and update their data plane appropriately. The content of the Link NLRI is described in Section 4.2. 2.1. BGP Single-Hop Peering on Network Node Connections The simplest peering model is the one described in section 5.2.1 of [RFC7938]. In this model, EBGP single-hop sessions are established over direct point-to-point links interconnecting the network nodes. For the purposes of BGP SPF, Link NLRI is only advertised if a single-hop BGP session has been established and the Link-State/SPF adddress family capability has been exchanged [RFC4790] on the corresponding session. If the session goes down, the NLRI will be withdrawn. 2.2. BGP Peering Between Directly Connected Network Nodes In this model, BGP speakers peer with all directly connected network nodes but the sessions may be multi-hop and the direct connection discovery and liveliness detection for those connections are independent of the BGP protocol. How this is accomplished is outside the scope of this document. Consequently, there will be a single session even if there are multiple direct connections between BGP speakers. For the purposes of BGP SPF, Link NLRI is advertised as long as a BGP session has been established, the Link-State/SPF Patel, et al. Expires July 16, 2018 [Page 5] Internet-Draft BGP Protocol SPF Extensions January 2018 address family capability has been exchanged [RFC4790] and the corresponding link is up and considered operational. 2.3. BGP Peering in Route-Reflector or Controller Topology In this model, BGP speakers peer solely with one or more Route Reflectors [RFC4456] or controllers. As in the previous model, direct connection discovery and liveliness detection for those connections are done outside the BGP protocol. For the purposes of BGP SPF, Link NLRI is advertised as long as the corresponding link is up and considered operational. 3. BGP-LS Shortest Path Routing (SPF) SAFI In order to replace the Phase 1 and 2 decision functions of the existing Decision Process with an SPF-based Decision Process and streamline the Phase 3 decision functions in a backward compatible manner, this draft introduces a couple AFI/SAFIs for BGP LS SPF operation. The BGP-LS-SPF (AF 16388 / SAFI TBD1) and BGP-LS-SPF-VPN (AFI 16388 / SAFI TBD2) [RFC4790] are allocated by IANA as specified in the Section 6. 4. Extensions to BGP-LS [RFC7752] describes a mechanism by which link-state and TE information can be collected from networks and shared with external components using BGP protocol. It contains two parts: definition of a new BGP NLRI that describes links, nodes, and prefixes comprising IGP link-state information and definition of a new BGP path attribute (BGP-LS attribute) that carries link, node, and prefix properties and attributes, such as the link and prefix metric or auxiliary Router- IDs of nodes, etc. The BGP protocol will be used in the Protocol-ID field specified in table 1 of [I-D.ietf-idr-bgpls-segment-routing-epe]. The local and remote node descriptors for all NLRI will be the BGP Router-ID (TLV 516) and either the AS Number (TLV 512) [RFC7752] or the BGP Confederation Member (TLV 517) [I-D.ietf-idr-bgpls-segment-routing-epe]. However, if the BGP Router-ID is known to be unique within the BGP Routing domain, it can be used as the sole descriptor. 4.1. Node NLRI Usage and Modifications The SPF capability is a new Node Attribute TLV that will be added to those defined in table 7 of [RFC7752]. The new attribute TLV will only be applicable when BGP is specified in the Node NLRI Protocol ID Patel, et al. Expires July 16, 2018 [Page 6] Internet-Draft BGP Protocol SPF Extensions January 2018 field. The TBD TLV type will be defined by IANA. The new Node Attribute TLV will contain a single octet SPF algorithm field: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SPF Algorithm | +-+-+-+-+-+-+-+-+ The SPF Algorithm may take the following values: 1 - Normal SPF 2 - Strict SPF When computing the SPF for a given BGP routing domain, only BGP nodes advertising the SPF capability attribute will be included the Shortest Path Tree (SPT). 4.2. Link NLRI Usage The criteria for advertisement of Link NLRI are discussed in Section 2. Link NLRI is advertised with local and remote node descriptors as described above and unique link identifiers dependent on the addressing. For IPv4 links, the links local IPv4 (TLV 259) and remote IPv4 (TLV 260) addresses will be used. For IPv6 links, the local IPv6 (TLV 261) and remote IPv6 (TLV 262) addresses will be used. For unnumbered links, the link local/remote identifiers (TLV 258) will be used. For links supporting having both IPv4 and IPv6 addresses, both sets of descriptors may be included in the same Link NLRI. The link identifiers are described in table 5 of [RFC7752]. The link IGP metric attribute TLV (TLV 1095) as well as any others required for non-SPF purposes SHOULD be advertised. Algorithms such as setting the metric inversely to the link speed as done in the OSPF MIB [RFC4750] may be supported. However, this is beyond the scope of this document. 4.3. Prefix NLRI Usage Prefix NLRI is advertised with a local descriptor as described above and the prefix and length used as the descriptors (TLV 265) as described in [RFC7752]. The prefix metric attribute TLV (TLV 1155) as well as any others required for non-SPF purposes SHOULD be Patel, et al. Expires July 16, 2018 [Page 7] Internet-Draft BGP Protocol SPF Extensions January 2018 advertised. For loopback prefixes, the metric should be 0. For non- loopback, the setting of the metric is beyond the scope of this document. 4.4. BGP-LS Attribute Sequence-Number TLV A new BGP-LS Attribute TLV to BGP-LS NLRI types is defined to assure the most recent version of a given NLRI is used in the SPF computation. The TBD TLV type will be defined by IANA. The new BGP- LS Attribute TLV will contain an 8 octet sequence number. The usage of the Sequence Number TLV is described in Section 5.1. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number (High-Order 32 Bits) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number (Low-Order 32 Bits) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Sequence Number The 64-bit strictly increasing sequence number is incremented for every version of BGP-LS NLRI originated. BGP speakers implementing this specification MUST use available mechanisms to preserve the sequence number's strictly increasing property for the deployed life of the BGP speaker (including cold restarts). One mechanism for accomplishing this would be to use the high-order 32 bits of the sequence number as a wrap/boot count that is incremented anytime the BGP Router router loses its sequence number state or the low-order 32 bits wrap. When incrementing the sequence number for each self-originated NLRI, the sequence number should be treated as an unsigned 64-bit value. If the lower-order 32-bit value wraps, the higher-order 32-bit value should be incremented and saved in non-volatile storage. If by some chance the BGP Speaker is deployed long enough that there is a possibility that the 64-bit sequence number may wrap or a BGP Speaker completely loses its sequence number state (e.g, the BGP speaker hardware is replaced), the phase 1 decision function (see Section 5.1) rules should insure convergance, albeit, not immediately. Patel, et al. Expires July 16, 2018 [Page 8] Internet-Draft BGP Protocol SPF Extensions January 2018 5. Decision Process with SPF Algorithm The Decision Process described in [RFC4271] takes place in three distinct phases. The Phase 1 decision function of the Decision Process is responsible for calculating the degree of preference for each route received from a Speaker's peer. The Phase 2 decision function is invoked on completion of the Phase 1 decision function and is responsible for choosing the best route out of all those available for each distinct destination, and for installing each chosen route into the Loc-RIB. The combination of the Phase 1 and 2 decision functions is also known as a Path vector algorithm. When BGP-LS-SPF NLRI is received, all that is required is to determine whether it is the best-path by examining the Node-ID and sequence number as described in Section 5.1. If the best-path NLRI had changed, it will be advertised to other BGP-LS-SPF peers. If the attributes have changed (other than the sequence number), a BGP SPF calculation will be scheduled. However, a changed best-path can be advertised to other peer immediately and propagation of changes can approach IGP convergence times. The SPF based Decision process starts with selecting only those Node NLRI whose SPF capability TLV matches with the local BGP speaker's SPF capability TLV value. Since Link-State NLRI always contains the local descriptor [RFC7752], it will only be originated by a single BGP speaker in the BGP routing domain. These selected Node NLRI and their Link/Prefix NLRI are used to build a directed graph during the SPF computation. The best paths for BGP prefixes are installed as a result of the SPF process. The Phase 3 decision function of the Decision Process [RFC4271] is also simplified since under normal SPF operation, a BGP speaker would advertise the NLRI selected for the SPF to all BGP peers with the BGP-LS/BGP-SPF AFI/SAFI. Application of policy would not be prevented but would normally not be necessary. 5.1. Phase-1 BGP NLRI Selection The rules for NLRI selection are greatly simplified from [RFC4271]. 1. If the NLRI is received from the BGP speaker originating the NLRI (as determined by the comparing BGP Router ID in the NLRI Node identifiers with the BGP speaker Router ID), then it is preferred over the same NLRI from non-originators. 2. If the Sequence-Number TLV is present in the BGP-LS Attribute, then the NLIR with the most recent, i.e., highest sequence number is selected. BGP-LS NLRI with a Sequence-Number TLV will be Patel, et al. Expires July 16, 2018 [Page 9] Internet-Draft BGP Protocol SPF Extensions January 2018 considered more recent than NLRI without a BGP-LS or a BGP-LS Attribute that doesn't include the Sequence-Number TLV. 3. The final tie-breaker is the NLRI from the BGP Speaker with the numerically largest BGP Router ID. The modified Decision Process with SPF algorithm uses the metric from Link and Prefix NLRI Attribute TLVs [RFC7752]. As a result, any attributes that would influence the Decision process defined in [RFC4271] like ORIGIN, MULTI_EXIT_DISC, and LOCAL_PREF attributes are ignored by the SPF algorithm. Furthermore, the NEXT_HOP attribute value is preserved and validated but otherwise ignored during the SPF or best-path. 5.2. Dual Stack Support The SPF based decision process operates on Node, Link, and Prefix NLRIs that support both IPv4 and IPv6 addresses. Whether to run a single SPF instance or multiple SPF instances for separate AFs is a matter of a local implementation. Normally, IPv4 next-hops are calculated for IPv4 prefixes and IPv6 next-hops are calculated for IPv6 prefixes. However, an interesting use-case is deployment of [RFC5549] where IPv6 link-local next-hops are calculated for both IPv4 and IPv6 prefixes. As stated in Section 1, support for Multiple Topology Routing (MTR) is an area for future study. 5.3. NEXT_HOP Manipulation A BGP speaker that supports SPF extensions MAY interact with peers that don't support SPF extensions. If the BGP Link-State address family is advertised to a peer not supporting the SPF extensions described herein, then the BGP speaker MUST conform to the NEXT_HOP rules mentioned in [RFC4271] when announcing the Link-State address family routes to those peers. All BGP peers that support SPF extensions would locally compute the NEXT_HOP values as result of the SPF process. As a result, the NEXT_HOP attribute is always ignored on receipt. However BGP speakers should set the NEXT_HOP address according to the NEXT_HOP attribute rules mentioned in [RFC4271]. 5.4. NLRI Advertisement and Convergence A local failure will prevent a link from being used in the SPF calculation due to the IGP bi-directional connectivity requirment. Consequently, local link failues should always be given priority over updates (e.g., withdrawing all routes learned on a session) in order to ensure the highest priority progation and optimal convergence. Patel, et al. Expires July 16, 2018 [Page 10] Internet-Draft BGP Protocol SPF Extensions January 2018 Delaying the withdrawal of non-local routes is an area for further study as more IGP-like mechanisms would be required to prevent usage of stale NLRI. 5.5. Error Handling When a BGP speaker receives a BGP Update containing a malformed SPF Capability TLV in the Node NLRI BGP-LS Attribute [RFC7752], it MUST ignore the received TLV and the Node NLRI and not pass it to other BGP peers as specified in [RFC7606]. When discarding a Node NLRI with malformed TLV, a BGP speaker SHOULD log an error for further analysis. 6. IANA Considerations This document defines a couple AFI/SAFIs for BGP LS SPF operation and requests IANA to assign the BGP-LS-SPF AFI 16388 / SAFI TBD1 and the BGP-LS-SPF-VPN AFI 16388 / SAFI TBD2 as described in [RFC4750]. This document also defines two attribute TLV for BGP LS NLRI. We request IANA to assign TLVs for the SPF capability and the Sequence Number from the "BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs" Registry. Additionally, IANA is requested to create a new registry for "BGP-LS SPF Capability Algorithms" for the value of the algorithm both in the BGP-LS Node Attribute TLV and the BGP SPF Capability. The initial assignments are: +-------------+-----------------------------------+ | Value(s) | Assignment Policy | +-------------+-----------------------------------+ | 0 | Reserved (not to be assigned) | | | | | 1 | SPF | | | | | 2 | Strict SPF | | | | | 3-254 | Unassigned (IETF Review) | | | | | 255 | Reserved (not to be assigned) | +-------------+-----------------------------------+ BGP-LS SPF Capability Algorithms Patel, et al. Expires July 16, 2018 [Page 11] Internet-Draft BGP Protocol SPF Extensions January 2018 7. Security Considerations This extension to BGP does not change the underlying security issues inherent in the existing [RFC4724] and [RFC4271]. 7.1. Acknowledgements The authors would like to thank .... for the review and comments. 7.2. Contributorss In addition to the authors listed on the front page, the following co-authors have contributed to the document. Derek Yeung Arrcus, Inc. derek@arrcus.com Abhay Roy Cisco Systems akr@cisco.com Venu Venugopal Cisco Systems venuv@cisco.com 8. References 8.1. Normative References [I-D.ietf-idr-bgpls-segment-routing-epe] Previdi, S., Filsfils, C., Patel, K., Ray, S., and J. Dong, "BGP-LS extensions for Segment Routing BGP Egress Peer Engineering", draft-ietf-idr-bgpls-segment-routing- epe-14 (work in progress), December 2017. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [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, . Patel, et al. Expires July 16, 2018 [Page 12] Internet-Draft BGP Protocol SPF Extensions January 2018 [RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K. Patel, "Revised Error Handling for BGP UPDATE Messages", RFC 7606, DOI 10.17487/RFC7606, August 2015, . [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, . [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, . 8.2. Information References [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, DOI 10.17487/RFC2328, April 1998, . [RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route Reflection: An Alternative to Full Mesh Internal BGP (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006, . [RFC4724] Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y. Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724, DOI 10.17487/RFC4724, January 2007, . [RFC4750] Joyal, D., Ed., Galecki, P., Ed., Giacalone, S., Ed., Coltun, R., and F. Baker, "OSPF Version 2 Management Information Base", RFC 4750, DOI 10.17487/RFC4750, December 2006, . [RFC4790] Newman, C., Duerst, M., and A. Gulbrandsen, "Internet Application Protocol Collation Registry", RFC 4790, DOI 10.17487/RFC4790, March 2007, . [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", RFC 4915, DOI 10.17487/RFC4915, June 2007, . Patel, et al. Expires July 16, 2018 [Page 13] Internet-Draft BGP Protocol SPF Extensions January 2018 [RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for IP Fast Reroute: Loop-Free Alternates", RFC 5286, DOI 10.17487/RFC5286, September 2008, . [RFC5549] Le Faucheur, F. and E. Rosen, "Advertising IPv4 Network Layer Reachability Information with an IPv6 Next Hop", RFC 5549, DOI 10.17487/RFC5549, May 2009, . Authors' Addresses Keyur Patel Arrcus, Inc. Email: keyur@arrcus.com Acee Lindem Cisco Systems 301 Midenhall Way Cary, NC 27513 USA Email: acee@cisco.com Shawn Zandi Linkedin 222 2nd Street San Francisco, CA 94105 USA Email: szandi@linkedin.com Gunter Van de Velde Nokia Antwerp Belgium Email: gunter.van_de_velde@nokia.com Patel, et al. Expires July 16, 2018 [Page 14]