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Network Working Group                                           K. Patel
Internet-Draft                                                 A. Lindem
Intended status: Standards Track                                  A. Roy
Expires: January 9, 2017                                        D. Yeung
                                                            V. Venugopal
                                                           Cisco Systems
                                                            July 8, 2016


           Shortest Path Routing Extensions for BGP Protocol
                   draft-keyupate-idr-bgp-spf-00.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
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on January 9, 2017.

Copyright Notice

   Copyright (c) 2016 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
   (http://trustee.ietf.org/license-info) in effect on the date of



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   publication of this document.  Please review these documents
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   than English.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  BGP Peering Models  . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  BGP Single-Hop Peering on Network Node Connections  . . .   4
     2.2.  BGP Peering Between Directly Connected Network Nodes  . .   4
     2.3.  BGP Peering in Route-Reflector or Controller Topology . .   4
   3.  Extensions to BGP-LS  . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Node NLRI Usage and Modifications . . . . . . . . . . . .   5
     3.2.  Link NLRI Usage . . . . . . . . . . . . . . . . . . . . .   6
     3.3.  Prefix NLRI Usage . . . . . . . . . . . . . . . . . . . .   6
   4.  Shortest Path Routing (SPF) Capability  . . . . . . . . . . .   6
   5.  Decision Process with SPF Algorithm . . . . . . . . . . . . .   6
     5.1.  Impact on BGP Tie-breaking attributes . . . . . . . . . .   7
     5.2.  Dual Stack Support  . . . . . . . . . . . . . . . . . . .   7
     5.3.  NEXT_HOP Manipulation . . . . . . . . . . . . . . . . . .   7
     5.4.  Error Handling  . . . . . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
     7.1.  Acknowledgements  . . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     8.2.  Information References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10







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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
   [I-D.ietf-rtgwg-bgp-routing-large-dc].  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 a NLRI carried
   within BGP-LS AFIs and BGP-LS SAFIs.  The BGP-LS extensions defined
   in [RFC7752] makes use of the Decision Process defined in [RFC4271].

   This draft modifies [RFC7752] by replacing its use of the existing
   Decision Process; in particular 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.

   Support for Multiple Topology Routing (MTR) as described in [RFC4915]
   is an area for further study dependent on deployment requirements.






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1.1.  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 3.2.

2.1.  BGP Single-Hop Peering on Network Node Connections

   The simplest peering model is the one described in section 5.2.1 of
   [I-D.ietf-rtgwg-bgp-routing-large-dc].  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, the Link-State address family capability has been
   exchanged, and the SPF capability has been exchanged 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 address
   family capability has been exchanged, the SPF capability has been
   exchanged, 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




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   BGP SPF, Link NLRI is advertised as long as the corresponding link is
   up and considered operational.

3.  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.

3.1.  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
   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).



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3.2.  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.

3.3.  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
   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.  Shortest Path Routing (SPF) Capability

   In order to replace the Phase 1 and 2 decision functions of the
   existing Decision Process with an SPF-based Decision Process, this
   draft introduces a new capability to signal the support of an SPF
   Decision Process.  The SPF Capability is a new BGP Capability
   [RFC5492].  The Capability Code for this capability is allocated by
   IANA as specified in the Section 6.  The Capability Length field of
   this capability has a value of 0.

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



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   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.

   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.  These selected Node NLRI and their Link/
   Prefix NLRI are use 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 it is no longer
   based on the output of the previous phases.  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.  Hence,
   for each valid NLRI, the Phase 3 decision function will simply need
   to advertise a valid NLRI instance dependent on policy.

5.1.  Impact on BGP Tie-breaking attributes

   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 in any
   received BGP Update messages.

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.



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   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.  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 new capability for BGP known as a SPF
   Capability.  We request IANA to assign a BGP capability number from
   BGP Capability Codes Registry.

   This document also defines a new attribute TLV for BGP LS Node NLRI.
   We request IANA to assign a new TLV for the SPF capability 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







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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.

8.  References

8.1.  Normative References

   [I-D.ietf-idr-bgpls-segment-routing-epe]
              Previdi, S., Filsfils, C., Ray, S., Patel, K., Dong, J.,
              and M. Chen, "Segment Routing BGP Egress Peer Engineering
              BGP-LS Extensions", draft-ietf-idr-bgpls-segment-routing-
              epe-05 (work in progress), May 2016.

   [I-D.ietf-rtgwg-bgp-routing-large-dc]
              Lapukhov, P., Premji, A., and J. Mitchell, "Use of BGP for
              routing in large-scale data centers", draft-ietf-rtgwg-
              bgp-routing-large-dc-11 (work in progress), June 2016.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

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

   [RFC5492]  Scudder, J. and R. Chandra, "Capabilities Advertisement
              with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
              2009, <http://www.rfc-editor.org/info/rfc5492>.

   [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,
              <http://www.rfc-editor.org/info/rfc7606>.

   [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,
              <http://www.rfc-editor.org/info/rfc7752>.



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8.2.  Information References

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

   [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,
              <http://www.rfc-editor.org/info/rfc4456>.

   [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,
              <http://www.rfc-editor.org/info/rfc4724>.

   [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, <http://www.rfc-editor.org/info/rfc4750>.

   [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,
              <http://www.rfc-editor.org/info/rfc4915>.

   [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,
              <http://www.rfc-editor.org/info/rfc5286>.

   [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,
              <http://www.rfc-editor.org/info/rfc5549>.

Authors' Addresses

   Keyur Patel
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   USA

   Email: keyupate@cisco.com






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   Acee Lindem
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   USA

   Email: acee@cisco.com


   Abhay Roy
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   USA

   Email: akr@cisco.com


   Derek Yeung
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   USA

   Email: myeung@cisco.com


   Venu Venugopal
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   USA

   Email: venuv@cisco.com

















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