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Versions: 00 01 02 03 04 05 draft-ietf-bess-datacenter-gateway

BESS Working Group                                              J. Drake
Internet-Draft                                                 A. Farrel
Intended status: Standards Track                                E. Rosen
Expires: January 2, 2018                                Juniper Networks
                                                                K. Patel
                                                            Arrcus, Inc.
                                                                L. Jalil
                                                                 Verizon
                                                            July 1, 2017


   Gateway Auto-Discovery and Route Advertisement for Segment Routing
                     Enabled Domain Interconnection
                 draft-drake-bess-datacenter-gateway-04

Abstract

   Data centers have become critical components of the infrastructure
   used by network operators to provide services to their customers.
   Data centers are attached to the Internet or a backbone network by
   gateway routers.  One data center typically has more than one gateway
   for commercial, load balancing, and resiliency reasons.

   Segment routing is a popular protocol mechanism for operating within
   a data center, but also for steering traffic that flows between two
   data center sites.  In order that one data center site may load
   balance the traffic it sends to another data center site it needs to
   know the complete set of gateway routers at the remote data center,
   the points of connection from those gateways to the backbone network,
   and the connectivity across the backbone network.

   Segment routing may also be operated in other domains, such as access
   networks.  Those domains also need to be connected across backbone
   networks through gateways.

   This document defines a mechanism using the BGP Tunnel Encapsulation
   attribute to allow each gateway router to advertise the routes to the
   prefixes in the segment routing domains to which it provides access,
   and also to advertise on behalf of each other gateway to the same
   segment routing domain.

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 [RFC2119].





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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
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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
   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 January 2, 2018.

Copyright Notice

   Copyright (c) 2017 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
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  SR Domain Gateway Auto-Discovery  . . . . . . . . . . . . . .   5
   3.  Relationship to BGP Link State and Egress Peer Engineering  .   6
   4.  Advertising an SR Domain Route Externally . . . . . . . . . .   6
   5.  Encapsulation . . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  Manageability Considerations  . . . . . . . . . . . . . . . .   7
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     10.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9




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1.  Introduction

   Data centers (DCs) have become critical components of the
   infrastructure used by network operators to provide services to their
   customers.  DCs are attached to the Internet or a backbone network by
   gateway routers (GWs).  One DC typically has more than one GW for
   various reasons including commercial preferences, load balancing, and
   resiliency against connection of device failure.

   Segment routing (SR) [I-D.ietf-spring-segment-routing] is a popular
   protocol mechanism for operating within a DC, but also for steering
   traffic that flows between two DC sites.  In order for an ingress DC
   that uses SR to load balance the flows it sends to an egress DC, it
   needs to know the complete set of entry nodes (i.e., GWs) for that
   egress DC from the backbone network connecting the two DCs.  Note
   that it is assumed that the connected set of DCs and the backbone
   network connecting them are part of the same SR BGP Link State (LS)
   instance ([RFC7752] and [I-D.ietf-idr-bgpls-segment-routing-epe]) so
   that traffic engineering using SR may be used for these flows.

   Segment routing may also be operated in other domains, such as access
   networks.  Those domains also need to be connected across backbone
   networks through gateways.

   Suppose that there are two gateways, GW1 and GW2 as shown in
   Figure 1, for a given egress segment routing domain and that they
   each advertise a route to prefix X which is located within the egress
   segment routing domain with each setting itself as next hop.  One
   might think that the GWs for X could be inferred from the routes'
   next hop fields, but typically it is not the case that both routes
   get distributed across the backbone: rather only the best route, as
   selected by BGP, is distributed.  This precludes load balancing flows
   across both GWs.


















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           -----------------                    ---------------------
          | Ingress         |                  | Egress     ------   |
          | SR Domain       |                  | SR Domain |Prefix|  |
          |                 |                  |           |   X  |  |
          |                 |                  |            ------   |
          |       --        |                  |   ---          ---  |
          |      |GW|       |                  |  |GW1|        |GW2| |
           -------++---------                   ----+-----------+-+--
                  | \                               |          /  |
                  |  \                              |         /   |
                  |  -+-------------        --------+--------+--  |
                  | ||PE|       ----|      |----   |PE|    |PE| | |
                  | | --       |ASBR+------+ASBR|   --      --  | |
                  | |           ----|      |----                | |
                  | |               |      |                    | |
                  | |           ----|      |----                | |
                  | | AS1      |ASBR+------+ASBR|           AS2 | |
                  | |           ----|      |----                | |
                  |  ---------------        --------------------  |
                --+-----------------------------------------------+--
               | |PE|                                           |PE| |
               |  --                 AS3                         --  |
               |                                                     |
                -----------------------------------------------------


         Figure 1: Example Segment Routing Domain Interconnection

   The obvious solution to this problem is to use the BGP feature that
   allows the advertisement of multiple paths in BGP (known as Add-
   Paths) [RFC7911] to ensure that all routes to X get advertised by
   BGP.  However, even if this is done, the identity of the GWs will be
   lost as soon as the routes get distributed through an Autonomous
   System Border Router (ASBR) that will set itself to be the next hop.
   And if there are multiple Autonomous Systems (ASes) in the backbone,
   not only will the next hop change several times, but the Add-Paths
   technique will experience scaling issues.  This all means that this
   approach is limited to SR domains connected over a single AS.

   This document defines a solution that overcomes this limitation and
   works equally well with a backbone constructed from one or more ASes.
   This solution uses the Tunnel Encapsulation attribute
   [I-D.ietf-idr-tunnel-encaps] as follows:

      We define a new tunnel type, "SR tunnel".  When the GWs to a given
      SR domain advertise a route to a prefix X within the SR domain,
      they will each include a Tunnel Encapsulation attribute with
      multiple tunnel instances each of type "SR tunnel", one for each



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      GW, and each containing a Remote Endpoint sub-TLV with that GW's
      address.

   In other words, each route advertised by any GW identifies all of the
   GWs to the same SR domain (see Section 2 for a discussion of how GWs
   discover each other).  Therefore, even if only one of the routes is
   distributed to other ASes, it will not matter how many times the next
   hop changes, as the Tunnel Encapsulation attribute (and its remote
   endpoint sub-TLVs) will remain unchanged.

   To put this in the context of Figure 1, GW1 and GW2 discover each
   other as gateways for the egress SR domain.  Both GW1 and GW2
   advertise themselves as having routes to prefix X.  Furthermore, GW1
   includes a Tunnel Encapsulation attribute with a tunnel instance of
   type "SR tunnel" for itself and another for GW2.  Similarly, GW2
   includes a Tunnel Encapsulation for itself and another for GW1.  The
   gateway in the ingress SR domain can now see all possible paths to
   the egress SR domain regardless of which route advertisement is
   propagated to it, and it can choose one or balance traffic flows as
   it sees fit.

2.  SR Domain Gateway Auto-Discovery

   To allow a given SR domain's GWs to auto-discover each other and to
   coordinate their operations, the following procedures are
   implemented:

   o  Each GW is configured with an identifier for the SR domain that is
      common across all GWs to the domain (i.e., across all GWs to all
      SR domains that are interconnected) and unique across all SR
      domains that are connected.

   o  A route target ([RFC4360]) is attached to each GW's auto-discovery
      route and has its value set to the SR domain identifier.

   o  Each GW constructs an import filtering rule to import any route
      that carries a route target with the same SR domain identifier
      that the GW itself uses.  This means that only these GWs will
      import those routes and that all GWs to the same SR domain will
      import each other's routes and will learn (auto-discover) the
      current set of active GWs for the SR domain.

   The auto-discovery route each GW advertises consists of the
   following:

   o  An IPv4 or IPv6 NLRI containing one of the GW's loopback addresses
      (that is, with AFI/SAFI that is one of 1/1, 2/1, 1/4, or 2/4).




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   o  A Tunnel Encapsulation attribute containing the GW's encapsulation
      information, which at a minimum consists of an SR tunnel TLV (type
      to be allocated by IANA) with a Remote Endpoint sub-TLV as
      specified in [I-D.ietf-idr-tunnel-encaps].

   To avoid the side effect of applying the Tunnel Encapsulation
   attribute to any packet that is addressed to the GW itself, the GW
   SHOULD use a different loopback address for the two cases.

   As described in Section 1, each GW will include a Tunnel
   Encapsulation attribute for each GW that is active for the SR domain
   (including itself), and will include these in every route advertised
   externally to the SR domain by each GW.  As the current set of
   active GWs changes (due to the addition of a new GW or the failure/
   removal of an existing GW) each externally advertised route will be
   re-advertised with the set of SR tunnel instances reflecting the
   current set of active GWs.

   If a gateway becomes disconnected from the backbone network, or if
   the SR domain operator decides to terminate the gateway's activity,
   it withdraws the advertisements described above.  This means that
   remote gateways at other sites will stop seeing advertisements from
   this gateway.  It also means that other local gateways at this site
   will "unlearn" the removed gateway and stop including a Tunnel
   Encapsulation attribute for the removed gateway in their
   advertisements.

3.  Relationship to BGP Link State and Egress Peer Engineering

   When a remote GW receives a route to a prefix X it can use the SR
   tunnel instances within the contained Tunnel Encapsulation attribute
   to identify the GWs through which X can be reached.  It uses this
   information to compute SR TE paths across the backbone network
   looking at the information advertised to it in SR BGP Link State
   (BGP-LS) [I-D.gredler-idr-bgp-ls-segment-routing-ext] and correlated
   using the SR domain identity.  SR Egress Peer Engineering (EPE)
   [I-D.ietf-idr-bgpls-segment-routing-epe] can be used to supplement
   the information advertised in the BGP-LS.

4.  Advertising an SR Domain Route Externally

   When a packet destined for prefix X is sent on an SR TE path to a GW
   for the SR domain containing X, it needs to carry the receiving GW's
   label for X such that this label rises to the top of the stack before
   the GW completes its processing of the packet.  To achieve this we
   place a prefix-SID sub-TLV for X in each SR tunnel instance in the
   Tunnel Encapsulation attribute in the externally advertised route for
   X.



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   Alternatively, if the GWs for a given SR domain are configured to
   allow remote GWs to perform SR TE through that SR domain for a prefix
   X, then each GW computes an SR TE path through that SR domain to X
   from each of the currently active GWs, and places each in an MPLS
   label stack sub-TLV [I-D.ietf-idr-tunnel-encaps] in the SR tunnel
   instance for that GW.

5.  Encapsulation

   If the GWs for a given SR domain are configured to allow remote GWs
   to send them a packet in that SR domain's native encapsulation, then
   each GW will also include multiple instances of a tunnel TLV for that
   native encapsulation in externally advertised routes: one for each GW
   and each containing a remote endpoint sub-TLV with that GW's address.
   A remote GW may then encapsulate a packet according to the rules
   defined via the sub-TLVs included in each of the tunnel TLV
   instances.

6.  IANA Considerations

   IANA maintains a registry called "BGP parameters" with a sub-registry
   called "BGP Tunnel Encapsulation Tunnel Types."  The registration
   policy for this registry is First-Come First-Served.

   IANA is requested to assign a codepoint from this sub-registry for
   "SR Tunnel".  The next available value may be used and reference
   should be made to this document.

   [[Note: This text is likely to be replaced with a specific code point
   value once FCFS allocation has been made.]]

7.  Security Considerations

   TBD

8.  Manageability Considerations

   TBD

9.  Acknowledgements

   Thanks to Bruno Rijsman for review comments, and to Robert Raszuk for
   useful discussions.








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10.  References

10.1.  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-13 (work in progress), June 2017.

   [I-D.ietf-idr-tunnel-encaps]
              Rosen, E., Patel, K., and G. Velde, "The BGP Tunnel
              Encapsulation Attribute", draft-ietf-idr-tunnel-encaps-06
              (work in progress), June 2017.

   [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>.

   [RFC4360]  Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
              Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
              February 2006, <http://www.rfc-editor.org/info/rfc4360>.

   [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>.

10.2.  Informative References

   [I-D.gredler-idr-bgp-ls-segment-routing-ext]
              Previdi, S., Psenak, P., Filsfils, C., Gredler, H., Chen,
              M., and j. jefftant@gmail.com, "BGP Link-State extensions
              for Segment Routing", draft-gredler-idr-bgp-ls-segment-
              routing-ext-04 (work in progress), October 2016.

   [I-D.ietf-spring-segment-routing]
              Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
              and R. Shakir, "Segment Routing Architecture", draft-ietf-
              spring-segment-routing-12 (work in progress), June 2017.

   [RFC7911]  Walton, D., Retana, A., Chen, E., and J. Scudder,
              "Advertisement of Multiple Paths in BGP", RFC 7911,
              DOI 10.17487/RFC7911, July 2016,
              <http://www.rfc-editor.org/info/rfc7911>.




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Authors' Addresses

   John Drake
   Juniper Networks

   Email: jdrake@juniper.net


   Adrian Farrel
   Juniper Networks

   Email: afarrel@juniper.net


   Eric Rosen
   Juniper Networks

   Email: erosen@juniper.net


   Keyur Patel
   Arrcus, Inc.

   Email: keyur@arrcus.com


   Luay Jalil
   Verizon

   Email: luay.jalil@verizon.com





















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