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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: Informational                                  E. Rosen
Expires: October 21, 2017                               Juniper Networks
                                                                K. Patel
                                                            Arrcus, Inc.
                                                                L. Jalil
                                                                 Verizon
                                                          April 19, 2017


   Gateway Auto-Discovery and Route Advertisement for Segment Routing
                  Enabled Data Center Interconnection
                 draft-drake-bess-datacenter-gateway-03

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.

   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 data center site to which it provides access, and
   also to advertise on behalf of each other gateway to the same data
   center site.

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].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.




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   described in the Simplified BSD License.

Table of Contents

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

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



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   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.

   Suppose that there are two gateways, GW1 and GW2 as shown in
   Figure 1, for a given egress DC and that they each advertise a route
   to prefix X which is located within the egress DC 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    ------   |
             | DC Site         |                  | DC Site  |Prefix|  |
             |                 |                  |          |   X  |  |
             |                 |                  |           ------   |
             |       --        |                  |   ---         ---  |
             |      |GW|       |                  |  |GW1|       |GW2| |
              -------++---------                   ----+----------+-+--
                     | \                               |         /  |
                     |  \                              |        /   |
                     |  -+-------------        --------+-------+--  |
                     | ||PE|       ----|      |----   |PE|   |PE| | |
                     | | --       |ASBR+------+ASBR|   --     --  | |
                     | |           ----|      |----               | |
                     | |               |      |                   | |
                     | |           ----|      |----               | |
                     | | AS1      |ASBR+------+ASBR|          AS2 | |
                     | |           ----|      |----               | |
                     |  ---------------        -------------------  |
                   --+----------------------------------------------+--
                  | |PE|                                          |PE| |
                  |  --                 AS3                        --  |
                  |                                                    |
                   ----------------------------------------------------


               Figure 1: Example Data Center 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 DC sites 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
      DC advertise a route to a prefix X within the DC, they will each
      include a Tunnel Encapsulation attribute with multiple tunnel




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      instances each of type "SR tunnel", one for each 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 DC (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 data center site.  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 data center site can now see all possible
   paths to the egress data center site regardless of which route
   advertisement is propagated to it, and it can choose one or balance
   traffic flows as it sees fit.

2.  DC Gateway Auto-Discovery

   To allow a given DC'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 DC that is common
      across all GWs to the DC (i.e., across all GWs to all DC sites
      that are interconnected) and unique across all DCs that are
      connected.

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

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

   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 DC site
   (including itself), and will include these in every route advertised
   externally to the DC site 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 DC 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 DC 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 a DC Route Externally

   When a packet destined for prefix X is sent on an SR TE path to a GW
   for the DC site 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 DC are configured to allow
   remote GWs to perform SR TE through that DC for a prefix X, then each
   GW computes an SR TE path through that DC 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 DC are configured to allow remote GWs to send
   them a packet in that DC'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.

10.  References







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10.1.  Normative References

   [I-D.ietf-idr-bgpls-segment-routing-epe]
              Previdi, S., Filsfils, C., Patel, K., Ray, S., Dong, J.,
              and M. Chen, "Segment Routing BGP Egress Peer Engineering
              BGP-LS Extensions", draft-ietf-idr-bgpls-segment-routing-
              epe-11 (work in progress), March 2017.

   [I-D.ietf-idr-tunnel-encaps]
              Rosen, E., Patel, K., and G. Velde, "The BGP Tunnel
              Encapsulation Attribute", draft-ietf-idr-tunnel-encaps-04
              (work in progress), April 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-11 (work in progress), February
              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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