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Network Working Group                                              M. Xu
Internet-Draft                                                   S. Yang
Expires: September 22, 2016                                        J. Wu
                                                     Tsinghua University
                                                          March 21, 2016


                 Source/Destination Routing Using BGP-4
                        draft-xu-src-dst-bgp-00

Abstract

   This document describes the changes necessary for BGP-4 to route
   traffic from a specified prefix to a specified prefix.

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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   This Internet-Draft will expire on September 22, 2016.

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   Copyright (c) 2016 IETF Trust and the persons identified as the
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   This document may contain material from IETF Documents or IETF
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   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
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   Without obtaining an adequate license from the person(s) controlling
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Theory of Routing . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Extended NLRI Encodings . . . . . . . . . . . . . . . . . . .   3
   4.  Dealing with Ambiguity  . . . . . . . . . . . . . . . . . . .   4
   5.  Src-Dst Capability  . . . . . . . . . . . . . . . . . . . . .   4
   6.  Compatibility Considerations  . . . . . . . . . . . . . . . .   5
   7.  Deployment Issues . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   5
     10.2.  Informative References . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   This specification builds on BGP-4 [RFC4271].  It defines the
   extended NLRI encodings for an appended source prefix, to define
   routes from a source prefix to a destination prefix.

   Traditionally, routing protocols make routing decisions solely based
   on destination IP addresses, packets towards the same destination
   will be delivered to the same next hop no matter where they come
   from.  However, considering policy-based routing, traffic engineering
   and security, source information is also important for making routing
   decisions.

   In this document, we extend the NLRI field to support source prefix.
   This implies not simply routing "to a destination", but routing "to
   that destination AND from a specified source".  Traffic within the
   network could be source/destination routed as well, or could be
   implicitly or explicitly routed from "any prefix", ::/0.




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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 [RFC2119].

2.  Theory of Routing

   The primary function of BGP is to exchange network reachability
   information, compute the routes towards destination prefixes, and
   select the best routes according the pre-defined selection rules.
   BGP-4 can support only those policies which conform to the
   destination-based forwarding paradigm.

   In this context, the route is qualified by a source prefix.
   Intrinsically, in traditional routing model, the object being routed
   to is a destination prefix; in the new routing model, the object
   being routed might be a destination prefix given that the packet
   sports a certain source prefix.

   Routes that lack a source prefix match any source prefix (i.e.,
   ::/0), by definition.

3.  Extended NLRI Encodings

   In order to carry the source prefix information in an UPDATE message,
   the existing NLRI encodings are extended by prepending the source
   prefix.

   The NLRI encodings specified in [RFC4271] and [RFC4760] are extended
   as following:


                     +--------------------------------+
                     | Type (4 octets)                |
                     +--------------------------------+
                     | Length (1 octet)               |
                     +--------------------------------+
                     | Prefix (variable)              |
                     +--------------------------------+


           Extended NLRI Encodings based on RFC4271 and RFC4760

   and the NLRI encoding specified in [RFC3107] is extended as the
   following:





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                     +--------------------------------+
                     | Type (4 octets)                |
                     +--------------------------------+
                     | Length (1 octet)               |
                     +--------------------------------+
                     | Label (3 octets)               |
                     +--------------------------------+
                     | ...                            |
                     +--------------------------------+
                     | Prefix (variable)              |
                     +--------------------------------+


                 Extended NLRI encodings based on RFC3107

   Type: Assinged by IANA.

   Length: Indicates the length in bits of the IP address prefix.

   Label: Carrying label information as defined in [RFC3107]

   Prefix: The Prefix field contains an IP address prefix, followed by
   enough trailing bits to make the end of the field fall on an octet
   boundary.

4.  Dealing with Ambiguity

   Ambiguity could happen when there are two routes: A and B, where
   source prefix of A is more specific than source prefix of B, and
   destination prefix of B is more specific than destination prefix of
   A.

   In this context, the matching rule follows that in
   [I-D.baker-ipv6-ospf-dst-src-routing], the FIB lookup MUST yield the
   route with the longest matching destination prefix that also matches
   the source prefix constraint.  In the event of a tie on the
   destination prefix, it MUST also match the longest matching source
   prefix among those options.

5.  Src-Dst Capability

   The capability to carry both source and destination prefixes in BGP
   udpate messages (src-dst capability) is a new BGP capability
   [RFC5492].  The Capability Code for this capability is specified in
   the IANA.  The Capability Length field of this capability is zero.






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6.  Compatibility Considerations

   To be compatible with [I-D.ietf-idr-add-paths], the Type field
   (defined in Section Section 3) should be carefully defined by IANA.

7.  Deployment Issues

   Router without src-dst capability should discard the BGP messages
   with extended NRLI, and it falls back to traditional destination-
   based routing when this happens.

8.  Security Considerations

   While source/destination routing could be used as part of a security
   solution, it could be considered similar to an access list that is
   managed by and scales with routing.

9.  IANA Considerations

   The Type field in Section Section 3, and the new capability code
   should be defined by IANA.

10.  References

10.1.  Normative References

   [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>.

   [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>.

   [RFC3107]  Rekhter, Y. and E. Rosen, "Carrying Label Information in
              BGP-4", RFC 3107, DOI 10.17487/RFC3107, May 2001,
              <http://www.rfc-editor.org/info/rfc3107>.

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



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10.2.  Informative References

   [I-D.ietf-idr-add-paths]
              Walton, D., Retana, A., Chen, E., and J. Scudder,
              "Advertisement of Multiple Paths in BGP", draft-ietf-idr-
              add-paths-10 (work in progress), October 2014.

   [I-D.baker-ipv6-ospf-dst-src-routing]
              Baker, F., "IPv6 Source/Destination Routing using OSPFv3",
              draft-baker-ipv6-ospf-dst-src-routing-03 (work in
              progress), August 2013.

Authors' Addresses

   Mingwei Xu
   Tsinghua University
   Department of Computer Science, Tsinghua University
   Beijing  100084
   P.R. China

   Phone: +86-10-6278-1572
   Email: xumw@tsinghua.edu.cn


   Shu Yang
   Graduate School at Shenzhen, Tsinghua University
   Division of Information Science and Technology
   Shenzhen  518055
   P.R. China

   Phone: +86-755-2603-6059
   Email: yang.shu@sz.tsinghua.edu.cn


   Jianping Wu
   Tsinghua University
   Department of Computer Science, Tsinghua University
   Beijing  100084
   P.R. China

   Phone: +86-10-6278-5983
   Email: jianping@cernet.edu.cn









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