OSPF Stub Router Advertisement
draft-ietf-ospf-rfc3137bis-03

Network Working Group                                          A. Retana
Internet-Draft                                                 L. Nguyen
Obsoletes: 3137 (if approved)                        Cisco Systems, Inc.
Intended status: Informational                                  A. Zinin
Expires: July 21, 2013                                   Cinarra Systems
                                                                R. White
                                                            D. McPherson
                                                          Verisign, Inc.
                                                        January 17, 2013

                     OSPF Stub Router Advertisement
                     draft-ietf-ospf-rfc3137bis-03

Abstract

   This document describes a backward-compatible technique that may be
   used by OSPF (Open Shortest Path First) implementations to advertise
   unavailability to forward transit traffic or to lower the preference
   level for the paths through such a router.

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 July 21, 2013.

Copyright Notice

   Copyright (c) 2013 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
   carefully, as they describe your rights and restrictions with respect

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   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
     2.1.  OSPFv3-only Solution  . . . . . . . . . . . . . . . . . . . 4
   3.  Maximum Link Metric . . . . . . . . . . . . . . . . . . . . . . 4
   4.  Deployment Considerations . . . . . . . . . . . . . . . . . . . 4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   8.  Informative References  . . . . . . . . . . . . . . . . . . . . 5
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . . . 5
     A.1.  Changes between the -00 and -01 versions. . . . . . . . . . 5
     A.2.  Changes between the -01 and -02 versions. . . . . . . . . . 6
     A.3.  Changes between the -02 and -03 versions. . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6

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1.  Introduction

   In some situations, it may be advantageous to inform routers in a
   network not to use a specific router as a transit point, but still
   route to it.  Possible situations include the following:

   o  The router is in a critical condition (for example, has very high
      CPU load or does not have enough memory to store all LSAs or build
      the routing table).

   o  Graceful introduction and removal of the router to/from the
      network.

   o  Other (administrative or traffic engineering) reasons.

   Note that the solution introduced in this document does not remove
   the router from the topology view of the network (as could be done by
   just flushing that router's router-LSA), but discourages other
   routers from using it for transit routing, while still routing
   packets to the router's own IP addresses, i.e., the router is
   announced as a stub.

   It must be emphasized that the solution provides real benefits in
   networks designed with at least some level of redundancy so that
   traffic can be routed around the stub router.  Otherwise, traffic
   destined for the networks reachable through such a stub router may
   still be routed through it.

2.  Solutions

   The solution introduced in this document solves two challenges
   associated with the outlined problem.  In the description below,
   router X is the router announcing itself as a stub.

   1)  Making other routers prefer routes around router X while
       performing the Dijkstra calculation.

   2)  Allowing other routers to reach IP prefixes directly connected to
       router X.

   Note that it would be easy to address issue 1) alone by just flushing
   router X's router-LSA from the domain.  However, it does not solve
   problem 2), since other routers will not be able to use links to
   router X in Dijkstra (no back link), and because router X will not
   have links to its neighbors.

   To address both problems, router X announces its router-LSA to the

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   neighbors with the costs of all non-stub links (links of the types
   other than 3) set to MaxLinkMetric.

   The solution above applies to both OSPFv2 [RFC2328] and OSPFv3
   [RFC5340].

2.1.  OSPFv3-only Solution

   OSPFv3 [RFC5340] introduced additional options to provide similar, if
   not better, control of the forwarding topology; the R-bit provides a
   more granular indication of whether a router is active and should be
   used for transit traffic.

   It is left to network operators to decide which technique to use in
   their network.

3.  Maximum Link Metric

   Section 2 refers to the cost of all non-stub links as MaxLinkMetric,
   which is a new fixed architectural value introduced in this document.

   MaxLinkMetric
      The metric value indicating that the link described by an LSA
      should not be used as transit.  Used in router-LSAs (see
      Section 2).  It is defined to be the 16-bit binary value of all
      ones: 0xffff.

4.  Deployment Considerations

   When using MaxLinkMetric, some inconsistency may be seen if the
   network is constructed of routers that perform intra-area Dijkstra
   calculation as specified in [RFC1247] (discarding link records in
   router-LSAs that have a MaxLinkMetric cost value) and routers that
   perform it as specified in [RFC1583] and higher (do not treat links
   with MaxLinkMetric cost as unreachable).  Note that this
   inconsistency will not lead to routing loops, because if there are
   some alternate paths in the network, both types of routers will agree
   on using them rather than the path through the stub router.  If the
   path through the stub router is the only one, the routers of the
   first type will not use the stub router for transit (which is the
   desired behavior), while the routers of the second type will still
   use this path.

   On the other hand, clearing the R-bit will consistently result in the
   router not being used as transit.

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5.  Security Considerations

   The technique described in this document does not introduce any new
   security issues into the OSPF protocol.

6.  IANA Considerations

   This document has no actions for IANA.

7.  Acknowledgements

   The authors of this document do not make any claims on the
   originality of the ideas described.  Among other people, we would
   like to acknowledge Henk Smit for being part of one of the initial
   discussions around this topic.

   We would also like to thank Shishio Tsuchiya, Gunter Van de Velde,
   Tomohiro Yamagata, Faraz Shamim and Acee Lindem who provided
   significant input for the latest version of this document.

8.  Informative References

   [RFC1247]  Moy, J., "OSPF Version 2", RFC 1247, July 1991.

   [RFC1583]  Moy, J., "OSPF Version 2", RFC 1583, March 1994.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, July 2008.

Appendix A.  Change Log

A.1.  Changes between the -00 and -01 versions.

   o  Defined a new architectural constant (MaxLinkMetric) to eliminate
      any confusion about the interpretation of LSInfinity.

   o  Added a section to reference the R-bit and V6-bit in OSPFv3.

   o  Updated acks and contact information.

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A.2.  Changes between the -01 and -02 versions.

   o  Took out references to not having a standard solution and
      incorporated the R-bit solution as part of the (renamed)
      "Solutions" section.

   o  Various minor edits and reordered sections.

A.3.  Changes between the -02 and -03 versions.

   o  Updated contact information.

   o  Renamed the 'Motivation' section to 'Introduction' becuase of an
      error in idnits.

   o  Took out the rfc2119 references as none of the keywords are used
      in the text.

   o  Added an 'IANA Considerations' section to indicate that there are
      no actions required.

Authors' Addresses

   Alvaro Retana
   Cisco Systems, Inc.
   7025 Kit Creek Rd.
   Research Triangle Park, NC  27709
   USA

   Email: aretana@cisco.com

   Liem Nguyen
   Cisco Systems, Inc.
   3750 Cisco Way
   San Jose, CA  95134
   USA

   Email: lhnguyen@cisco.com

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   Alex Zinin
   Cinarra Systems
   Menlo Park, CA
   USA

   Email: alex.zinin@gmail.com

   Russ White
   Verisign, Inc.
   12061 Bluemont Way
   Reston, VA  20190
   USA

   Email: riwhite@verisign.com

   Danny McPherson
   Verisign, Inc.
   21345 Ridgetop Circle
   Dulles, VA  20166
   USA

   Email: dmcpherson@verisign.com

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