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Versions: (draft-retana-ospf-rfc3137bis) 00 01 02 03 04 RFC 6987

Network Working Group                                          A. Retana
Internet-Draft                                       Hewlett-Packard Co.
Obsoletes: RFC3137 (if approved)                               L. Nguyen
Intended status: Informational                                  A. Zinin
Expires: December 31, 2012                           Cisco Systems, Inc.
                                                                R. White
                                                            D. McPherson
                                                          Verisign, Inc.
                                                           June 29, 2012


                     OSPF Stub Router Advertisement
                     draft-ietf-ospf-rfc3137bis-01

Abstract

   This memo 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.  In some cases, it is
   desirable not to route transit traffic via a specific OSPF router.
   However, OSPF does not specify a standard way to accomplish this.

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
   working documents as Internet-Drafts.  The list of current Internet-
   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 December 31, 2012.

Copyright Notice

   Copyright (c) 2012 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
   carefully, as they describe your rights and restrictions with respect
   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.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . . . 3
   3.  Proposed Solution . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Deployment Considerations . . . . . . . . . . . . . . . . . . . 4
     4.1.  Other Solutions . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Maximum Link Metric . . . . . . . . . . . . . . . . . . . . . . 4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 5
   Appendix A.  Changes between the -00 and -01 versions.  . . . . . . 5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6




























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1.  Motivation

   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 proposed solution 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 prevents 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 proposed 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 will be still routed through it.


2.  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].


3.  Proposed Solution

   The solution described 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



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   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
   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].


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.

4.1.  Other Solutions

   This document describes a technique that has been implemented and
   deployed in a wide variety of networks.  OSPFv3 [RFC5340] introduced
   additional options to provide similar, if not better, control of the
   forwarding topology; the R-bit and the V6-bit provide a more granular
   indication of whether a router is active and/or whether it should be
   used specifically for IPv6 traffic, respectively.

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


5.  Maximum Link Metric

   Section 3 refers to the cost of all non-stub links as MaxLinkMetric,
   which is a new fixed architectural value introduced in this document.





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   MaxLinkMetric
      The metric value indicating that the link described by an LSA
      should not be used as transit.  Used in router-LSAs (see
      Section 3).  It is defined to be the 16-bit binary value of all
      ones: 0xffff.


6.  Security Considerations

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


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.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

8.2.  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.  Changes between the -00 and -01 versions.






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   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.


Authors' Addresses

   Alvaro Retana
   Hewlett-Packard Co.
   2610 Wycliff Road
   Raleigh, NC  27607
   USA

   Email: alvaro.retana@hp.com


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

   Email: lhnguyen@cisco.com


   Alex Zinin
   Cisco Systems, Inc.
   Capital Tower, 168 Robinson Rd.
   Singapore, Singapore  068912
   Singapore

   Email: azinin@cisco.com


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

   Email: riwhite@verisign.com







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

   Email: dmcpherson@verisign.com












































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