rfc3137.txt   draft-ietf-ospf-rfc3137bis-03.txt >
Network Working Group A. Retana Network Working Group A. Retana
Request for Comments: 3137 L. Nguyen Internet-Draft L. Nguyen
Category: Informational R. White Obsoletes: 3137 (if approved) Cisco Systems, Inc.
Cisco Systems Intended status: Informational A. Zinin
A. Zinin Expires: July 21, 2013 Cinarra Systems
Nexsi Systems R. White
D. McPherson D. McPherson
Amber Networks Verisign, Inc.
June 2001 January 17, 2013
OSPF Stub Router Advertisement 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 Status of this Memo
This memo provides information for the Internet community. It does This Internet-Draft is submitted in full conformance with the
not specify an Internet standard of any kind. Distribution of this provisions of BCP 78 and BCP 79.
memo is unlimited.
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 21, 2013.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved. Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
Abstract This document is subject to BCP 78 and the IETF Trust's Legal
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described in the Simplified BSD License.
This memo describes a backward-compatible technique that may be used Table of Contents
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.
1. Motivation 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
1. Introduction
In some situations, it may be advantageous to inform routers in a 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 network not to use a specific router as a transit point, but still
route to it. Possible situations include the following. route to it. Possible situations include the following:
o The router is in a critical condition (for example, has very o The router is in a critical condition (for example, has very high
high CPU load or does not have enough memory to store all LSAs CPU load or does not have enough memory to store all LSAs or build
or build the routing table). the routing table).
o Graceful introduction and removal of the router to/from the o Graceful introduction and removal of the router to/from the
network. network.
o Other (administrative or traffic engineering) reasons. o Other (administrative or traffic engineering) reasons.
Note that the proposed solution does not remove the router from the Note that the solution introduced in this document does not remove
topology view of the network (as could be done by just flushing that the router from the topology view of the network (as could be done by
router's router-LSA), but prevents other routers from using it for just flushing that router's router-LSA), but discourages other
transit routing, while still routing packets to router's own IP routers from using it for transit routing, while still routing
addresses, i.e., the router is announced as stub. 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 It must be emphasized that the solution provides real benefits in
benefits in networks designed with at least some level of redundancy networks designed with at least some level of redundancy so that
so that traffic can be routed around the stub router. Otherwise, traffic can be routed around the stub router. Otherwise, traffic
traffic destined for the networks reachable through such a stub destined for the networks reachable through such a stub router may
router will be still routed through it. still be routed through it.
2. Proposed Solution 2. Solutions
The solution described in this document solves two challenges The solution introduced in this document solves two challenges
associated with the outlined problem. In the description below, associated with the outlined problem. In the description below,
router X is the router announcing itself as a stub. router X is the router announcing itself as a stub.
1) Making other routers prefer routes around router X while 1) Making other routers prefer routes around router X while
performing the Dijkstra calculation. performing the Dijkstra calculation.
2) Allowing other routers to reach IP prefixes directly connected 2) Allowing other routers to reach IP prefixes directly connected to
to router X. router X.
Note that it would be easy to address issue 1) alone by just flushing 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 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 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 router X in Dijkstra (no back link), and because router X will not
have links to its neighbors. have links to its neighbors.
To address both problems, router X announces its router-LSA to the To address both problems, router X announces its router-LSA to the
neighbors as follows. neighbors with the costs of all non-stub links (links of the types
other than 3) set to MaxLinkMetric.
o costs of all non-stub links (links of the types other than 3) The solution above applies to both OSPFv2 [RFC2328] and OSPFv3
are set to LSInfinity (16-bit value 0xFFFF, rather than 24-bit [RFC5340].
value 0xFFFFFF used in summary and AS-external LSAs).
o costs of stub links (type 3) are set to the interface output 2.1. OSPFv3-only Solution
cost.
This addresses issues 1) and 2). 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.
3. Compatibility issues It is left to network operators to decide which technique to use in
their network.
Some inconsistency may be seen when the network is constructed of the 3. Maximum Link Metric
routers that perform intra-area Dijkstra calculation as specified in
[RFC1247] (discarding link records in router-LSAs that have
LSInfinity cost value) and routers that perform it as specified in
[RFC1583] and higher (do not treat links with LSInfinity 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. Acknowledgements 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.
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 The authors of this document do not make any claims on the
originality of the ideas described. Among other people, we would originality of the ideas described. Among other people, we would
like to acknowledge Henk Smit for being part of one of the initial like to acknowledge Henk Smit for being part of one of the initial
discussions around this topic. discussions around this topic.
5. Security Considerations 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.
The technique described in this document does not introduce any new 8. Informative References
security issues into OSPF protocol.
6. References [RFC1247] Moy, J., "OSPF Version 2", RFC 1247, July 1991.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. [RFC1583] Moy, J., "OSPF Version 2", RFC 1583, March 1994.
[RFC1247] Moy, J., "OSPF Version 2", RFC 1247, July 1991. [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC1583] Moy, J., "OSPF Version 2", RFC 1583, March 1994. [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
7. Authors' Addresses Appendix A. Change Log
Alvaro Retana A.1. Changes between the -00 and -01 versions.
7025 Kit Creek Rd.
Research Triangle Park, NC 27709
USA
EMail: aretana@cisco.com o Defined a new architectural constant (MaxLinkMetric) to eliminate
any confusion about the interpretation of LSInfinity.
Liem Nguyen o Added a section to reference the R-bit and V6-bit in OSPFv3.
7025 Kit Creek Rd.
Research Triangle Park, NC 27709
USA
EMail: lhnguyen@cisco.com o Updated acks and contact information.
Russ White A.2. Changes between the -01 and -02 versions.
Cisco Systems, Inc.
7025 Kit Creek Rd.
Research Triangle Park, NC 27709
EMail: riw@cisco.com o Took out references to not having a standard solution and
incorporated the R-bit solution as part of the (renamed)
"Solutions" section.
Alex Zinin o Various minor edits and reordered sections.
Nexsi Systems
1959 Concourse Drive
San Jose,CA 95131
EMail: azinin@nexsi.com A.3. Changes between the -02 and -03 versions.
Danny McPherson o Updated contact information.
Amber Networks
48664 Milmont Drive
Fremont, CA 94538
EMail: danny@ambernetworks.com o Renamed the 'Motivation' section to 'Introduction' becuase of an
error in idnits.
8. Full Copyright Statement o Took out the rfc2119 references as none of the keywords are used
in the text.
Copyright (C) The Internet Society (2001). All Rights Reserved. o Added an 'IANA Considerations' section to indicate that there are
no actions required.
This document and translations of it may be copied and furnished to Authors' Addresses
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be Alvaro Retana
revoked by the Internet Society or its successors or assigns. Cisco Systems, Inc.
7025 Kit Creek Rd.
Research Triangle Park, NC 27709
USA
This document and the information contained herein is provided on an Email: aretana@cisco.com
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement Liem Nguyen
Cisco Systems, Inc.
3750 Cisco Way
San Jose, CA 95134
USA
Funding for the RFC Editor function is currently provided by the Email: lhnguyen@cisco.com
Internet Society. 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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