draft-ietf-ospf-rfc3137bis-01.txt   draft-ietf-ospf-rfc3137bis-02.txt 
Network Working Group A. Retana Network Working Group A. Retana
Internet-Draft Hewlett-Packard Co. Internet-Draft Hewlett-Packard Co.
Obsoletes: RFC3137 (if approved) L. Nguyen Obsoletes: RFC3137 (if approved) L. Nguyen
Intended status: Informational A. Zinin Intended status: Informational A. Zinin
Expires: December 31, 2012 Cisco Systems, Inc. Expires: January 17, 2013 Cisco Systems, Inc.
R. White R. White
D. McPherson D. McPherson
Verisign, Inc. Verisign, Inc.
June 29, 2012 July 16, 2012
OSPF Stub Router Advertisement OSPF Stub Router Advertisement
draft-ietf-ospf-rfc3137bis-01 draft-ietf-ospf-rfc3137bis-02
Abstract Abstract
This memo describes a backward-compatible technique that may be used This document describes a backward-compatible technique that may be
by OSPF (Open Shortest Path First) implementations to advertise used by OSPF (Open Shortest Path First) implementations to advertise
unavailability to forward transit traffic or to lower the preference unavailability to forward transit traffic or to lower the preference
level for the paths through such a router. In some cases, it is level for the paths through such a router.
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 Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 31, 2012. This Internet-Draft will expire on January 17, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . . 3
3. Proposed Solution . . . . . . . . . . . . . . . . . . . . . . . 3 3. Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Deployment Considerations . . . . . . . . . . . . . . . . . . . 4 3.1. OSPFv3-only Solution . . . . . . . . . . . . . . . . . . . 4
4.1. Other Solutions . . . . . . . . . . . . . . . . . . . . . . 4 4. Maximum Link Metric . . . . . . . . . . . . . . . . . . . . . . 4
5. Maximum Link Metric . . . . . . . . . . . . . . . . . . . . . . 4 5. Deployment Considerations . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . . 5 8.1. Normative References . . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . . 5 8.2. Informative References . . . . . . . . . . . . . . . . . . 5
Appendix A. Changes between the -00 and -01 versions. . . . . . . 5 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . . 6
A.1. Changes between the -00 and -01 versions. . . . . . . . . . 6
A.2. Changes between the -01 and -02 versions. . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Motivation 1. Motivation
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 high 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 CPU load or does not have enough memory to store all LSAs 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 the router's own IP routers from using it for transit routing, while still routing
addresses, i.e., the router is announced as a 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. Requirements Language 2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Proposed Solution 3. 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 to 2) Allowing other routers to reach IP prefixes directly connected 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
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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 with the costs of all non-stub links (links of the types neighbors with the costs of all non-stub links (links of the types
other than 3) set to MaxLinkMetric. other than 3) set to MaxLinkMetric.
The solution above applies to both OSPFv2 [RFC2328] and OSPFv3 The solution above applies to both OSPFv2 [RFC2328] and OSPFv3
[RFC5340]. [RFC5340].
4. Deployment Considerations 3.1. 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.
4. 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.
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.
5. Deployment Considerations
When using MaxLinkMetric, some inconsistency may be seen if the When using MaxLinkMetric, some inconsistency may be seen if the
network is constructed of routers that perform intra-area Dijkstra network is constructed of routers that perform intra-area Dijkstra
calculation as specified in [RFC1247] (discarding link records in calculation as specified in [RFC1247] (discarding link records in
router-LSAs that have a MaxLinkMetric cost value) and routers that router-LSAs that have a MaxLinkMetric cost value) and routers that
perform it as specified in [RFC1583] and higher (do not treat links perform it as specified in [RFC1583] and higher (do not treat links
with MaxLinkMetric cost as unreachable). Note that this with MaxLinkMetric cost as unreachable). Note that this
inconsistency will not lead to routing loops, because if there are inconsistency will not lead to routing loops, because if there are
some alternate paths in the network, both types of routers will agree 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 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 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 first type will not use the stub router for transit (which is the
desired behavior), while the routers of the second type will still desired behavior), while the routers of the second type will still
use this path. use this path.
4.1. Other Solutions On the other hand, clearing the R-bit will consistently result in the
router not being used as transit.
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.
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 6. Security Considerations
The technique described in this document does not introduce any new The technique described in this document does not introduce any new
security issues into the OSPF protocol. security issues into the OSPF protocol.
7. Acknowledgements 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
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[RFC1247] Moy, J., "OSPF Version 2", RFC 1247, July 1991. [RFC1247] Moy, J., "OSPF Version 2", RFC 1247, July 1991.
[RFC1583] Moy, J., "OSPF Version 2", RFC 1583, March 1994. [RFC1583] Moy, J., "OSPF Version 2", RFC 1583, March 1994.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008. for IPv6", RFC 5340, July 2008.
Appendix A. Changes between the -00 and -01 versions. Appendix A. Change Log
A.1. Changes between the -00 and -01 versions.
o Defined a new architectural constant (MaxLinkMetric) to eliminate o Defined a new architectural constant (MaxLinkMetric) to eliminate
any confusion about the interpretation of LSInfinity. any confusion about the interpretation of LSInfinity.
o Added a section to reference the R-bit and V6-bit in OSPFv3. o Added a section to reference the R-bit and V6-bit in OSPFv3.
o Updated acks and contact information. o Updated acks and contact information.
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.
Authors' Addresses Authors' Addresses
Alvaro Retana Alvaro Retana
Hewlett-Packard Co. Hewlett-Packard Co.
2610 Wycliff Road 2610 Wycliff Road
Raleigh, NC 27607 Raleigh, NC 27607
USA USA
Email: alvaro.retana@hp.com Email: alvaro.retana@hp.com
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