As per Relevance of the word copyright, we have this rfc below:
Network Working Group A.
Request for Comments: 3137 L.
Category: Informational R.
Cisco
A.
Nexsi
D.
Amber
June 2001
OSPF Stub Router
Status of this
This memo provides information for the Internet community. It
not specify an Internet standard of any kind. Distribution of
memo is unlimited
Copyright
Copyright (C) The Internet Society (2001). All Rights Reserved
This memo describes a backward-compatible technique that may be
by OSPF (Open Shortest Path First) implementations to
unavailability to forward transit traffic or to lower the
level for the paths through such a router. In some cases, it
desirable not to route transit traffic via a specific OSPF router
However, OSPF does not specify a standard way to accomplish this
1.
In some situations, it may be advantageous to inform routers in
network not to use a specific router as a transit point, but
route to it. Possible situations include the following
o The router is in a critical condition (for example, has
high CPU load or does not have enough memory to store all
or build the routing table).
o Graceful introduction and removal of the router to/from
network
o Other (administrative or traffic engineering) reasons
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RFC 3137 OSPF Stub Router Advertisement June 2001
Note that the proposed solution does not remove the router from
topology view of the network (as could be done by just flushing
router's router-LSA), but prevents other routers from using it
transit routing, while still routing packets to router's own
addresses, i.e., the router is announced as stub
It must be emphasized that the proposed solution provides
benefits in networks designed with at least some level of
so that traffic can be routed around the stub router. Otherwise
traffic destined for the networks reachable through such a
router will be still routed through it
2. Proposed
The solution described in this document solves two
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
performing the Dijkstra calculation
2) Allowing other routers to reach IP prefixes directly
to router X
Note that it would be easy to address issue 1) alone by just
router X's router-LSA from the domain. However, it does not
problem 2), since other routers will not be able to use links
router X in Dijkstra (no back link), and because router X will
have links to its neighbors
To address both problems, router X announces its router-LSA to
neighbors as follows
o costs of all non-stub links (links of the types other than 3)
are set to LSInfinity (16-bit value 0xFFFF, rather than 24-
value 0xFFFFFF used in summary and AS-external LSAs).
o costs of stub links (type 3) are set to the interface
cost
This addresses issues 1) and 2).
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RFC 3137 OSPF Stub Router Advertisement June 2001
3. Compatibility
Some inconsistency may be seen when the network is constructed of
routers that perform intra-area Dijkstra calculation as specified
[RFC1247] (discarding link records in router-LSAs that
LSInfinity cost value) and routers that perform it as specified
[RFC1583] and higher (do not treat links with LSInfinity cost
unreachable). Note that this inconsistency will not lead to
loops, because if there are some alternate paths in the network,
types of routers will agree on using them rather than the
through the stub router. If the path through the stub router is
only one, the routers of the first type will not use the stub
for transit (which is the desired behavior), while the routers of
second type will still use this path
4.
The authors of this document do not make any claims on
originality of the ideas described. Among other people, we
like to acknowledge Henk Smit for being part of one of the
discussions around this topic
5. Security
The technique described in this document does not introduce any
security issues into OSPF protocol
6.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC1247] Moy, J., "OSPF Version 2", RFC 1247, July 1991.
[RFC1583] Moy, J., "OSPF Version 2", RFC 1583, March 1994.
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RFC 3137 OSPF Stub Router Advertisement June 2001
7. Authors'
Alvaro
7025 Kit Creek Rd
Research Triangle Park, NC 27709
EMail: aretana@cisco.
Liem
7025 Kit Creek Rd
Research Triangle Park, NC 27709
EMail: lhnguyen@cisco.
Russ
Cisco Systems, Inc
7025 Kit Creek Rd
Research Triangle Park, NC 27709
EMail: riw@cisco.
Alex
Nexsi
1959 Concourse
San Jose,CA 95131
EMail: azinin@nexsi.
Danny
Amber
48664 Milmont
Fremont, CA 94538
EMail: danny@ambernetworks.
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RFC 3137 OSPF Stub Router Advertisement June 2001
8. Full Copyright
Copyright (C) The Internet Society (2001). All Rights Reserved
This document and translations of it may be copied and furnished
others, and derivative works that comment on or otherwise explain
or assist in its implementation may be prepared, copied,
and distributed, in whole or in part, without restriction of
kind, provided that the above copyright notice and this paragraph
included on all such copies and derivative works. However,
document itself may not be modified in any way, such as by
the copyright notice or references to the Internet Society or
Internet organizations, except as needed for the purpose
developing Internet standards in which case the procedures
copyrights defined in the Internet Standards process must
followed, or as required to translate it into languages other
English
The limited permissions granted above are perpetual and will not
revoked by the Internet Society or its successors or assigns
This document and the information contained herein is provided on
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE
Funding for the RFC Editor function is currently provided by
Internet Society
Retana, et al. Informational [Page 5]
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