OSPF doubt

Answered Question
Feb 23rd, 2007

HI all,

I wonder how to change the standar OSPF behaviour, here is the situation:

R1, R2 and R3 (imagine a triangle topology with three direct fiber links between them) All the links have been configured with the same cost (1).

If we have a host attached to R1 and wants to get another host based in R2 will go directly (HostA - R1 - R2 - HostB).

Now imagine that link between R1 and R2 goes down, then HostA will get HostB through R3.

The problem arises when the link between R1 and R2 flaps, I'd like to configure OSPF in the way that won't form the adjacency until link stop flapping.

Anyone know how to proceed?

thx a lot in advance

I have this problem too.
0 votes
Correct Answer by sundar.palaniappan about 9 years 7 months ago

Enrique,

There sure is a way to dampen a flapping interface from causing routing issues. IP Event Dampening will suppress a flapping interface. It supports all IGPs.

Check out this link for more info:

http://www.cisco.com/pcgi-bin/search/sr.pl?q=ip%20dampening%20ospf&res=1&uid=&country=US&language=en&siteToSearch=cisco.com&filter=p&c_u=/en/US/products/ps6350/products_configuration_guide_chapter09186a0080457c1d.html#wp1027265

HTH

Sundar

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hoogen_82 Fri, 02/23/2007 - 07:01

Increase your hello timer and dead timer to a greater value. By default it would be 10 and 40 for point to point links. Make sure its done on both routers.

HTH

Hoogen

Do rate if this soln helps :)

enriquebs Fri, 02/23/2007 - 07:22

Yes, that's the option we thought, but the idea should be something like the protocol realized about the interface is flapping, then penalize the route and wait until it stops flapping... kind of "route dampening" in BGP

thx

bvsnarayana03 Fri, 02/23/2007 - 08:11

Pls dont expect features of BGP in OSPF.

I think changing timers could be the way.

Correct Answer
sundar.palaniappan Fri, 02/23/2007 - 09:18

Enrique,

There sure is a way to dampen a flapping interface from causing routing issues. IP Event Dampening will suppress a flapping interface. It supports all IGPs.

Check out this link for more info:

http://www.cisco.com/pcgi-bin/search/sr.pl?q=ip%20dampening%20ospf&res=1&uid=&country=US&language=en&siteToSearch=cisco.com&filter=p&c_u=/en/US/products/ps6350/products_configuration_guide_chapter09186a0080457c1d.html#wp1027265

HTH

Sundar

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