BFD Trigger PIM in failure and recovery problem

Unanswered Question
Dec 25th, 2009

hi all,

We have a topology in the Lab that is based on CISCO 7609 that are connected in between to switches of other vendors.

7609 is configured with BFD and PIM-SSM,OSPF.

We tested the topology backup in fiber cut scenarios and everything was ok.

We faced a problem when we powered of and on  the switch that wa sconnected to one of the 7609 at the leaf of the multicast.

when we powered of the switch the traffic switched to protection quickly.

However when we powered it on we faced and outage of 10  seconds.

The question is what is teh exact process when a switch comes up and so the 7609 detect that the link is up.

what is the process of teh BFD in reconnect ,how long does he wait in order to trigger other protocols, only ib link up or does he need to nehotiate?

Does PIM is triggered by BFD.

We tried the routing protocol with OSPF and static routing but still we got the same results.

All the BFD and PIM Timers are default



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Giuseppe Larosa Sat, 12/26/2009 - 02:35

Hello Yoram,

>> The question is what is teh exact process when a switch comes up and so the 7609 detect that the link is up.

it is not clear if the third party switch is acting as a L3 switch or a L2 switch. if it acts as a L2 switch link redundancy is managed by STP.

So there can be STP at OSI layer2.

If all links are L3 links STP does not play any role.

You have tried with static routes and OSPF so the time it takes for OSPF to load the DB is not a matter if the issue happens also with static routes.

You have BFD enabled. This can clearly provides its features for OSPF.

PIM uses information in the unicast IP routing table to perform RPF checks, independently of the unicast routing protocol in use ( protocol indipendent multicast).

In multicast configuration guide for 12.2SX we can find a chapter about subsecond multicast convergence

To be noted BFD is not mentioned in this chapter.

This is also confirmed by BFD chapter in IOS 12.2SX IP routing protocols configuration guide.

BFD can be used with unicast routing protocols, HSRP and static routes but there is no mention of PIM in the whole chapter.

The first link provides guidelines for PIM fast convergence but if the third party switches are L3 switches I'm not sure you can apply these enhancements.

Hope to help



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