Re: PIM Convergence Problem

John

Are we running MSDP here?

I presume RP's are A & D and now B

Is there still reachability between the MSDP peers via BGP somehow

--
BR
Tony
Sent from my iPad
On 20 Apr 2013, at 17:49, John Neiberger <jneiberger_at_gmail.com> wrote:
> I posted this on cisco-nsp yesterday and didn't get any replies, so I
> thought I'd run this past the group here.
> 
> We ran into an interesting problem last night and I'm a little stumped. It
> appears that PIM did not follow a unicast routing change after a BGP peer
> was shutdown. Imagine this simple topology:
> 
> [A] ----- [B] ------ [C] -------  [D]
> |
> |
> |
> [D]
> 
> Router A is a CRS and is forwarding PIM joins toward Router D, which is
> directly attached. We are not running an IGP here. There is only an eBGP
> session between two ASes that we manage. We shutdown the BGP session
> between A and D, which caused unicast traffic to switch to the path toward
> Router B. However, it looks like Router A did not tear down the PIM joins
> that are now no longer valid. It seems that it was still joining a lot of
> traffic that it could no longer do anything with since it would now fail
> RPF checks.
> 
> We didn't get snapshots during the event, so I can't prove that is what
> happened, but it is the only thing we've found that makes any sense. We've
> had quite a few engineers looking at it and we do have TAC on the case, but
> I thought I'd check here, as well.
> 
> Have any of you seen a situation where PIM joins stay up even when they
> shouldn't? Is there possibly an issue with an interaction between PIM and
> BGP? I've never seen this sort of behavior before, so I'm not quite sure
> what to think.
> 
> Thanks,
> John
> 
> 
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