Re: PIM Convergence Problem

That is what I suspect happened. For some reason, the mroute information
stayed in place even though unicast routing had changed, which means that
RPF had changed. A path that was no longer valid or usable was still being
used to join multicast feeds. Usually, we see the mroutes switch
immediately to follow the best unicast path, but that didn't happen this
time and we're stumped as to why. The engineers working when it happened
didn't clear any routes and didn't get any snapshots, so we're stuck with
reverse engineering the scenario based on symptoms we observed. We can't
really recreate it in production without causing noticeable problems for
people, but we're going to try to recreate it in a lab environment. Cisco
is going to try to recreate it in the lab, as well.

On Sun, Apr 21, 2013 at 11:25 AM, Tony Singh <mothafungla_at_gmail.com> wrote:

> makes sense Carlos
>
> John if all else fails clear ip mroute * on the entire path as pointed
> out, what causes this maybe to do with stale mroute information not being
> flushed, check to see if you see this prior to doing this
>
> --
> BR
>
> Tony
>
> Sent from my iPad
>
> On 21 Apr 2013, at 12:24, Carlos G Mendioroz <tron_at_huapi.ba.ar> wrote:
>
> > Hmm,
> > I may be way off, because it is ages since I played with mcast last
> > time, but PIM does not run on top of the IGP/BGP session, it runs along
> > and uses the RIB for RPF. If you have pim enabled in the interfaces and
> > you tear down the BGP session, PIM does not care. After all, it is
> > independent of the routing protocol, isn't it ?
> >
> > -Carlos
> >
> > John Neiberger @ 20/04/2013 13:49 -0300 dixit:
> >> 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.
> >
> >
> > Rakesh M @ 21/04/2013 08:10 -0300 dixit:
> >> Hi,
> >>
> >> We had a similar issue with Juniper if my memory goes right. It wont
> >> refresh until we manually give a clear command. Did you try clearing
> Pim ?
> >> Would everything get restored if you bring back the link between A and
> D ?
> >>
> >
> > --
> > Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina

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Received on Sun Apr 21 2013 - 11:56:55 ART