Re: Core knowledge Q from Anthony J. Sequeira - Diagrams for

Andrew this is an excellent question.

The problem typically associated with rpf failure is that the unicast
routing table and the multicast rpf path are not the same. In the
example of the tunnel we may face this issue and by checkign both we
may quicly determine that the two are not in agreement and therefore
we might use the ip mroute command to quickly resolve the issue.
However, suppose a tunnel is not the scenario presented. Suppose you
are restricted from using the ip mroute command to provide a quick fix
to this well-known problem. How would you then propose to resolve the
issue?

Well I suppose I would first verify that I have enabled all interface
with the correct ip pim command as specified in my workbook. If this
fxes the problem due to an interface not being configured correctly
then it is working and I am done. However if it still is broken and
the rt still failes to be in sync with the rpf check, then I might
consider altering my routing metrics to take the desired path. Notice
I have not broken the given restrictions of using ip mroute. Many
people seem to suggest this solution. In my experiments with the
command I can usually fix this by altering the metrics of my routing
protocols and therefore alter the best path in my rt and this results
in an agreement with my rpf. We proceed to take this method and employ
it on a hop-by-hop basis until we reach the source.

On Fri, Sep 25, 2009 at 1:35 PM, ALL From_NJ <all.from.nj_at_gmail.com> wrote:
> Hello Team, happy Friday.
>
> Was thinking about the tshooting section and I saw an old post from Anthony
> which included this Q&A:
>
> Q: If you create a tunnel for multicast traffic and do not enable an
> IGP over the tunnel, what command is needed on the router that needs
> to receive the multicast feeds?
> A: ip mroute
>
> I was like wow ... ok, cool. This would not have crossed my mind in the
> past and I got to thinking about how a tshooting ticket might look.
>
> Question for the team -
>
> 1) How would you have gone about tshooting this? Start w/ a ping or
> mtrace?
> 2) How to discover these things quickly?
> 3) Does it help to see that the routers register the s,g correctly, but that
> a ping fails?
>
> My guess is that a question like this would state something like
> "administrator bob has configured his network for mcast, however when bob
> starts a mcast stream, traffic does not go through. Fix bob's network".
>
> Also - will we have a separate set of diagrams and addressing for the
> tshooting section?
>
> Rock on team, and many TIA,
>
> --
> Andrew Lee Lissitz
> all.from.nj_at_gmail.com
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html

Blogs and organic groups at http://www.ccie.net
Received on Fri Sep 25 2009 - 19:51:51 ART