From: lei tian (again.tl@gmail.com)
Date: Thu May 22 2008 - 17:17:37 ART
Hi Joe,
Thank you for correct me.
Without "no ip pim dm-fallback" implemented, what router will do with
traffic in dense mode group, I mean which interface will the traffic be sent
out?
Form my understanding, the router will check which interfaces are operated
in dense mode then the traffic will be flood to all dense mode interfaces.
If all interfaces are running sparse mode, then traffic will be sent out
nowhere.
That will not make any difference after implement "no ip pim dm-fallback".
That's why I said "no ip pim dm-fallback" doesnt do anything if all
interfaces are running sparse.
Correct me If I am wrong .
Thanks
Lei
On Thu, May 22, 2008 at 3:32 PM, Joseph Brunner <joe@affirmedsystems.com>
wrote:
> That is not true Lei Tian.
>
> "No ip pim dm-fallback" will not allow groups to flood if an rp is unknown
> for the group. The mode you run on the interfaces has nothing to do with
> how
> the group operates... just how the rp discovery/mapping activity takes
> place.
>
> Read the univercd
>
> "PIM dense mode fallback is enabled. That is, a multicast group in the
> absence of rendezvous point (RP) information will fall to dense mode,
> regardless of the interface mode configuration."
>
> Cont.
>
> "Use this command to prevent a router from falling back into PIM-DM when
> the
> RP becomes unavailable. This command also causes the router to block all
> multicast traffic for groups not specifically configured with an RP."
>
>
>
> Regarding " ip pim autorp listener"
>
> This command simply enables auto-rp discovery operations over sparse mode
> interfaces.
>
> "To cause IP multicast traffic for the two Auto-RP groups 224.0.1.39 and
> 224.0.1.40 to be Protocol Independent Multicast (PIM) dense mode flooded
> across interfaces operating in PIM sparse mode, use the ip pim autorp
> listener command in global configuration mode."
>
> So to answer the original question, disabling autorp operation on sparse
> mode interfaces by configuring "no ip pim autorp listener" can cause groups
> to revert back to dense mode operation (regardless of interface
> configuration) unless "no ip pim dm-fallback" is configured.
>
> -Joe
> Certified Bullsh*t caller #19366
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> lei
> tian
> Sent: Thursday, May 22, 2008 3:25 PM
> To: ccie
> Cc: Cisco certification
> Subject: Re: no ip pim dm-fallback vs no ip pim autorp listener
>
> Hi Amin,
>
> no ip pim dm-fallback wont do anything if run sparse-mode
> no ip pim autorp listener will disable autorp listener,
> If you are using autorp then you need to configure dummy RP for two group.
> If you are using static RP then this command doesnt do anything.
>
> Thanks
>
> Lei
>
> On Thu, May 22, 2008 at 3:16 PM, ccie <ccie@just-horizon.com> wrote:
>
> > Hello experts,
> >
> >
> >
> > What would be the difference in the result if of these two commands if I
> > run
> > pim sparse-mode
> >
> > no ip pim dm-fallback
> >
> > vs
> >
> > no ip pim autorp listener
> >
> >
> >
> > Regards,
> >
> > Amin
> >
> >
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