From: akyccie (akyccie@gmail.com)
Date: Tue May 27 2008 - 07:20:31 ART
what is the final conclusion here.
1. Interface configured with Spare-mode only, if some reason RP is not
available
by default traffic will fall back to dense mode.
with the "no ip pim dm-fallback" command traffic will be dropped
2. Interface configured with Spare-dense mode, if some reason RP is not
available
by default traffic will fall back to dense mode.
with the "no ip pim dm-fallback" command traffic will be dropped
Is this the correct understanding
regds
----- Original Message -----
From: "Joseph Brunner" <joe@affirmedsystems.com>
To: "'lei tian'" <again.tl@gmail.com>
Cc: "'ccie'" <ccie@just-horizon.com>; "'Cisco certification'"
<ccielab@groupstudy.com>
Sent: Friday, May 23, 2008 2:05 AM
Subject: RE: no ip pim dm-fallback vs no ip pim autorp listener
> 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?
>
>>The ones that have received pim joins that are in the Outgoing interface
> list ;)
>
> 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.
>
>>no. the group will simply flood and prune if you are using old old code.
> Lately, we have dense mode state refresh, so rather than flooding until a
> prune is heard, the router with a dense mode >group will not flood the
> group
> if the group is not requested. Similar to sparse mode, except it is doing
> it
> per group without an RP.
>
>>again the interface modes decide how the router learns rp information. Not
> how the multicast traffic is forwarded. I tested this in my lab last year
> by
> running multicast traffic over a network of "sparse mode interfaces" with
> no
> RP configured. I obviously did not remove the "ip pim dm-fallback" default
> operation.
>
>
> 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 .
>
>>yes you are wrong the. The interfaces can do what ever they are configured
> to do. the router forwards multicasts based on the properties of the
> groups
> in the mroute table, and then looks to see if "ip pim dm-fallback" is
> configured. That is why "ip pim dm-fallback" is a default command. If the
> RP
> is lost due to interface MIS CONFIGURATION (i.e. using SPARSE with AUTO-RP
> and not using IP PIM AUTORP LISTENER, ETC) the traffic can still flow in
> dense mode for that group.
>
>
>
> Just read the whole univercd explanation of the ip pim dm-fallback command
> a
> couple of times. It will make sense to you.
>
>
>
> Thanks,
>
>
>
> Joe
>
>
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