Multiple multicast sources and PIM DM

Unanswered Question
Jul 21st, 2009

Hi there,

I am seeing the following output for one of my multicast groups:

(*,, 3w2d/stopped, RP, flags: DC

Incoming interface: Null, RPF nbr

Outgoing interface list:

Vlan3462, Forward/Sparse-Dense, 3d04h/00:00:00, H

Vlan1, Forward/Sparse-Dense, 4d18h/00:00:00, H

Vlan320, Forward/Sparse-Dense, 3w2d/00:00:00, H

Vlan310, Forward/Sparse-Dense, 3w2d/00:00:00, H

Vlan300, Forward/Sparse-Dense, 3w2d/00:00:00, H

(,, 00:00:31/00:02:28, flags:

Incoming interface: Null, RPF nbr

Outgoing interface list:

Vlan300, Forward/Sparse-Dense, 00:00:31/00:00:00, H

Vlan310, Forward/Sparse-Dense, 00:00:31/00:00:00, H

Vlan320, Forward/Sparse-Dense, 00:00:31/00:00:00, H

Vlan1, Forward/Sparse-Dense, 00:00:31/00:00:00, H

Vlan3462, Forward/Sparse-Dense, 00:00:31/00:00:00, H

(,, 07:25:33/00:02:59, flags: T

Incoming interface: Vlan3462, RPF nbr, Mroute

Outgoing interface list:

Vlan300, Forward/Sparse-Dense, 07:25:33/00:00:00, H

Vlan310, Prune/Sparse-Dense, 00:00:30/00:02:29, H

Vlan320, Forward/Sparse-Dense, 07:25:33/00:00:00, H

Vlan1, Forward/Sparse-Dense, 07:25:33/00:00:00, H

What causes the S,G entry with no flags, no incoming interface, and no RPF?

My thinking is that since I have two sources for this group, my router is using PIM asserts to shutdown one of the sources. Is that accurate?

Regardless, would having two sources for this group, with all interfaces in dense mode, cause problems with the data?

Thanks in advance,


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Giuseppe Larosa Tue, 07/21/2009 - 08:42

Hello Brandon,

each (S,G) group should be treated indipendentently.

Possible reasons for what you see is an RPF check failure for source1

you can check this with

sh ip rpf

if traffic for (S1,G) is received on an interface that is not the one that the node would use to reach S1 an RPF check failure occurs.

PIM is running in dense mode because states are timed with a timer of 3 minutes:

after 2 min 28 sec a new attempt to flood traffic for group (S1,G) will be done.

(S2,G) is

(,, 07:25:33/00:02:59, flags: T

is in forwarding state since 7 hours 25 min 33 sec ago.

Hope to help


PIM assert is used when two PIM multicast routers have to decide who will be responsible for sending traffic for a (S,G) in a lan segment.

PIM assert is not used for deciding which source is legitimate.

Hope to help



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