Multicast on core 4500 to 3750 not working

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Setting up a simple multicast. The 4500 has the "ip multicast-routing" command on. All vlans have the "ip pim sparse-mode" and are located on the core.

The vlans are then trunked out throught the gig interfaces to the edge 3750 switches. The 3750 switches have no multicast commands on them.

WE have to sites with the exact same configs. One site works and the other does not.


I have this problem too.
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Giuseppe Larosa Sat, 08/02/2008 - 09:35

Hello Neil,

have you set up a RP rendez-vous point for your multicast streams ?

without it it can work only on the site where th sources of traffic stay.

Check where the sources of your multicast streams are with show ip mroute you can find the sources (on the working site) and then with sh ip route of the source.

It is likely that the working site is the one where the sources are located.

choice one core router loopback address and declare this address as the RP address

ip pim rp

Do it at least on the other core.

Check the igmp snooping settings on access switches C3750.

for this use sh ip igmp snooping

Hope to help



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