[c-nsp] multicast on transit LAN

Phil Mayers p.mayers at imperial.ac.uk
Tue Feb 16 12:19:27 EST 2010

On 02/16/2010 04:45 PM, Marco Regini wrote:
> Hi Phil, all my cisco are routing the multicast, the problem is that
> the l3 link between them are not point-to-point.

Understood. You have the config:

layer3 -- layer2 -- (...) -- layer2 -- layer3

...and the multicast needs to pass between the layer3 devices.

The layer3 devices are using PIM to speak to each other, yes?

In which case, you need PIM snooping on the layer2 devices.

What are the layer2 devices? How many are there? Who runs them?

> I tried to enable rgmp,cgmp ... but seems they assumes the apparatus
> being a router or a switch ( if the cisco has a svi on the vlan 100
> it is a router, if not is a switch). I'am not sure if proxing the

I'm sorry, I don't understand you.

RGMP and CGMP are different things, which serve different purposes.

> IGMP will works, because IGMP snooping probably has the same
> limitation, but I want to tray; do you know how to enable it?
> This is a pseudo configuration of apparatus, what lines I need to
> proxy the IGMP arriving to the access interface Fa0/30?

I'm sorry, I don't understand. That configuration cannot possibly work.

Can you give a more detailed configuration?

I've never used IGMP proxy on a cisco, and upon examination it looks 
like it might be a different feature than I thought - the docs seem to 
link it to unidirectional tunnels.

You really need PIM snooping.

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