[c-nsp] Need help with setting up ip multicastrouting

[John Neiberger]

> It sounds like you might be describing a case where
> - IGMP snooping is enabled on a switch
> - There's no IGMP querier on the VLAN
>
> If so, then we're in agreement.  That doesn't work (though it may appear to work at first).
>
> There's a fourth option on some L2 switching platforms: enable an IGMP querier on the L2 device.  The queries don't have to come from anywhere sensible.*  As long as queries "just appear" on the LAN, clients will reply, and the IGMP snooping switch can eat the host reports that come in reply to his bogus queries.  No L3 interface required.
>
> Definitely don't try to run IGMP snooping without a querier.
>

At some point, depending on the topology (and especially if it's a
one-off thing), it might make sense to set up a GRE tunnel between the
endpoints and just run PIM on the tunnel.

John