I haven't been able to get multicast to come up between sources and receivers that have four switches between them. The sources and receivers are on a single VLAN, and for all purposes a router doesn't exist to set up PIM (which I don't think is necessary) or an IGMP querier.
=== To explain that last statement ===
We have a FWSM that has the VLAN interfaces configured, but it's running an older version of code that doesn't support PIM.
Because the firewall is providing the inter-VLAN routing, none of the switches have the VLAN interfaces configured. I suppose I could set up a VLAN interface without an IP address, but I don't think I can set up an IGMP querier any way because the documentation says to supply an IP address. I don't want to do as it would bypass the security of the FWSM.
I'd appreciate any assistance on this.
your understanding about the IGMP querier feature is correct, the ip address is used as source for the IGMP general queries so it has to belong to the subnet associated to the vlan.
and more specifically:
If there is no IP address configured on the VLAN interface, the IGMP snooping querier does not start. The IGMP snooping querier disables itself if the IP address is cleared. When enabled, the IGMP snooping querier restarts if you configure an IP address.
you should able to assign a free ip address of the subnet.
However for the presence of the FWSM you need to add a permit statement in ACL to allow Query propagation and possible anwers.
On the other part disabling IGMP snooping would mean flooding all multicast traffic out all ports of all L2 switches.
Hope to help