Redundant Multicast switching

Question

All, I have a customer with a L2 network with multiple VLANS and consisting of multiple access switches with two L2/L3 core switches.  Both core switches have a SVI for each vlan using HSRP to provde redundant Default Gateways.
The main core switch is a Cisco 6500 (running 12.2(33)SXJ6) and the backup core switch is a Cisco 4500.
One of the applications on this network is Multicast which needs the protection of the redundant core switches (this is for a critical public infrastruction and so requires the protection, if one switch fails the other must continue to support the service).
I initially tried configuing "IP PIM DENSE-MODE" on the VLAN interfaces (one of the solutions as per Cisco doc #68131 which discribes a problem and solutions for configuring multicast on a L2 network) to make the switch act as a "mrouter".  When I configure pim on the applicatable vlan's on one (the main core) switch the multicast application/s work properly but when I then configure pim on the applicatable vlan's on the other (backup) switch igmp-snooping seems to fail and all interfaces on the vlan get the multicast traffic whether they have joined the group or not (effectively causing a DOS attack on the interfaces that haven't joined the group).
Another solution from document #66131 is to enable the igmp querier feature on the L2 switches (and I assume, remove the IP PIM configuration).  This should make the switch act as a mrouter "proxy".
I have also read the chapter (chaper 38) in the IOS configuraiton guide on "Configuring IGMP Snooping" which has a section on configuring redundant igmp snooping queriers.  I am thinking of trying the configuration this section is suggesting where I would remove the IP PIM and, instead, configure "ip igmp snooping querier" on the appropriate vlan interfaces on both switches.  Unfortunately I do not have a lab to test this out on and so am currently limited to trying this out on the actual network (scary!).
So, my questions.  First, and in general, does anyone have any words of wisdom for me?  Two, if my network only has mrouter "proxies" only but no actual mrouter (as I believe will be the case if I am only using the "querier" configurations) will that cause any problems with the multicast applications?
I am under some immediate pressure to solve this redundancy issue so any help would be greatly appreciated.

Answer 1

Steve
Can I have both IP PIM and the igmp querier configurations on the same (routed) VLAN interface?
You don't need to. The IGMP querier function is only used when you don't have PIM enabled on the vlan interface. When you enable PIM on a L3 interface it then sends out IGMP queries and the switch listens to the responses with IGMP snooping so it can record the multicast mac address to the correct ports.  If you don't have PIM enabled, something still needs to make those IGMP queries otherwise the switch has nothing to listen for. So that is what the IGMP snooping querier does. So its one or the other. With PIM enabled you do not need the querier.
To be honest i didnt understand a lot of what you said about your physical connectivity other than each switch sees the other switches via trunk links.
So when you enable PIM on the 6500 only multicast works for all clients on all switches properly. When you enable it on both switches multicast is then flooded to all interfaces on both switches ?
Cna you just clarify what you mean by all interfaces ie. do you mean all end devices on all the switches start seeing multicast traffic ?
When you enabled PIM on the 4500 did you enable it on all L3 interfaces at the same time ?
I am just trying to get a picture of which switches were affected and how they connect back to the core switches. Like i say i did not really follow your setup because i have no experience of that.  Is each access switch in effect connected to both core switches or do they only connect to one or the other ?
Jon