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Webcast-Catalyst9k
New Member

Problem with multicast across L2 switches - no routing

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.

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Silver

Re: Problem with multicast across L2 switches - no routing

Hello Alleyn,

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.

see

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SXF/native/configuration/guide/snooigmp.html#wp1069655

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

Giuseppe

3 REPLIES
Hall of Fame Super Silver

Re: Problem with multicast across L2 switches - no routing

Hello Allayn,

you should have two options:

or you disable IGMP snooping for the involved vlan on all L2 switches on the path

or if possible make one of the switches to act as IGMP querier on the vlan (only one is needed)

I guess you are using a bridging context on the FWSM.

Hope to help

Giuseppe

New Member

Re: Problem with multicast across L2 switches - no routing

Thanks for the reply. I thought about disabling IGMP snooping after I sent the initial question. Regarding an IGMP querier, does it work to put the command under the VLAN interface if there is not an IP on that interface?

Thanks for your assistance.

Hall of Fame Super Silver

Re: Problem with multicast across L2 switches - no routing

Hello Alleyn,

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.

see

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SXF/native/configuration/guide/snooigmp.html#wp1069655

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

Giuseppe

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