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New Member

IGMP Snooping Question

With IGMP Snooping enabled on a switch (Catalsyt 2950), does it still require a multicast router? If the switch now intercepts all IGMP Join/Leave requests, then is the use of an IGMP enabled router still required?

Second question, if a a multicast router is required, in my lab I have found that the port on the switch that attaches to the multicast router is a member of all multicast groups. We don't want this. All multicat traffic is contained in differeny and dynamic ports on that one switch and don't want multicast traffic to travel to router. Is this possible?

Thanks!

James

3 REPLIES
Silver

Re: IGMP Snooping Question

Yes, a router is still required. IGMP Snooping just intercepts/snoops IGMP MAC multicast groups 0100.5e00.0001 to 01-00-5e-ff-ff-ff. IGMP snooping does not restrict Layer 2 multicast packets generated by routing protocols.

I don't quite understand your 2nd question. Can you rephrase this and ask again pls?

Here is a good URL for configuration and more information about IGMP Snooping:

http://www.cisco.com/en/US/partner/products/hw/switches/ps663/products_configuration_guide_chapter09186a00800e47e9.html#1020353

Hope this helps you,

Don

New Member

Re: IGMP Snooping Question

Hi Don. Let me better explain my 2nd question. I have a 2950 switch with a router attached to port fa0/24 of the switch. I have a multicast session active (ghost) on ports fa0/1, fa0/2 and fa0/3. Now, when I look at which ports are member of that specific multicast group, I see fa0/1, fa0/2, fa0/3 and fa0/24.

This has a negative effect on us because the multicast (ghost) session is constrained to that single 2950 switch and does not need to be sent to the router. Sending a ghost image to an uplink to a router affects all users connected to that one switch even though they are not part of the multicast group.

Hope that's clearer.

James

Silver

Re: IGMP Snooping Question

James,

There is really not to many ways around this function, as the router would have to be involved to provide RP or transit to RP functions. All I can think of, if you don't want to hit the router's interface with this is to filter the group (MAC) or to create a separate VLAN for your imaging with your Ghost application. Possibly others will see other alternatives.

Hope this helps you,

Don

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