Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Community Member

Multicast Constainment in Flat Network

I will be deploying 2 4900M switches uplinked together in a network for intensive video applications. My question is how to constrain multicast traffic with these 2 switches. Since the network is flat there is no real interfaces required except for management. Should I configure a vlan 1 interface on one of the switches and ip pim sparse mode on that interface along with IGMP snooping on both switches? Would this act as a means to constrain Multicast traffic? Would this require the IP Base or Enhanced for the 4900M switches?

Or should I get a router instead and create a superfluous subnet?

thanks for help

2 ACCEPTED SOLUTIONS

Accepted Solutions
Super Bronze

Re: Multicast Constainment in Flat Network

In brief, IGMP's purpose is to keep a multicast router informed whether there are hosts that want to receive specific multicast addressed traffic. The multicast router will occasionally poll or query all hosts to see if they want to continue to receive an active multicast stream (this precludes forwarding a multicast stream if hosts no longer desire the traffic and don't provide the [later IGMP ver.] "leave" message).

IGMP snooping "taps" the IGMP messages between the multicast (normally a) router and the multicast receiving hosts. If there is no mulicast querier, IGMP snooping won't function correctly. Some other device needs to generate the multicast IGMP queries (which often can be enabled by IGMP snooping capable switches).

Hall of Fame Super Bronze

Re: Multicast Constainment in Flat Network

It is available in all images as its part of the IGMP Snooping process.

HTH,

__

Edison.

9 REPLIES
Hall of Fame Super Bronze

Re: Multicast Constainment in Flat Network

You need to do nothing. IGMP Snooping is enabled by default and you don't need a Layer3 interface for IGMP Snooping to work as it relies on Layer2 information.

Please refer to the documentation for more info:

http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/50sg/configuration/guide/multi.html

HTH,

__

Edison.

Community Member

Re: Multicast Constainment in Flat Network

Thanks Edison,

This is exactly what i thought. Is this becuase the clients requesting multicast group traffic still send igmp joins through the snooping switch even though there is no router to recieve it the switch still snoops the join message?

I will rate shortly. Thanks again. Just want to be clear about explanation.

Hall of Fame Super Bronze

Re: Multicast Constainment in Flat Network

Your understanding is correct. It's snooping IGMP information in Layer2.

__

Edison.

Super Bronze

Re: Multicast Constainment in Flat Network

Although the reference Edison provided notes IGMP snooping is enabled by default, it appears a IGMP querier is also needed and, if not provided by a router, this feature is supported on the switch but is not enabled by default. See http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/50sg/configuration/guide/multi.html#wp1163405

Community Member

Re: Multicast Constainment in Flat Network

Yes!!

I had this notion as well. Thanks for confirming. While the previous argument makes logical sense to me, I haven't a clear understanding why there is this exception. Could you give me a brief explanation.

I will read link as well.

Super Bronze

Re: Multicast Constainment in Flat Network

In brief, IGMP's purpose is to keep a multicast router informed whether there are hosts that want to receive specific multicast addressed traffic. The multicast router will occasionally poll or query all hosts to see if they want to continue to receive an active multicast stream (this precludes forwarding a multicast stream if hosts no longer desire the traffic and don't provide the [later IGMP ver.] "leave" message).

IGMP snooping "taps" the IGMP messages between the multicast (normally a) router and the multicast receiving hosts. If there is no mulicast querier, IGMP snooping won't function correctly. Some other device needs to generate the multicast IGMP queries (which often can be enabled by IGMP snooping capable switches).

Community Member

Re: Multicast Constainment in Flat Network

Thanks Joseph for kind explanations.

Last question:

Will 4900M with IP Base IOS provide this 'IGMP Snooping Querier' capability?

Or will it require the Enhanced image? It's cost BTW to upgrade is outrageous!

I don't actually have the switch yet otherwise i would try the command myself.

Hall of Fame Super Bronze

Re: Multicast Constainment in Flat Network

It is available in all images as its part of the IGMP Snooping process.

HTH,

__

Edison.

Community Member

Re: Multicast Constainment in Flat Network

Good to know. Thanks.

565
Views
14
Helpful
9
Replies
CreatePlease to create content