IGMP Snooping in Catalyst 2955

[eduardoherreramora]

I have an Ethernet/Ip Control Network with plcs and robots. I'm using 2955 to internetwork.

I want to improve the Network traffic using IGMP Snooping.

Does Anybody knows if 2955 needs a Router to perform the IGMP Snooping??

Can it work without Queries??

Thanks in advanced

Best Regards

[milan.kulik]

Hi,

AFAIK, router is not absolutely necessary. If you are using multicast just in one subnet (VLAN) without multicast routing, 2955 can use IGMP snooping to send multicasts inside multicast groups.

See http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2950/12120ea2/2950scg/swigmp.htm for details.

There are another useful articles about this problem:

http://www.cisco.com/warp/public/473/22.html

and

http://www.cisco.com/warp/public/473/38.html

(which says directly: "... a new feature is available called the Internet Group Management Protocol (IGMP) snooping querier. With this feature, a router is no longer required to constrain multicast traffic when the multicast source and all receivers are in the same VLAN.")

Rgeards,

Milan

[eduardoherreramora]

Hi, Thanks for your answer..

So what I understood as long as I'm using 2955 and the IGMP Snooping Querier Feature is currently not Supported in this kind of switches.. In fact I need to use a Router.

Is this Right??

Best REgards.

[milan.kulik]

Hi,

my understanding is following:

It depends on your needs.

If you need just to tune multicast traffic inside one VLAN (subnet) without routing multicast to another subnet (i.e. multicast source and detination are in the same subnet and you just want to prevent multicast flooding to all switch ports), I think you don't need a router.

See ip imgp snooping and related commands in http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2950/12120ea2/2950cr/cli1.htm#wp1082269.

If you need to route multicasts to other subnets, you need a router.

Regards,

Milan

[eduardoherreramora]

I've read the information you proposed.

I'm getting into networks that's why I'm very persistent, I want to understand what's goingo on in my network.

My need are to constraint the traffic inside one Vlan(subnet) without routing multicast to another subnet.

What I've read is that the switch snoops to the IGMP reports from the hosts,and i have 3 points

1.The router is the one that makes the queries to see which switchports want to become member of a multicast group.

2.The Querier feature ( that would do the "router work") is not available on 2955's right?

3. I've also read that when a host is first connected it sends an unsolicited igmp join message is this the only one message the switch needs to perform the snooping?

Thanks in Advanced

Regards

Eduardo Herrera

[milan.kulik]

Eduardo,

I was dealing with the same problem (Constraining Multicast Traffic with Source and

Receivers on the Same VLAN) two years ago.

I based my solution on the

http://www.cisco.com/warp/public/473/38.html article.

The IGMP snooping was not available on all my switches that time, so I had to involve CGMP and a PIM interface (without multicast routing, as described in the article) on my router.

It workd fine.

Finally I included some IGMP snooping on CatOS switches (Cat6000).

It seems to me that IGMP snooping is implemented quite different way on Cat2950s.

I've no 2950 in my network currently (I don't like them, I consider them being full of bugs), so I'm not able to test it.

But looking to the Config Guide (http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2950/12120ea2/2950scg/swigmp.htm#wp1111930), I'd say you are correct in your 1. and 2. points.

Regarding 3., I'd try to configure "no ip igmp snooping source-only-learning" on the 2950.

See

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2950/12120ea2/2950scg/swigmp.htm#wp1136702. It says "...the switch floods unknown multicast traffic to the VLAN and sends the traffic to the CPU until the traffic becomes known." This is correct, I think. But following sentence is pretty confusing to me:

"When the switch receives an IGMP report from a host for a particular multicast group, the switch forwards traffic from this multicast group only to the multicast router ports. " I really don't know what this means.

But i'd try no ip igmp snooping source-only-learning, anyway, and see if it works.

If not, I'd involve a router.

Regards,

Milan