IGMP on the 3500 series

[melnik-r]

I am about to deploy a totally new network with 4500s in core and server access, 3750s for the IDFs. I have a few old 3500 series switches on my currently flat network and I need to somehow support multicasting for a few months until I have the new network. It has only the IGMP profile commands available and I wonder why that is there if the switch doesn't support snooping. Does anyone know a work around that get me through the next few months. I appreciate any suggestions.

[Roberto Salazar]

If you are referring to 3500XL, this switches support CGMP. You can use CGMP on 3500XL for multicast services. CGMP has been first implemented by cisco to restrain multicastn traffic in a layer 2 network, because a switch is by essence not capable of looking at layer 3 packet so cannot distinguish IGMP packet. With CGMP the router is doing the interface between the hosts talking IGMP and the switches talking CGMP. Both the 4500 with SupII+ or above and the 3750 switch support IGMP snooping with can with CGMP services with no problem. IGMP Snooping capable switches between the router and the CGMP only switch can operate in IGMP_CGMP mode.

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

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[melnik-r]

Hi bosalaza

Thanks for your help. They are 3500XL switches. When the new network goes online all the old equipment will be retired. I will read the information you provided by the link. The show commands for cgmp are limited but are you saying it is on by default and will provide me a slight benefit for the next few months until they are retired? This morning I changed the multicast unit to a direct closet connection and had my laptop and desktop on another closet switch. Each went up with their own connection to distribution and the multicast passed. There must have been something wrong with the 3500XL that I was using as a test switch because it wouldn't pass through that one. I really appreciate your help.

[Roberto Salazar]

you also need to enable ip cgmp on the vlan interface facing the 3500XL. CGMP is dependent on the router to tell it which port to pass multicast. It is enabled by default so to easily diagnosed the problem, you can disable cgmp on the 3500XL and see if the receivers on the switch starts receiving multicast stream. Like I said the router needs to have ip cgmp enabled on the interface going to the switches that are capable of cgmp only.

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[melnik-r]

They all pass through the 3750 stack which is acting only as a layer 2 switch. The WAN router which will eventually be the RP is managed by Sprint and will be configured soon. I will request that CGMP be enabled but it seems to be passing through the 3750s just fine locally. I saw that the multicast address was passing through the ports that I was testing with, dynamically; and only those ports. It looks as though CGMP and IGMP were translating although as I said, the tools to see on the old 3500XLs are virtually non-existent. Thanks so much for your help.

[Roberto Salazar · Accepted solution]

on the 3750 that the 3500XL connects directly do the following:

show ip igmp snooping >> assuming you know which group you are looking for, see if the port connecitng to the 3500XL is in there.

show ip igmp snooping groups >> assuming you know which group you are looking for, see if the port connecitng to the 3500XL is in there.

show ip igmp snooping mrouter >> Just to confirm the 3750 knows which port goes to the mcast router.

And as I suggested earlier, try to disable cgmp in 3500XL see if that works, just for troubleshooting.

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[melnik-r]

I will be looking over everything I can this weekend but since I wrote to you last I checked my 3500XL fiber units and realized that the two switches I was testing through were not on there but both were on the 3750 stack. It was a 3550TP switch fiber linked into the 3750 and then through another fiber port linked to a 3500XLTP switch and the multicast past. Most of my network is fiber fed by fiber ports from that 3750 stack into 3500XL fiber switches which then distribute to the rest of my access switches in the closets, most 3550TP but a few 3500XLTP switches as well. When I tried to pick up the stream from of one of the switches off the fiber distribution 3500XL switches, it failed. My local LAN is entirely flat right now but there are Sprint managed Cisco routers at the WAN edge. Until we go through the process with them to enable translation between CGNP and IGNP is there a way to leverage the 3750 to reflect the multicast address for now? You may have indicated a way previously however I need to read more to fully understand. We will only transmitting on two multicast addresses at first and one will be routed over Sprint from our Boston office, one is on the local LAN. I still need to also read more to understand the mrouter but it may be that the 3750 at layer 2 might do no good. Would the address for mrouter be the layer 3 Sprint router? The Sprint routers are connected to the 3750 stacks but most all the access switches are fed through those 3500XL switches. I do have routing enabled for one port to go to a VLAN and subnet for the PBX but it is on one subnet and VLAN for all of the main units. Now that you know the scenario do you still I can get this to work whether before the Sprint routers are set for multicast or now somehow? I am including a diagram because it's easier to picture with a diagram.

Boy I cannot wait until all of this is replaced in a few months. We will be going to a multi VLAN, multi subnet network with a 4500 unit with advanced routing in the core. I wish I could just wait for that equipment to go online but they won't. I already owe you a dinner but I appreciate your time.

[melnik-r]

I printed out everything you wrote and I will go over it all. I'm sorry to be such a pain bosalaza.

[melnik-r]

bosalaza

I can't tell you how much your posts and documents helped me. After reading over the weekend I made some changes outlined and multicast is working fine now on the new and older switches. I had to go in and set "ip igmp snooping vlan X mrouter learn cgmp"just as you said in your last post.

That started everything working.

Thanks again