Multicasting

[Docklands]

We have a few 2960-X switches that are connected to ISR's using HSRP. The ISR's are have multicasting enabled and PIM Dense-mode on the sub-interfaces that connect to the switches. The switches have IGMP Snooping running by default. If we run VLC on two of the switches we are able to stream multicast through the routers with no problems.

However, we have hosts on one switch VLAN that need to receive multicasts from 225.225.0.1 but the host do not send out membership requests.

Is there a way of configuring the switches to requests membership of 225.225.0.1 on behalf of the hosts?

Thanks

[chrihussey · Accepted solution]

Not sure if this will fix (or put the bandaid) on the issue, but you could try putting "ip igmp join-group 225.225.0.1" on the L3 interface for that VLAN.

Regards

[Docklands]

Hi

Thank you for the reply.

I did try that but it didn't work.

Cheers

Mike

[chrihussey]

I'm not an application guy, but if the devices don't know they are supposed to join or listen to that group they just won't. The packets may arrive but just get discarded. Liken it to a broadcast that has no significance to that particular host, it will discard it.

So I guess what I am saying.maybe the application needs to be checked and not have the network compensate for the issue.

Best of luck.

[Docklands]

Agree. I have told the supplier they need to update their app so that it sends out membership requests. The network will be tested when comple by a third party (Cisco-Portcullis) so we best stick within the rules.

[Jon Marshall]

Just out of interest have you tried the command suggested but at the same time turned off IGMP snooping for that specific vlan ?

Jon

[Docklands]

I did disable the IGMP Snooping for the switch but not for that specific VLAN

[Jon Marshall]

You may have tried this already but if you haven't on the L3 interface for that vlan can you add -

"ip igmp static-group 225.225.0.1"

and see what happens.

Jon

[Joseph W. Doherty]

It may require both disablement of IGMP snooping and one of the IGMP join commands on the L3 interface.  The former to insure the multicast is delivered to L2 ports, the latter to draw the stream to the subnet.  (For the latter, PIM DM will flood and prune, so without it [and with IGMP snooping disabled] the hosts may see multicast packets they desire, but you need it to avoid the pruning the subnet.)

[Docklands]

Joseph

Please see my response to Chris.

Thanks again,

Mike

[Joseph W. Doherty]

Neat!

However, as Jon posted, having the switch actually join the group, rather than "pulling" the mcast to the subnet, can impair switch operation.  If you're unable to get the same results with the static command, and if the mcast volume become detrimental to the 2960's CPU, if the the 2960-X supports CoPP, you might be able to filter out the mcast to the 2960's CPU.

[Docklands]

Guys

Thanks. I'll check out the CPU when I return to site and let you know.

Cheers

Mike

[Docklands]

Jon/Joeseph,

Thank you I shall try your recommendations and let you know the outcome when I return to the clients premises later this week.

Mike

[Jon Marshall]

Mike

No problem.

Just to let you know I did a quick lab and with the "ip igmp join-group ..." command it did not work because I believe that simply tells the router to join the group whereas with the "ip igmp static-group ..." command it did work because that is used to pass the traffic through.

So hopefully it may work :)

Jon

[Docklands]

Jon

Please see my response to Chris.

Thanks again,

Mike