Outgoing Interface vanishes and reappears in sh ip mroute - Multicast

[kpsudhakar31]

Hi Team,

I have configured an end host(10.10.10.1) to receive multicast traffic for a stream 229.1.1.1. I see 10.10.10.1 as part of "sh ip igmp membership command" and as outgoing interface for "sh ip mroute 229.1.1.1" command. However after 3 mins, 10.10.10.1 vanishes from "sh ip mroute command" and re-appears again after 3 minutes. Again after 3 mins, entry disappears forever. Can someone kindly advice what could be the issue. 229.1.1.1 is alive and sending traffic to other interested hosts. Is it due to some problem with IGMP from End host?

[Jon Marshall]

Not sure I follow.

If the 10.10.10.1 is an end host you shouldn't be seeing that in the mroute output ie. you should see the interface that is connected to that IP subnet but not an entry for the end host itself.

What do you mean by "configured an end host" ie. end hosts usually run some software for multicast that sends the IGMP request to the router.

Can you clarify what you mean by the above ?

Also when the entry in the mroute table disappears (whatever that entry is) does the end host stop receiving the multicast stream ?

Jon

[kpsudhakar31]

Hi Jon,

Sorry for the confusion. What you have said is correct. I am seeing interface that is connected to the IP Subnet 10.10.10.1 as outgoing interface. And Yes, End hostis sending IGMP requests to the router. End host is not IGMPv3 supported. So I configured ssm-mapping for 229.1.1.1 with source 10.23.1.20 on router connected to end host.

Once the interface disappears from the mroute, End host does not receive any multicast stream. I dont see entry under "sh ip igmp membership" too.

[Jon Marshall]

Okay I haven't used SSM so unfortunately I may be of limited help.

So the end host supports IGMPv2 and your router has a mapping that then maps that group to 10.23.1.20 as the specific source.

Is that correct ?

The only thing I can find is a restriction on running IGMPv3 and using SSM mappings on the same interface if the end hosts support IGMPv3 but not SSM.

In the above case the hosts send IGMPv3 group reports but the router cannot interpret these properly and associate sources with the reports.

But if the end host doesn't support IGMPv3, which you say it doesn't, then running IGMPv3 together with SSM mappings on the same interface should work fine.

Jon

[kpsudhakar31]

Yeah Jon. But any idea why host is coming out of group membership after 3 minutes and joining again after 3 minutes and again leaving the group forever. 

AFAIK, Either it should maintain group membership forever if its interested in traffic else it will simply stop sending IGMP join.

[Jon Marshall]

AFAIK, Either it should maintain group membership forever if its interested in traffic else it will simply stop sending IGMP join.

Agreed although as far as I understand it won't keep sending joins, once joined it will simply respond to IGMP group membership queries from the router and I'm wondering if this is where it is going wrong.

Are there any other hosts on this subnet that have requested the stream and are mapped to the same source or it is just this one host.

Have you tried debugging the IGMP side of things on the router ?

Jon