Couldn't ping the multicast address when I have the subinterfaces

[paheeradan.nagulan]

Experts,

Need your pick your brain on this issue. So I have 3 routers(iosv-3, iosv6 and iosv4) and a layer 2 switch(iol-l2-1). I'm using iosv-4 router as a multicast receiver by using the command ip igmp join-group 239.1.1.1. My goal is to ping 239.1.1.1 from iosv-3. I can ping the iosv-4 from iosv-3 using the unicast address but not with the multicast address.

At this time, iosv-6 has a sub interface of gi0/1.2  where the iosv-4 is in the vlan 2. When I don't have the sub interface, just the physical interface , i can ping the multicast address but not when I have the sub interface though. When I did the packet capture, i see the ICMP packets from iosv-3 to iosv-6. But I don't packets leaving from iosv-6 to the iosv-4.

Is there any command I have to enable when I use the sub interfaces?

Here is the "show ip mroute" on the iosv-6 router.

Here is the ip config on the iosv-6 router

Config on the iosv-4

Config on the iosv-3

[M02@rt37 · Accepted solution]

OK @paheeradan.nagulan 

Perfect what I see on screenshoot.

Please provide a screenshoot of your icmp from iosv-3

[M02@rt37 · Accepted solution]

iosv-4 can ping 3.3.3.3 ? Please check this.

[Harold Ritter · Accepted solution]

Hi @paheeradan.nagulan ,

Since you can successfully ping 239.1.1.1 when you do not use a subinterface, it appears that your multicast configuration is correct.

The issue is that iosv-6 does not receive the igmp membership report from iosv-4. You could verify this with the following command on iosv-6: "show ip igmp groups".

This is most probably due to igmp snooping being configured on iol-l2-1.

I would suggest you try disabling igmp snooping on iol-l2-1 (no ip igmp snooping) and then verify that igmp membership report is properly received on iosv-6.

If so you should be able to successfully ping 239.1.1.1 from iosv-3.

[paheeradan.nagulan · Accepted solution]

Hi @Harold Ritter ,

Right on. Once I disabled igmp snooping on the switch, I saw the entry for 239.1.1.1 on the IOSV-6 switch under "ip igmp groups". Then I was able to ping the multicast address from iosv-3 to iosv-4. Thanks again for that thought. Appreciate it.

The part I don't get is, when I had "igmp snooping enabled" on the switch, I was doing a packet capture between iosv-6 and the switch and I saw the packet for the igmp join message from the iosv-4. Still I didn't see the entry for the multicast for 239.1.1.1 though under "ip igmp groups". What could be the reason for that? 

[Harold Ritter · Accepted solution]

Hi @paheeradan.nagulan ,

> I was doing a packet capture between iosv-6 and the switch and > I saw the packet for the igmp join message from the iosv-4.

If you still have the packet capture file, you will probably see that the igmp membership report with destination address of 239.1.1.1 is being forwarded untagged towards iosv-6, despite the igmp membership query being received as tagged (vlan 2). This is why iosv-6 doesn't receive it properly.

This is most probably some sort of bug on the IOL L2 code.

[paheeradan.nagulan]

Hi @Harold Ritter ,

That's exactly what has happened. It's the bug, the culprit. Thanks again. 

[Harold Ritter]

You are very welcome @paheeradan.nagulan and thanks for the feedback