IGMP Snooping

Hello Ananth. I will attempt to answer all of your questions in this single reply.

  1. You wrote: H1 and H2 are still interested so they will respond with a membership report. The switch will intercept these two messages and forwards them to the CPU. One of the two membership reports is then forwarded to the router. In the above statement , only one the membership report is forwarded to the router . Is this a form of report suppression? Also explain why only one report is sent?

Yes, only one membership report is forwarded to the router, however this one membership report includes all of the interfaces that want to take part in the multicast group. This is not a form of membership report suppression, because as mentioned in the lesson:

"our hosts don’t hear each others membership reports. This overrules the membership report suppression mechanism which I described in the IGMP version 2 lesson. This is required since the switch has to hear the membership report from all interfaces that need to receive the multicast traffic."
  1. You wrote: Also one more query , if the router sends a general query , the switch forwards the query to all hosts? Is that correct? Will the switch able to generate query message on its own?

Yes, that is correct. The switch will forward the query to all hosts. The switch does not generate its own queries, but transmits the queries received from the router.

  1. You wrote: It might be a dum question. How the PC has interface address as 0/1 . Normally the PC is connected to the switch right?

Rene here is using routers to act as the PCs so that information about IGMP can be viewed. That is why the interface is GigabitEthernet 0/1 on the logging output in the lesson.

  1. You wrote: In the below message, Send v2 Report for 239.1.1.1 on GigabitEthernet0/1. Which 0/1 interface it is referiing to ? Is it switch or the host interface

Again, this is the interface of the router that is playing the role of the PCs. Router with hostname H1 plays the role of Host 1 and router with hostname H2 for Host 2.

  1. You wrote: In the below message , u had mentioned the switch will send a message if any-one else is still interested? where is this message seen?

Yes, you are right. The first line should read
IGMPSN: group: Group exist - Leave for group 239.1.1.1 received on Vlan 1, port Gi0/2, group state (1)
and not Gi0/3

  1. You wrote: Also generally only one host will be connected to one port of the switch right? Then why there is a need to send the group specific query to the port when one of the host decides to leave from that port?

Actually, you may have more than one host connected to one port of a switch. What if you connect a hub to this port? (not that you would, but this must also be taken into account). What if you connect an unmanaged switch to this port? So you may have more than one host on a port…

  1. You wrote: My question here us why the switch sends the IGMP general query? [as a response to a leave group message] how different it is from a group specific query sent by a router?

For this question, Andrew has written a very good answer. Take a look at this post: https://networklessons.com/topic/igmp-snooping/#post-23806

I hope these answers have been helpful!

Laz

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