What are the features on IGMPv2?

In the last chapter, we have seen that once a device stops listening to the multicast group address, he will not report this to the router who in turn will keep flowing the multicast stream until the timer on his IGMP Group table is expired. In another term, IGMPv1 doesn’t have a “leave” mechanism.

IGMPv2 came as an enhancement for IGMPv1, and it has new features. The features are:

Leave group messages: when a host does not want to listen to the multicast group, then it will report this to the router. The thing that IGMPv1 was not doing it.

Group specific membership query: in IGMPv1, the router must send a membership query to every single device which waste a lot of traffic in our network because this is happening periodically. With IGMPv2, the router sends one membership query for specific group address. This means, in case you have in your LAN 100 hosts, the router doesn’t need anymore to send to each of the hosts a membership query. In case he hears from 1 device a membership report, that’s enough to keep sending the multicast traffic out of its interface.

Querier election process: in case you have 2 routers in the same subnet able to send the membership query messages, only 1 will do so. This is happening after an election to ensure that only 1 router become the active querier. The router which has the lowest IP address becomes the active querier.

Those are the most important features on IGMPv2. I will do a LAB on IGMPv2 which is the same as the one we have done on IGMPv1, but I will show you that once you close the VLC player on the host side, then on MikroTik we won’t see anymore the IGMP Group entry of that host.


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