IGMP Notes

  • 2015-07-30
  • Posted by jcarvaja


This will be a series of notes about IGMP that you should know in case you are about to deploy Multicast or just studying Multicast.

  • IGMP allows host to inform routers they want to receive multicast traffic for a specific multicast group or leave a specific multicast group
  • IGMP V2 Membership Query (Type Code 0x11) and V1 Membership Report (Type Code Ox12) allows backward compatibility between IGMPv2 and IGMPv1.
  • The default version used by Systems is V2.
  • The IGMP Maximum Response Time (MRT) allows a router to define the response time for a host membership report.
  • A host when running multicast will join the group and the specific group it wants to participate. It will also start hearing on a specific MAC address per group that will be created based in the 01-00-5e-XX-XX-XX (where the bold part is the Multicast Identifier and the XX-XX-XX are the last 23 bits of the IPv4 address).
  • If there are more than one IGMP Querier Router in a LAN, the one with the Lowest IP address is the one that will send the IGMP Queries.
  • IGMPv2 Query Interval: 60 seconds (Time Period Between General Queries sent by a router).
  • IGMPv2 Query Response Interval: 10 seconds (MRT for a host to respond to general queries).
  • IGMPv2 Group Membership Interval: 260 seconds (Timer where if a router does not receive an IGMP report concludes that there are no more listeners for that Multicast Group).
  • IGMPv2 Other Querier Present Interval: 255 seconds (Timer where if the non-querier router in a LAN does not receive an IGMP query it will determine the querier router is dead and will take over).
  • IGMPv3 adds more security (It will allow devices to join a group based on their source IP address), this feature is called Source Specific Multicast (SSM).


This is just a quick summary of IGMP Notes that you can have handy in case you are studying the topic.