Lectures notes for 2010 - KTH

IGMP Version 3 [4]
• Joining a multicast group, but with a specified set of sender(s) -- so that
a client can limit the set of senders which it is interested in hearing from
(i.e., source filtering)
• all IGMP replies are now set to a single layer 2 multicast address (e.g.,
224.0.0.22) which all IGMPv3-capable multicast routers listen to:
• because most LANs are now switched rather than shared media -- it uses less bandwidth to
not forward all IGMP replies to all ports
• most switches now support IGMP snooping -- i.e., the switch is IGMP aware and knows
which ports are part of which multicast group (this requires the switch to know which ports
other switches and routers are on -- so it can forward IGMP replies to them)
– switches can listen to this specific layer 2 multicast address - rather than having to listen
to all multicast addresses
• it is thought that rather than have end nodes figure out if all the multicast senders which it is
interested in have been replied to - simply make the switch do this work.
Maguire IGMP Version 3 [4] 8: 25 of 78
maguire@kth.se 2010.03.21 Internetworking/Internetteknik