Multicast Groups
IGMP - Internet Group Management Protocol (RFC 1112)
- defines how hosts tell routers which groups they are part of; available on Unix, PCs, Mac
- routers query directly connected hosts sending an IGMP query to 224.0.0.1 (i.e., all multicast systems)
- when there is more than one multicast router on a LAN, only one has to send the query
- access lists can be applied to restrict the multicast groups hosts can receive
- hosts send a single reply per group per LAN