[理学]win32的IP多播技术.ppt

* Shared distribution tree is the path derived from a shared point through which sources and receivers must send/receive multicast data Ex: regardless of location/number of receivers, senders register with Shared Root (Router D) and always send a single copy of multicast data through the Shared Root to registered receivers Ex: regardless of location/number of sources, group members always receive forwarded multicast data from Shared Root (Router D) * Multicast Forwarding Routers must know packet origination, rather than destination (opposite of unicast) ... origination IP address denotes known source ... destination IP address denotes unknown group of receivers Multicast routing utilizes Reverse Path Forwarding (RPF) ... Broadcast: floods packets out all interfaces except incoming from source; initially assuming every host on network is part of multicast group ... Prune: eliminates tree branches without multicast group members; cuts off transmission to LANs without interested receivers ... Selective Forwarding: requires its own integrated unicast routing protocol * Reverse Path Forwarding Routers forward multicast datagrams received from incoming interface on distribution tree leading to source Routers check the source IP address against their multicast routing tables (RPF check); ensure that the multicast datagram was received on the specified incoming interface * Multicast Forwarding: RPF Checking Source floods network with multicast data Each router has a designated incoming interface (RPF interface) on which multicast data can be received from a given source Each router receives multicast data on one or more interfaces, but performs RPF check to prevent duplicate forwarding Example: Router receives multicast data on two interfaces 1) performs RPF Check on multicast data received on interface E0; RPF Check succeeds because data was received on specified incoming interface from source 1; data forwarded through all outgoing interfaces on the mu