8
CONFIDENTIAL
26-Jan-04
© 2002 Procket Networks, Inc. All rights reserved.
•Multicast Routing is backwards from Unicast Routing
•Unicast Routing is concerned about where the packet is going.
•Multicast Routing is concerned about where the packet came from.
•Multicast Routing uses “Reverse Path Forwarding”
Multicast Forwarding
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