D-Link DES-3326S manual Reverse Path Broadcasting RPB, 117

DES-3326S Layer 3 Fast Ethernet Switch User’s Guide

Reverse Path Broadcasting (RPB)

The Reverse Path Broadcasting (RPB) algorithm is an enhancement of the multicast spanning tree algorithm. RPB constructs a spanning tree for each multicast source. When the router receives a multicast packet, it then checks to determine if the packet was received on the shortest path back from the router to the source. If the packet was received on the shortest path back to the source, the packet is forwarded on all links except the link on which the packet was received. If the packet was not received on the shortest link back to the source, the packet is dropped.

If a link-state routing protocol is in use, RPB on a local router can determine if the path from the source through the local router to an immediately neighboring router. If it is not, the packet will be dropped at the next router and the packet should not be forwarded.

If a distance-vector routing protocol is in use, a neighboring router can either advertise its previous hop for the source as part of its routing update messages. This will ‘poison-reverse’ the route (or have the local router prune the branch from the multicast source to the neighboring router because the neighboring router has a better route from the source to the next router or subnetwork).

Since multicast packets are forwarded through the shortest route between source and destination, RPB is fast. A given router also does not need information about the entire spanning tree, nor does it need a mechanism to stop the forwarding of packets.

RPB does not use multicast group membership information in its forwarding decisions.

Switch Management and Operating Concepts 117