an extension of Distance-Vector where each router maintains a table of (Destination, Cost, NextHop) tuples, and exchanges a list of (Destination, Cost) pairs with it directly connected neighbors
extending Distance-Vector to support multicast is a 2-stage process:
create a broadcast mechanism that allows packet to be forwarded to all the networks within the internet
refine this mechanism to prune back networks that do not have hosts belonging to the multicast group