D-Link DES-3326 User Manual - Flooding
DES-3326 Layer 3 Fast Ethernet Switch User’s Guide
102
Switch Management and Operating Concepts
Multicast Routing Algorithms
An algorithm is not a program. An algorithm is a statement of how
a problem can be solved. A program is written to implement an
algorithm.
Multicast packets are delivered by constructing multicast trees
where the multicast router is the trunk, the branches are the
various subnetworks that may be present, and the leaves are end
recipients of the multicast packets. Several algorithms have been
developed to construct these trees and to prune branches that have
no active mulitcast group members.
Flooding
The simplest algorithm for the delivery of multicast packets is for
the multicast router to forward a multicast packet to all interfaces.
This is referred to as flooding. An equally simple refinement of
flooding is to have the router check to determine if a given
multicast packet has been received before (in a certain amount of
time). If it has, then the packet does not need to be forwarded at
all and can be dropped. If the packet is being received for the first
time, it should be flooded to all interface, except the interface on
which it was received. This will ensure that all routers on the
network will receive at least one copy of the multicast packet.
There are some obvious disadvantages to this simple algorithm.
Flooding duplicates a lot of packets and uses a lot of network
bandwidth. A multicast router must also keep a record of the
multicast packets it has received (for a period of time) to determine
if a given packet has been previously received. So flooding uses a
lot of router memory.