TMS zl Management and Configuration Guide ST.1.1.100430

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Routing
Multicast
It is not hard to imagine the challenges broadcast messages pose for packet
containment. A malfunctioning or misconfigured device can congest an entire
network. Even properly functioning devices must flood all hosts with unnec-
essary information just to send a message to the hosts that do need it.
IP multicasting addresses these problems by allowing a host to send a message
to a select group.
Figure 9-21. Multicasting
Multicast Addresses
The destination address in the IP header of a multicast message is the
multicast address. Only hosts that have joined the group for this multicast
address receive the message. (See Figure 9-21.)
Multicast addresses fall between 224.0.0.0 and 239.255.255.255. The addresses
between 224.0.0.0 and 224.0.0.255 are reserved for routing messages, and are
intended for groups such as all routers on a subnet, all OSPF routers, or all
Dynamic Host Configuration Protocol (DHCP) servers. Private organizations
can designate other multicast addresses for their own purposes. Private
multicast addresses for local networks range from 239.255.0.0 to
239.255.255.255. (For a list of multicast addresses, visit http://www.iana.org/
assignments/multicast-addresses.)
Host Groups
Network nodes forward multicast packets to the proper host group. The host
group for a multicast address is the set of hosts, or endpoints, who need to
receive messages sent to that address. Group membership is dynamic. End-