
Configuring IP Multicasting Services
1-2 114064 Rev. B
An IP multicasting host group can consist of zero or more members and places no
restrictions on its membership. Host members can reside anywhere; they can join
and leave the group at any time; and they can be members of more than one group
at the same time. In order to receive a multicast message from a host group, a host
must be a member of the group. However, anyone can send a multicast datagram:
a host does not need to be a member of a group to send a multicast message to its
members.
In general, hosts that are members of the same group reside on different networks.
However, a range of multicast addresses (224.0.0.x) is reserved for groups that are
locally scoped. All message traffic for these hosts remains on the local network.
Hosts that belong to a group in this address range and that reside in different
networks will not receive each other’s message traffic.
Multicast Addresses
Each host group is assigned a unique multicast address. To reach all members of
the group, a sender uses the multicast address as the destination address of the
datagram.
An IP Version 4 multicast address is a Class D address (the high-order bits are set
to 1110) in the range of 224.0.0.0 to 239.255.255.255.
The block of addresses from 224.0.0.1 to 224.0.0.255 is reserved for routing
protocols and other low-level protocols. Multicast routers will not forward
datagrams with addresses in this range.
Note: Multicast data packets are affected by traffic filters. The network
administrator must ensure that traffic filters configured on a multicast router do
not prevent a host that is a member of a group from receiving packets intended
for that group.
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