Operation Manual – Multicast
H3C S5100-SI/EI Series Ethernet Switches
Chapter 1 Multicast Overview
1-7
I. IP multicast address
Internet Assigned Numbers Authority (IANA) categorizes IP addresses into five classes:
A, B, C, D, and E. Unicast packets use IP addresses of Class A, B, and C based on
network scales. Class D IP addresses are used as destination addresses of multicast
packets. Class D address must not appear in the IP address field of a source IP
address of IP packets. Class E IP addresses are reserved for future use.
In unicast data transport, a data packet is transported hop by hop from the source
address to the destination address. In an IP multicast environment, there are a group of
destination addresses (called group address), rather than one address. All the
receivers join a group. Once they join the group, the data sent to this group of
addresses starts to be transported to the receivers. All the members in this group can
receive the data packets. This group is a multicast group.
A multicast group has the following characteristics:
z
The membership of a group is dynamic. A host can join and leave a multicast
group at any time.
z
A multicast group can be either permanent or temporary.
z
A multicast group whose addresses are assigned by IANA is a permanent
multicast group. It is also called reserved multicast group.
Note that:
z
The IP addresses of a permanent multicast group keep unchanged, while the
members of the group can be changed.
z
There can be any number of, or even zero, members in a permanent multicast
group.
z
Those IP multicast addresses not assigned to permanent multicast groups can be
used by temporary multicast groups.
Class D IP addresses range from 224.0.0.0 to 239.255.255.255. For details, see
Table
1-2
.
Table 1-2
Range and description of Class D IP addresses
Class D address range
Description
224.0.0.0 to 224.0.0.255
Reserved multicast addresses (IP addresses
for permanent multicast groups). The IP
address 224.0.0.0 is reserved. Other IP
addresses can be used by routing protocols.
224.0.1.0 to 231.255.255.255
233.0.0.0 to 238.255.255.255
Available any-source multicast (ASM) multicast
addresses (IP addresses for temporary
groups). They are valid for the entire network.
