H3C S7500 Series Operation Manual page 430

Operation Manual – Multicast
H3C S7500 Series Ethernet Switches
information receivers), network-layer multicast addresses, namely, IP multicast
addresses are required. In addition, a technology must be available to map IP multicast
addresses to link-layer MAC multicast addresses. The following sections describe
these two types of multicast addresses:
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 addresses must not appear in the source IP address field of an IP
packets. Class E IP addresses are reserved for future use.
In unicast data transmission, a data packet is transmitted hop by hop from the source
address to the destination address. In an IP multicast environment, the destination
address of a packet is a multicast group address identifying a multicast group. All the
receivers join a group. Once they join the group, the data sent to this group of
addresses starts to be transmitted 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:
The membership of a group is dynamic. A host can join and leave a multicast
group at any time.
A multicast group can be either permanent or temporary.
A multicast group whose addresses are assigned by IANA is a permanent
multicast group. It is also called reserved multicast group.
Note that:
The IP address of a permanent multicast group keeps unchanged, while the
members of the group can be changed.
There can be any number of, or even zero, members in a permanent multicast
group.
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
1-1.
Table 1-1 Range and description of Class D IP addresses
Class D address range
224.0.0.0 to 224.0.0.255
Description
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.
1-6
Chapter 1 Multicast Overview
Table