Huawei Quidway S6500 Series Operation Manual page 288

Operation Manual - Multicast Protocol
Quidway S6500 Series Ethernet Switches
Point-to-multipoint data distribution
With the increasing popularity of multimedia services over IP network, multicast is
gaining its marketplace.
1.2 Implementation of IP Multicast
1.2.1 Multicast Addresses
In multicast mode, there are questions about where to send the information, how to
locate the destination or know the receiver. All these questions can be narrowed down
to multicast addressing. To guarantee the communication between a multicast source
and a multicast group, the network layer multicast address (namely the IP multicast
address) is required, along with the technique to correlate it with the link layer MAC
multicast address. Following is the introduction to these two kinds of addresses.
I. IP Multicast Addresses
According to the definition in Internet Assigned Number Authority (IANA), IP addresses
fall into four types: Class A, Class B, Class C and Class D. Unicast packets use IP
addresses of Class A, Class B or Class C, depending on specific packet scales.
Multicast packets use IP addresses of Class D as their destination addresses, but
Class D IP addresses cannot be contained in the source IP field of IP packets.
During unicast data transmission, a packet is transmitted "hop-by-hop" from the source
address to the destination address. However, in IP multicast environment, a packet has
more than one destination address, or a group of addresses. All the information
receivers are added to a group. Once a receiver joins the group, the data for this group
of addresses start flowing to this receiver. All members in the group can receive the
packets.
Membership here is dynamic, and a host can join or leave the group at any time. A
multicast group can be permanent or temporary. Some multicast group addresses are
allocated by IANA, and the multicast group is called permanent multicast group. The IP
addresses of a permanent multicast group are unchangeable, but its membership is
changeable, and the number of members is arbitrary. It is quite possible for a
permanent group to not a single member. Those not reserved for permanent multicast
groups can be used by temporary multicast groups. Class D multicast addresses range
from 224.0.0.0 to 239.255.255.255. More information is listed in Table 1-1 Ranges and
meanings of Class D addresses.
Huawei Technologies Proprietary
1-4
Chapter 1 Multicast Overview