H3C Technologies H3C S7500E Series Switches - Manual (Page 24)

1-7
IP multicast falls in the scope of end-to-end service. The multicast architecture involves the
following four parts:
1) Addressing mechanism: Information is sent from a multicast source to a group of receivers
through a multicast address.
2) Host registration: Receiver hosts are allowed to join and leave multicast groups dynamically.
This mechanism is the basis for group membership management.
3) Multicast routing: A multicast distribution tree (namely a forwarding path tree for multicast data
on the network) is constructed for delivering multicast data from a multicast source to receivers.
4) Multicast applications: A software system that supports multicast applications, such as video
conferencing, must be installed on multicast sources and receiver hosts, and the TCP/IP stack
must support reception and transmission of multicast data.
Multicast Addresses
To allow communication between multicast sources and multicast group members, network-layer
multicast addresses, namely, multicast IP addresses must be provided. In addition, a technique
must be available to map multicast IP addresses to link-layer multicast MAC addresses.
IP multicast addresses
1) IPv4 multicast addresses
Internet Assigned Numbers Authority (IANA) assigned the Class D address space (224.0.0.0 to
239.255.255.255) for IPv4 multicast. The specific address blocks and usages are shown in Table
1-2 .
Table 1-2 Class D IP address blocks and description
Address block Description
224.0.0.0 to 224.0.0.255
Reserved permanent group addresses. The IP address 224.0.0.0
is reserved, and other IP addresses can be used by routing
protocols and for topology searching, protocol maintenance, and
so on. Common permanent group addresses are listed in Table
1-3 . A packet destined for an address in this block will not be
forwarded beyond the local subnet regardless of the Time to Live
(TTL) value in the IP header.
224.0.1.0 to 238.255.255.255
Globally scoped group addresses. This block includes two types
of designated group addresses:
z 232.0.0.0/8: SSM group addresses, and
z 233.0.0.0/8: Glop group addresses.
239.0.0.0 to 239.255.255.255
Administratively scoped multicast addresses. These addresses
are considered to be locally rather than globally unique, and can
be reused in domains administered by different organizations
without causing conflicts. For details, refer to RFC 2365.