H3C Technologies H3C SecPath F1000-E - Manual (Page 7)

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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 2 .
Table 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 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:
• 232.0.0.0/8: SSM group addresses, and
• 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 more information, see RFC 2365.
NOTE:
•
The membership of a group is dynamic. Hosts can join or leave multicast groups at any time.
• “Glop” is a mechanism for assigning multicast addresses between different autonomous systems (ASs).
By filling an AS number into the middle two bytes of 233.0.0.0, you get 255 multicast addresses for that
AS. For more information, see RFC 2770.
Table 3 Some reserved multicast addresses
Address Description
224.0.0.1 All systems on this subnet, including hosts and routers