H3C Technologies H3C S10500 Series Switches - Manual (Page 21)

6
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. The TCP/IP stack must
support reception and transmission of multicast data.
Multicast addresses
Network-layer multicast addresses—namely, multicast IP addresses—enables communication between
multicast sources and multicast group members. 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.
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. Other IP addresses can be used by routing protocols and
for topology searching, protocol maintenance, and so on. Table 3
lists common permanent group addresses. 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 the following
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 locally unique 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
224.0.0.2 All multicast routers on this subnet
224.0.0.3 Unassigned
224.0.0.4 Distance Vector Multicast Routing Protocol (DVMRP) routers