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
IPv4 multicast addresses
Internet Assigned Numbers Authority (IANA) assigned the Class D address space (184.108.40.206 to
220.127.116.11) for IPv4 multicast. The specific address blocks and usages are shown in
Table 1-2 Class D IP address blocks and description
18.104.22.168 to 22.214.171.124
126.96.36.199 to 188.8.131.52
184.108.40.206 to 220.127.116.11
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 18.104.22.168, you get 255 multicast
addresses for that AS. For more information, refer to RFC 2770.
Table 1-3 Some reserved multicast addresses
Reserved permanent group addresses. The IP address 22.214.171.124
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
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.
Globally scoped group addresses. This block includes two types
of designated group addresses:
126.96.36.199/8: SSM group addresses, and
188.8.131.52/8: Glop group addresses.
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.
All systems on this subnet, including hosts and routers
All multicast routers on this subnet
Distance Vector Multicast Routing Protocol (DVMRP) routers
Open Shortest Path First (OSPF) routers
OSPF designated routers/backup designated routers