IP multicast routers use D class addresses, which range from 224.0.0.0 to 239.255.255.255. Although you can use subnet masks to configure IP multicast address ranges, the concept of subnets does not exist for multicast group addresses. Consequently, the usual unicast conventions—where you reserve the all 0s subnets, all 1s subnets, all 0s host addresses, and all 1s host addresses—do not apply.
Internet Assigned Numbers Authority (IANA) reserves addresses from 224.0.0.0 through 224.0.0.255 for link-local network applications. Multicast-capable routers do not forward packets with an address in this range. For example, Open Shortest Path First (OSPF) uses 224.0.0.5 and 224.0.0.6, and Virtual Router Redundancy Protocol (VRRP) uses 224.0.0.18 to communicate across local broadcast network segments.
IANA also reserves the range of 224.0.1.0 through 224.0.1.255 for well-known applications. IANA assigns these addresses to specific network applications. For example, the Network Time Protocol (NTP) uses 224.0.1.1, and Mtrace uses 224.0.1.32. RFC1700 contains a complete list of these reserved addresses.
Multicast addresses in the 232.0.0.0/8 (232.0.0.0 to 232.255.255.255) range are reserved only for source-specific multicast (SSM) applications, such as one-to-many applications. While this range is the publicly reserved range for SSM applications, private networks can use other address ranges for SSM.
Finally, addresses in the range 239.0.0.0/8 (239.0.0.0 to 239.255.255.255) are administratively scoped addresses; they are reserved for use in private domains. Do not advertise these addresses outside the private domain. This multicast range is analogous to the 10.0.0.0/8, 172.16.0.0/20, and 192.168.0.0/16 private address ranges in the unicast IP space.
In a private network, only assign multicast addresses from 224.0.2.0 through 238.255.255.255 to applications that are publicly accessible on the Internet. Assign addresses in the 239.0.0.0/8 range to multicast applications that are not publicly accessible.
Although you can use a multicast address you choose on your own private network, it is generally not good design practice to allocate public addresses to private network entities. Do not use public addresses for unicast host or multicast group addresses on private networks.