Multicast Addresses

Multicast uses Class D addresses (224.0.0.0 through 239.255.255.255). These addresses must be allocated through IANA. At the present, ISPs are unable to allocate Class D address space to their customers. Class D addresses are only required if you wish to be a multicast source. You can still receive multicast data without the need for a separate Class D address.

Many applications have been provided with a range of addresses for their use, and will dynamically assign a multicast address to sessions created using that application. For example, SDR will automatically assign a multicast address to your session, if you announce the session with SDR.

The 233.0.0.0/8 block has been set aside for multicast use for anyone with their own autonomous system number (ASN). The ASN can be written as a 16-bit binary number (left-padded with zeroes), and then inserted into the middle two octets of this address block. This provides a unique /24 block of addresses for anyone with their own AS number. For example, Sprint has ASN 1239. Written as a 16-bit binary number, this value is 00000100 11010111. By inserting this value into the middle two octets of the 233.0.0.0/8 block, we get 233.4.215.0/24, which Sprint could then use for multicast addresses. Anyone with their own assigned ASN can use this method to create a /24 block for multicast use. For more information about this, please read RFC 3180: GLOP Addressing in 233/8. At this time, you cannot create GLOP addresses from private AS numbers. RFC 3138 describes the method by which addresses from GLOP ranges defined by private AS numbers will be assigned.

If you have JavaScript enabled in your browser, you can use the calculator below to convert your ASN into multicast address space:

Enter AS Number:

Multicast address space: 233. . .0 /24

The 232.0.0.0/8 block is reserved for SSM. Please read Source-Specific Multicast for IP for more information about using that address range.

The 239.0.0.0/8 block is administratively scoped for internal use only. You can use this block within your own network for multicast sessions similar to the way that 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 are used for private unicast addresses. Traffic for any addresses in the 239.0.0.0/8 block will be filtered from appearing on the SprintLink network. For more information, please read RFC 2365: Administratively Scoped IP Multicast.

If you decide that you require static multicast addresses and do not have your own ASN, you can request them from IANA at this site: http://www.iana.org/cgi-bin/multicast.pl. Please read RFC 3171: IANA Guidelines for IPv4 Multicast Address Assignments for information on how IANA assigns multicast addresses.

If customers are unable to acquire address space through IANA, and do not have their own AS numbers to convert into GLOP 233 addresses, please let us know. We may be able to assist you in acquiring addresses.