RFC 988 (rfc988) - Page 3 of 20

Host extensions for IP multicasting

RFC 988                                                        July 1986
Host Extensions for IP Multicasting


   Level 1: support for sending but not receiving multicast IP
   datagrams.

      Level 1 allows a host to partake of some multicast-based services,
      such as resource location or status reporting, but it does not
      allow a host to create or join any host groups.  An IP
      implementation may be upgraded from level 0 to level 1 very easily
      and with little new code.  Only sections 4, 5, and 6 of this memo
      are applicable to level 1 implementations.

   Level 2: full support for IP multicasting.

      Level 2 allows a host to create, join and leave host groups, as
      well as send IP datagrams to host groups.  It requires
      implementation of the Internet Group Management Protocol (IGMP)
      and extension of the IP and local network service interfaces
      within the host.  All of the following sections of this memo are
      applicable to level 2 implementations.

4.  HOST GROUP ADDRESSES

   Host groups are identified by class D IP addresses, i.e. those with
   "1110" as their high-order four bits.  The remaining 28 bits are
   unstructured as far as hosts are concerned.  The addresses of
   well-known, permanent groups are to be published in "Assigned
   Numbers". Class E IP addresses, i.e. those with "1111" as their
   high-order four bits, are reserved for future addressing modes.

   Appendix II contains some background discussion of several issues
   related to host group addresses.



















Deering