RFC 922 (rfc922) - Page 2 of 12

Broadcasting Internet datagrams in the presence of subnets

RFC 922                                                     October 1984
Broadcasting Internet Datagrams in the Presence of Subnets


   When a datagram is broadcast, it imposes a cost on every host that
   hears it.  Therefore, broadcasting should not be used
   indiscriminately, but rather only when it is the best solution to a
   problem.

2. Terminology

   Because broadcasting depends on the specific data link layer in use
   on a local network, we must discuss it with reference to both
   physical networks and logical networks.

   The terms we will use in referring to physical networks are, from the
   point of view of the host sending or forwarding a broadcast:

   Local Hardware Network

      The physical link to which the host is attached.

   Remote Hardware Network

      A physical network which is separated from the host by at least
      one gateway.

   Collection of Hardware Networks

      A set of hardware networks (transitively) connected by gateways.

   The IP world includes several kinds of logical network.  To avoid
   ambiguity, we will use the following terms:

   Internet

      The DARPA Internet collection of IP networks.

   IP Network

      One or a collection of several hardware networks that have one
      specific IP network number.

   Subnet

      A single member of the collection of hardware networks that
      compose an IP network.  Host addresses on a given subnet share an
      IP network number with hosts on all other subnets of that IP
      network, but the local-address part is divided into subnet-number




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