RFC 894 (rfc894) - Page 2 of 3

Standard for the transmission of IP datagrams over Ethernet networks

RFC 894                                                       April 1984


Address Mappings

   The mapping of 32-bit Internet addresses to 48-bit Ethernet addresses
   can be done several ways.  A static table could be used, or a dynamic
   discovery procedure could be used.

   Static Table

      Each host could be provided with a table of all other hosts on the
      local network with both their Ethernet and Internet addresses.

   Dynamic Discovery

      Mappings between 32-bit Internet addresses and 48-bit Ethernet
      addresses could be accomplished through the Address Resolution
      Protocol (ARP) [5].  Internet addresses are assigned arbitrarily
      on some Internet network.  Each host's implementation must know
      its own Internet address and respond to Ethernet Address
      Resolution packets appropriately.  It should also use ARP to
      translate Internet addresses to Ethernet addresses when needed.

   Broadcast Address

      The broadcast Internet address (the address on that network with a
      host part of all binary ones) should be mapped to the broadcast
      Ethernet address (of all binary ones, FF-FF-FF-FF-FF-FF hex).

   The use of the ARP dynamic discovery procedure is strongly
   recommended.

Trailer Formats

   Some versions of Unix 4.2bsd use a different encapsulation method in
   order to get better network performance with the VAX virtual memory
   architecture.  Consenting systems on the same Ethernet may use this
   format between themselves.

   No host is required to implement it, and no datagrams in this format
   should be sent to any host unless the sender has positive knowledge
   that the recipient will be able to interpret them.  Details of the
   trailer encapsulation may be found in [6].

   (Note:  At the present time Unix 4.2bsd will either always use
   trailers or never use them (per interface), depending on a boot-time
   option.  This is expected to be changed in the future.  Unix 4.2bsd
   also uses a non-standard Internet broadcast address with a host part
   of all zeroes, this may also be changed in the future.)



Hornig