RFC 894 (rfc894) - Page 2 of 3
Standard for the transmission of IP datagrams over Ethernet networks
Alternative Format: Original Text Document
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