RFC 895 (rfc895) - Page 2 of 3
Standard for the transmission of IP datagrams over experimental Ethernet networks
Alternative Format: Original Text Document
RFC 895 April 1984
Address Mappings
The mapping between 32-bit Internet addresses to 8-bit Experimental
Ethernet addresses can be done several ways.
The easiest thing to do is to use the last eight bits of host number
part of the Internet address as the host's address on the
Experimental Ethernet. This is the recommended approach.
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
Experimental Ethernet address (address zero).
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 will also be changed in the future.)
Byte Order
As described in Appendix B of the Internet Protocol
specification [1], the IP datagram is transmitted over the Ethernet
as a series of 8-bit bytes.
Postel