RFC 894 (rfc894) - Page 1 of 3


Standard for the transmission of IP datagrams over Ethernet networks



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Network Working Group                                     Charles Hornig
Request for Comments: 894            Symbolics Cambridge Research Center
                                                              April 1984

 A Standard for the Transmission of IP Datagrams over Ethernet Networks


Status of this Memo

   This RFC specifies a standard method of encapsulating Internet
   Protocol (IP) [1] datagrams on an Ethernet [2].  This RFC specifies a
   standard protocol for the ARPA-Internet community.

Introduction

   This memo applies to the Ethernet (10-megabit/second, 48-bit
   addresses).  The procedure for transmission of IP datagrams on the
   Experimental Ethernet (3-megabit/second, 8-bit addresses) is
   described in [3].

Frame Format

   IP datagrams are transmitted in standard Ethernet frames.  The type
   field of the Ethernet frame must contain the value hexadecimal 0800.
   The data field contains the IP header followed immediately by the IP
   data.

   The minimum length of the data field of a packet sent over an
   Ethernet is 46 octets.  If necessary, the data field should be padded
   (with octets of zero) to meet the Ethernet minimum frame size.  This
   padding is not part of the IP packet and is not included in the total
   length field of the IP header.

   The minimum length of the data field of a packet sent over an
   Ethernet is 1500 octets, thus the maximum length of an IP datagram
   sent over an Ethernet is 1500 octets.  Implementations are encouraged
   to support full-length packets.  Gateway implementations MUST be
   prepared to accept full-length packets and fragment them if
   necessary.  If a system cannot receive full-length packets, it should
   take steps to discourage others from sending them, such as using the
   TCP Maximum Segment Size option [4].

   Note:  Datagrams on the Ethernet may be longer than the general
   Internet default maximum packet size of 576 octets.  Hosts connected
   to an Ethernet should keep this in mind when sending datagrams to
   hosts not on the same Ethernet.  It may be appropriate to send
   smaller datagrams to avoid unnecessary fragmentation at intermediate
   gateways.  Please see [4] for further information on this point.





Hornig


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