RFC 1146 (rfc1146) - Page 1 of 5

TCP alternate checksum options

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Network Working Group                                          J. Zweig
Request for Comments: 1146                                         UIUC
Obsoletes: RFC 1145                                        C. Partridge
                                                                    BBN
                                                             March 1990


                     TCP Alternate Checksum Options

Status of This Memo

   This memo suggests a pair of TCP options to allow use of alternate
   data checksum algorithms in the TCP header.  The use of these options
   is experimental, and not recommended for production use.

   Note:  This RFC corrects errors introduced in the editing process in
   RFC 1145.

   Distribution of this memo is unlimited.

Introduction

   Some members of the networking community have expressed interest in
   using checksum-algorithms with different error detection and
   correction properties than the standard TCP checksum.  The option
   described in this memo provides a mechanism to negotiate the use of
   an alternate checksum at connection-establishment time, as well as a
   mechanism to carry additional checksum information for algorithms
   that utilize checksums that are longer than 16 bits.

Definition of the Options

   The TCP Alternate Checksum Request Option may be sent in a SYN
   segment by a TCP to indicate that the TCP is prepared to both
   generate and receive checksums based on an alternate algorithm.
   During communication, the alternate checksum replaces the regular TCP
   checksum in the checksum field of the TCP header.  Should the
   alternate checksum require more than 2 octets to transmit, the
   checksum may either be moved into a TCP Alternate Checksum Data
   Option and the checksum field of the TCP header be sent as 0, or the
   data may be split between the header field and the option.  Alternate
   checksums are computed over the same data as the regular TCP checksum
   (see TCP Alternate Checksum Data Option discussion below).

TCP Alternate Checksum Request Option

   The format of the TCP Alternate Checksum Request Option is:




Zweig & Partridge
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