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TCP alternate checksum options (RFC1145)

IP.com Disclosure Number: IPCOM000001956D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2000-Sep-12
Document File: 5 page(s) / 10K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

J. Zweig: AUTHOR [+2]

Abstract

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.

This text was extracted from a ASCII document.
This is the abbreviated version, containing approximately 27% of the total text.

Network Working Group J. Zweig

Request for Comments: 1145 UIUC

C. Partridge

BBN

February 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.

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:

+----------+----------+----------+

| Kind=14 | Length=3 | chksum |

+----------+----------+----------+

Here chksum is a number identifying the type of checksum to be used.

This option is not copied into each fragment, and appears only in the

first fragment.

The currently defined values of chksum are:

0 -- TCP checksum

1 -- 8-bit Fletcher's algorithm (see Appendix I)

2 -- 16-bit Fletcher's algorithm (see Appendix II)

Note that the 8-bit Fletcher algorithm gives a 16-bit checksum and

the 16-bit algorithm gives a 32-bit ch...