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TCP alternate checksum options (RFC1146)

IP.com Disclosure Number: IPCOM000001957D
Original Publication Date: 1990-Mar-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 Text document.
This is the abbreviated version, containing approximately 30% of the total text.

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:

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

| Kind=14 | Length=3 | chksum |

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

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

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 checksum.

Alternate checksum negotiation proceeds as follows:

A SYN segment used to originate a connection may contain the

Alternate Checksum Request Option, which specifies an alternate

checksum-calculation algorithm to be used for the connection. The

acknowledging SYN-ACK segment may also carry the option.

If both SYN segment...