RFC 1624 (rfc1624) - Page 1 of 6


Computation of the Internet Checksum via Incremental Update



Alternative Format: Original Text Document



Network Working Group                             A. Rijsinghani, Editor
Request for Comments: 1624                 Digital Equipment Corporation
Updates: 1141                                                   May 1994
Category: Informational


                  Computation of the Internet Checksum
                         via Incremental Update

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

Abstract

   This memo describes an updated technique for incremental computation
   of the standard Internet checksum.  It updates the method described
   in RFC 1141.

Table of Contents

   1. Introduction ..........................................  1
   2. Notation and Equations ................................  2
   3. Discussion ............................................  2
   4. Examples ..............................................  3
   5. Checksum verification by end systems ..................  4
   6. Historical Note .......................................  4
   7. Acknowledgments .......................................  5
   8. Security Considerations ...............................  5
   9. Conclusions ...........................................  5
   10. Author's Address .....................................  5
   11. References ...........................................  6

1.  Introduction

   Incremental checksum update is useful in speeding up several
   types of operations routinely performed on IP packets, such as
   TTL update, IP fragmentation, and source route update.

   RFC 1071, on pages 4 and 5, describes a procedure to
   incrementally update the standard Internet checksum.  The
   relevant discussion, though comprehensive, was not complete.
   Therefore, RFC 1141 was published to replace this description
   on Incremental Update.  In particular, RFC 1141 provides a
   more detailed exposure to the procedure described in RFC 1071.
   However, it computes a result for certain cases that differs



Rijsinghani