RFC 1936 (rfc1936) - Page 1 of 21

Implementing the Internet Checksum in Hardware

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Network Working Group                                           J. Touch
Request For Comments: 1936                                     B. Parham
Category: Informational                                              ISI
                                                              April 1996


             Implementing the Internet Checksum in Hardware

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 presents a techniques for efficiently implementing the
   Internet Checksum in hardware. It includes PLD code for programming a
   single, low cost part to perform checksumming at 1.26 Gbps.

Introduction

   The Internet Checksum is used in various Internet protocols to check
   for data corruption in headers (e.g., IP) [4] and packet bodies (e.g,
   UDP, TCP) [5][6]. Efficient software implementation of this checksum
   has been addressed in previous RFCs [1][2][3][7].

   Efficient software implementations of the Internet Checksum algorithm
   are often embedded in data copying operations ([1], Section 2). This
   copy operation is increasingly being performed by dedicated direct
   memory access (DMA) hardware. As a result, DMA hardware designs are
   beginning to incorporate dedicated hardware to compute the Internet
   Checksum during the data transfer.

   This note presents the architecture of an efficient, pipelined
   Internet Checksum mechanism, suitable for inclusion in DMA hardware
   [8]. This design can be implemented in a relatively inexpensive
   programmable logic device (PLD) (1995 cost of $40), and is capable of
   supporting 1.26 Gbps transfer rates, at 26 ns per 32-bit word.
   Appendix A provides the pseudocode for such a device. This design has
   been implemented in the PC-ATOMIC host interface hardware [8]. We
   believe this design is of general use to the Internet community.









Touch & Parham               Informational
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