Abstract

Session

Header Processing

Paper

9-1

Full Paper

ps.gz

Title

When the CRC and TCP Checksum Disagree

Author(s)

Jonathan Stone (Stanford University)
Craig Partridge (BBN Technologies)

Abstract:

Traces of Internet packets over the last two years show that 1 in 30,000 packets fails the TCP checksum, even on links where link-level CRCs should catch all but 1 in 4 billion errors.
Analysis of 100,000 packets which fail the TCP checksum shows the Internet has a wide variety of error sources which are not detected by link-level checksums. Analysis tools have identified nearly 100 different patterns, or likely cause, of the observed errors. These categories explain half our observe errors, and show that errors occur at all levels of the network.
From the observed rate of incorrect checksums, and excluding errors that will always be caught, we conclude that the TCP checksum will fail to detect an error for rougly 1 in 200 milllion packets. From our analysis of the cause of erros, we propose simple changes to several protocols which can decrease the rate of undetected error.