[Stu] 2007-10-01 Created page.

The '''Internet Checksum''' is a checksum used in (nearly?) every [IP] crossing the [Internet] or any [IP]-based network, therefore the speed of of the calculation is very iportant; oftentimes it is performed in hardware.

Many RFC's described it thusly:
!!!!!!
The checksum field is the 16 bit one's complement of the one's
complement sum of all 16 bit words in the header.  For purposes of
computing the checksum, the value of the checksum field is zero.
!!!!!!

The description of the checksum and how to calculate it are found in RFC1071 [http://www.ietf.org/rfc/rfc1071.txt] ''Computing the Internet Checksum'', with additional notes in RFC1141 [http://www.ietf.org/rfc/rfc1141.txt] ''Incremental Updating of the Internet Checksum'', and RFC 1624 [http://www.ietf.org/rfc/rfc1624.txt] ''Computation of the Internet Checksum via Incremental Update'.