Just been reading the above RFC. To quote "Checksum is the 16-bit one's complement of the one's complement sum of a pseudo header of information from the IP header, the UDP header, and the data, padded with zero octets at the end (if necessary) to make a multiple of two octets.
The pseudo header conceptually prefixed to the UDP header contains the source address, the destination address, the protocol, and the UDP length. This information gives protection against misrouted datagrams. This checksum procedure is the same as is used in TCP." This business about a pseudo header is bothering me. If the IP header has already had a checksum that runs across the source and destination address then why does UDP do this again ? It also creates an obvious dependancy of UDP on IP also. Another question about padding making a multiple of two octets. I seem to remember Novell IPX requiring even numbered packets (2.X) maybe. Is this something to do with 16 bit processors working more efficiently with an even packet sizes i.e reading two bytes at a time was less expensive processor-wise than reading an odd byte ? Phil. __________________________________________________ Do You Yahoo!? Everything you'll ever need on one web page from News and Sport to Email and Music Charts http://uk.my.yahoo.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=26283&t=26283 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
