www.netfor2.com/tcpsum.htm That is the first website I found. I'm sure if you look some more you could probably find about 500 more. If you do not follow those instructions, you will get bad checksum returns. Just because it is an OSI layer higher does not mean it can't include data from lower down the chain. -----Original Message----- From: Antony Stone [mailto:Antony@xxxxxxxxxxxxxxxxxxxx] Sent: Friday, November 21, 2003 14:48 To: netfilter@xxxxxxxxxxxxxxxxxxx Subject: Re: Checksumming Issues On Friday 21 November 2003 8:42 pm, Hildebrand, Brian wrote: > I had to check my packet generator source code, because I thought the TCP > header was calculated the same way you do. But when I checked the source > you have to feed both the TCP and IP headers into the calculation to get a > correct checksum. It uses some information from the IP header in the > calculation (source and destination IP for example). So you don't actually > use the entire IP header, just a part of it. It is not possible that the TCP checksum depends on IP information. TCP is layer 4 of the OSI model; IP is layer 3. The IP checksum includes the TCP contents, but not the other way around. Antony. -- There's no such thing as bad weather - only the wrong clothes. - Billy Connolly Please reply to the list; please don't CC me. ---------------------------------------- The information transmitted in this message is intended only for the person or entity to whom it is addressed and may contain confidential and/or privileged material. Any review, retransmission, dissemination or other use of, or taking of any action in reliance upon this information by persons or entities other than the intended recipient is prohibited. If you received this in error, please contact the sender and destroy any copies of this document.
