Date: Wed, 2 Aug 2000 15:40:55 -0500 (CDT) From: Guy Helmer <ghelmer@cs.iastate.edu> To: Clinton Xavier Berni <xavier@cs.duke.edu> Cc: freebsd-net@FreeBSD.ORG Subject: Re: confused about th_ack Message-ID: <Pine.HPX.4.05.10008021533460.5902-100000@popeye.cs.iastate.edu> In-Reply-To: <Pine.GSO.4.21.0008021450010.29950-100000@mackerel.cs.duke.edu>
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On Wed, 2 Aug 2000, Clinton Xavier Berni wrote: > I'm confused about the values for th_ack and th_seq in the tcp header. > > First let me provide some background. I'm working at the ip layer, not > tcp. Therefore in order to obtain tcp header information I use the mtod() > and mpullup() routines. If I have a tcp header and source or dest. port is > 80 then I print out the following packet header information: > ... > ip_id - the ip fragment id > ip_off - the offset of the fragment The fragment offset must be 0 for you to decode a TCP header in the packet. Each of your decodes shows an ip_off of 64... I'd suggest using "tcpdump tcp and port 80" to grab & decode the same packets you are decoding in the kernel. Compare the tcpdump results with your own code to discover whether your code is working properly. th_seq and th_ack are most likely increasing as one would expect... Hope this helps, Guy Guy Helmer, Ph.D. Candidate, Iowa State University Dept. of Computer Science Research Assistant, Dept. of Computer Science --- ghelmer@cs.iastate.edu http://www.cs.iastate.edu/~ghelmer To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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