Ethereal-dev: Re: [Ethereal-dev] Sequence numbers in TCP segments

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From: Jaap Keuter <jaap.keuter@xxxxxxxxx>
Date: Thu, 8 Dec 2005 16:34:21 +0100 (CET)
On Thu, 8 Dec 2005, Victor wrote:

> Hello
>
> I've got a sample capture file which contains a set of TCP segments.
> These TCP segments have a sequence number in their corresponding header
> field. This sequence number seems to be a 32-bit random value. If I open
> the sample capture file with Ethereal, these sequence numbers appear as
> logical sequence numbers (such as 0, 17, etc.). Anybody know how
> Ethereal obtain these logical sequence numbers?

Hi,

This is a feature of the TCP dissector (which you can toggle in its
preference menu: relative sequence numbers and window scaling). If enabled
it creates a conversation to relate the TCP packets to each other and
start the counts at 0. Check packet-tcp.c for further details.

Thanx,
Jaap