Ethereal-users: Re: [Ethereal-users] Help Analysing Transaction

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From: ronnie sahlberg <ronniesahlberg@xxxxxxxxx>
Date: Tue, 25 Oct 2005 10:43:50 +1000


On 10/25/05, Jack Jackson <jack@xxxxxxxxxxxxxxx> wrote:
*.20 is unhappy, for no reason that I can see, unless it is because data
was sent with the FIN.  That is perfectly legal, but I don't think I have
ever seen an actual example before.  

Yepp, perfectly legal.   Most stacks normally send them as two distinct segments, but one situation where it is common to see it is if there were packetloss towards the end of a transaction and the tcp retransmission collapses the original data segment and the fin segment into one single segment for the retransmission.

 

Likewise I have never seen data sent
with SYN, which is also legal.

No this is not legal.   TTCP tried to experiment long time ago with this in order to  reduce the cost of latency for small shortlived transactions but issues were found with this approach (data inside the syn segment) which essentially killed TTCP off.

In TCP it is not legal to transfer data in the SYN segment.