Wireshark-users: Re: [Wireshark-users] Why does server resend SYN+ACK?
From: Stuart Kendrick <skendric@xxxxxxxxx>
Date: Sun, 06 May 2012 06:12:57 -0700
Hi Andrej,

I'm having similar trouble telling a story around that.

As though Frame #3 had not arrived at the Server ( ... if that were the case, then the trace would make more sense.  However, you say that you captured /on/ the Server ... so, minimally, libpcap saw Frame #3 ... I would expect the TCP stack to receive a copy as well.

(1) Does anyone know of circumstances under which libpcap acquires a copy of a frame while the TCP stack does not?

(2) Does the TCP stack report problems ( 'bad segments received') right after this experience?
linux> netstat -s
    372 active connections openings
    4509 passive connection openings
    120 failed connection attempts
    2 connection resets received
    1 connections established
    43095 segments received
    33255 segments send out
    0 segments retransmited
    0 bad segments received.
    120 resets sent

(3) Would you be willing to post a detailed view of Frames 1-3?


On 5/5/2012 10:00 PM, Andrej van der Zee wrote:

I am experiencing some weird behavior in the network traffic between a
mobile device and an Apache server 2.2 running on Linux (tried Ubuntu
and CentOS). See attachment for a packet capture on the server.

The client establishes a connection with the server in packet 1-3.
Then, for some unknown reason, the client does not send any HTTP
request. After 3 seconds, the server resends the SYN+ACK. I am trying
to understand what is going on here and why would TCP/IP resend the
SYN+ACK in packet 4?


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