Ethereal-users: RE: [Ethereal-users] identifying problems in captures - are there some reports t

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From: Hansang Bae <hbae@xxxxxxxxxx>
Date: Mon, 06 Sep 2004 23:59:31 -0400
On 09:48 AM 8/26/2004, David DuPre wrote:
>Topic: Network Performance Degradation - how to document it.
>I have some trace files that show servers sending the same packet 4 times and the client replies with a single packet.
>The sequence number and ACK numbers are the same for all four packets, frame number and time is only difference in the
>four packets.
>Is this kind of consistent resending of four or five packets for each single reply symptomatic of a hardware problem?
>Could it be simply bad patch cords?
>Is there a site that can help me diagnose the problem this network trace is demonstrating?

[snip]

Sounds like you are seeing triple duplicate ACKs.  This is fast-retransmission as work.  This is indicative of packet lost somewhere in the network.  You should rule out the network infrastructure first.  Divide and conquering is your friend.  Chop the network in half and see if you can duplicate the packet lost.  Binary searches can quickly find faulty network equipment.  I'm assuming you've already looked at the server/client switch ports to ensure that no errors are incrementing.

hsb