Re: Odd tcp establishment sequence?

[Mohamed Lrhazi <lrhazi () gmail com>]

Thanks Allen. What's puzzling me more is why the server responds with an
ACK before it sends a SYN/ACK and why such behavior seems to sometimes
still result in connection establishment and other times not! Client just
seems to ignore the received packets.

On Tue, May 1, 2018, 4:38 PM Allen Lee <a11en1ee () pacbell net> wrote:

> The second SYN by the client is because the server didn't respond before
> the retransmission timer expiry.  There are a couple of reasons, the server
> is busy, network congestion, or circuit issues. If you haven't try it yet,
> install a protocol analyzer at the F5. .
>
>
>
>
> On Tuesday, May 1, 2018 10:31 AM, Mohamed Lrhazi <lrhazi () gmail com> wrote:
>
>
> Hello,
>
> am trying to debug why often times, my ssh client timeout trying to
> establish connection to an ssh server (F5 device)...
>
> Often times, I see a SYN sent twice, then server responding with an ACK,
> then an SYN/ACK, then my client sends RST.
>
> Other times, I see several SYN re-transmits, then ACK response, then
> SYN/ACK, then ACK from client and connection getting established!
>
> This is all not very normal, right? especially the ACK in response to a
> SYN? that should cause clients to fail to continue establishing a
> connection, right?
>
> Thanks a lot for your input, I know this is not wireshark issue!
>
> Mohamed,
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