Re: On the TCP MSS option

[Kary Rogers <kary () packetbomb com>]

Hi Jaap,

Thanks for the conversation last week and turning this around so quickly.
Thanks and see you next time!

Context for the group: A TCP connection did not have an MSS advertised in
the TCP options of the server's SYN/ACK so it defaulted to 536 bytes. Not
ideal!

-Kary

On Mon, Jun 17, 2019 at 11:27 AM Jaap Keuter <jaap.keuter () xs4all nl> wrote:

> Hi Kary,
>
> While attending your SharkFest <https://sharkfestus.wireshark.org/sf19> presentation
> on the 13th I was triggered by one remark on the TCP MSS option. This
> option was laking in one of the traces, resulting in reduced bandwidth of
> the connection. Wireshark isn’t  pointing you to this fact, while it easily
> could. It knows that it’s a SYN packet, so while dissecting the options it
> can raise a flag when the MSS option is missing.
> When we briefly talked over lunch you agreed this would be a relevant
> addition, so I went ahead and created this change
> <https://code.wireshark.org/review/#/c/33632/>. It does add two things,
> 1: an expert item to the TCP options when the SYN packet lacks an MSS
> option, and 2: an expert item to the TCP MSS option when it appears in a
> non-SYN packet. It should appear in the next release of Wireshark (v3.2).
>
> Regards,
> Jaap

-- 
Kary Rogers
http://packetbomb.com

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