Wireshark · Wireshark-users: Re: [Wireshark-users] On the TCP MSS option

[Kary Rogers <kary@xxxxxxxxxxxxxx>]

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@xxxxxxxxx> wrote:

Hi Kary,

While attending your SharkFest 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. 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