For an application I had to develop a simple telnet module. (Which I could do quickly with the help of minimalistic telnet) I did create a telnet server and a client and I used PuTTY to test the behavior of the server. PuTYY was configured for 'Telnet negotiation mode: active'.
In the server I did see the expected telnet negotiation sequence (and it was giving correct replies). The last action in the PuTTY negotiation was a strange one.
0xff 0xfe 0x32 or IAC DONT 0x32
The third byte, 0x32, is the option and that is where the problem is (for me).
I did look up all Telnet options at IANA and according to them the options range 50-137 is unassigned (0x32 is 62).
What is behind PuTTY option 0x32?
I have looked on the internet but can't find anything.
I have looked up the PuTTY documentation, same thing.
Putting up a request to the PuTTY development is severely discouraged due to capacity problems (not enough hands to type a sensible reply).
It is perfectly sensible not to use this unknown option but it still is nagging me.
What is option 0x3e supposed to do?
Problem solved. There was an error in my server code causing PuTTY to generate a reply for a non existing option.
I hereby thank Simon Tatham for the suggestion he gave leading me to find the real problem.