Re: Sockets and Telnet

On 11/03/2010, at 8:59 AM, Jon S wrote:

Ok, I got pulled off of this a while back and am trying to get something going again.

I found this on a systeminetwork.com forum from Scott from 2005. I have 2 different servers I am talking to and the first one is sending this back exactly, I am not sure what kind it is, but I can answer these negotiation requests.

x'FFFD18' = IAC DO TERMINAL-TYPE
x'FFFD20' = IAC DO TERMINAL-SPEED
x'FFFD23' = IAC DO X-DISPLAY-LOCATION
x'FFFD24' = IAC DO ENVIRON

The second is a Microsoft telnet server and I am not sure what these mean. Any ideas?

You need to get and read the current RFCs for the Telnet protocol. They describe all these values and what they mean.

x'FFFD25'

IAC DO AUTHENTICATION

x'FFFB01'

IAC WILL ECHO

x'FFFB03'

IAC WILL SUPPRESS-GO-AHEAD

x'FFFD27'

IAC DO NEW-ENVIRONMENT

x'FFFD1F'

IAC DO WINDOW-SIZE

x'FFFD00'

IAC DO BINARY

x'FFFB00'

IAC WILL BINARY

It's been a very long time since I had to mess with this stuff but as I recall if a Telnet client gets anything (DO or WILL) it doesn't understand or cannot handle then it should respond with a DONT or WONT (as appropriate) however a properly written server will presume the defined defaults (.e.g, WONT NEW-ENVIRON and DONT NEW-ENVIRON). Note that either party can initiate option negotiation and the correct response depends on who started it. If you sent a DO and you get a DO for the same option then you should ignore it. If you get a DO for which you have not sent a DO then you should send a WILL if you can handle it or a WONT if you can't. Confirmation DO and DONT should be sent too. A FSM will be your friend here.

Regards,
Simon Coulter.
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