[Simh] Question on telnet mantra in simh

J. David Bryan jdbryan at acm.org
Wed Nov 10 23:22:49 EST 2010


Rich,


On Wednesday, November 10, 2010 at 23:08, Richard Cornwell wrote:

> Here is a patch I sent Bob back in a couple of years ago to fix telnet
> support to handle correct negotiations.

I had tried your patch back in October of 2007 when I was looking at 
improving the Telnet code, but it had two problems.  From my notes at the 
time:

 1. It causes SIMH to send a "WONT LINEMODE" upon connection, but the RFC
    prohibits this ("Parties may only request a change in option status;
    i.e., a party may not send out a 'request' merely to announce what
    mode it is in"). 

 2. It unconditionally responds to WONT with DO or DONT, which leads to
    negotiation loops (e.g., "DO BIN" from SIMH to client, "WONT BIN"
    from client, "DONT BIN" to client, "WONT BIN" from client, etc.). 

The negotiation loop showed up with the "QCTerm" HP terminal emulator.  As 
I recall, the RFC suggests that loops may be avoided by ensuring that a 
denied request is not repeated.

                                      -- Dave




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