Tuesday, April 27, 2010

Linux telnet option negotiation - passive

Telnet client that comes with Debian Lenny (Linux Netkit 0.17) or Cygwin 1.7 telnet 1.7 (GNU inetutils) actively initiates option negotiation with the server. This is fine for most cases but there are old servers that just stops sending data when it does not like the option that the client tried to negotiate.

To passively participate in option negotiation, telnet can run with the following argument to force it not to send any further negotiation:
telnet <hostname> <port>
Note here that we specified the port number. By doing so, we are basically telling telnet that negotiation is done and so wait for any packet from the server.

And for old telnet server, the following .telnetrc maybe needed:
DEFAULT set echo mode character set crlf


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