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Re: Telnet handshaking

by ncw (Friar)
on May 18, 2001 at 02:10 UTC ( [id://81384]=note: print w/replies, xml ) Need Help??

in reply to Telnet handshaking

The telnet port probably isn't opening properly because you aren't completing the telnet negotiation sequence. I don't know whether you are familiar with this but it involves sending small cryptic binary messages to the server to negotiate with the client what options they both support. I wrote a C program to do this a while back - it just NAKed all the options the server sent it.

I discovered that some servers won't start up at all unless you perform the negotiation (Linux telnetd is one) whereas others are quite happy for you to charge in there ignoring the negotiation.

You could write the code for this, but as you've noted it is a bit of a pain. However you've got several other options.

  • Investigate Net::Telnet to negotiate for you
  • Investigate IO::Socket to make your connections and in particular the timeout parameter so you know when the connections have failed
  • Learn how to make nonblocking sockets The Perl Cookbook will help here.
  • Set an alarm - you could use my time limit module for instance.
TIMTOWDI of course!

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