Evan, Thanks so much for your explanation. I learned something new already today!
Dan ----- Original Message ----- From: "Evan Pearce" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Tuesday, July 29, 2003 9:36 PM Subject: Re: [IMail Forum] Telnet Response [Was: Imail hacked...] > On 30/07/2003 at 03:56:20, Daniel Donnelly wrote: > > > So, how do you know there were control codes sent (did you use a > > sniffer)? Is there any way to tell what codes telnet will send in that > > first line (some configuration, maybe?)? > > A packet sniffer will show them up. Because Telnet was created > primarily as a way for users to log in and run terminal sessions on a > machine, it supports a whole bunch of commands and configuration > options (eg whether the server echoes text that the user types, > whether the user will be logged out if the Telnet session is dropped). > Those commands are sent as the byte 0xFF (called IAC, or Interpret As > Command) followed by one or more bytes representing the option. > > The exact string sent on startup will depend on the Telnet client and > its configuration. I just connected to IMail's SMTP server with PuTTY > in Telnet mode, and in response to the 220 message the client sent the > following bytes: > > FF FB 1F FF FB 20 FF FB 18 FF FB 27 FF FD 01 FF FB 03 FF FD 03 > > If you wanted to interpret those, FF is IAC, FB through FE represent > "will, won't, do, don't", and the byte following FB through FE is a > specific Telnet option (each of which is usually defined in its own > RFC). None of that meaning is carried across to SMTP - IMail treats it > as normal text and returns a 502 error because it saw 21 bytes of > garbage before the command. > > > Just had the thought of sending a blank line as first line, to see > > what that might do... > > It'll give you a 502, no different to if you typed a command. The > client will send those options as soon as it knows there's a server on > the other end. > > Cheers, > Evan > > > To Unsubscribe: http://www.ipswitch.com/support/mailing-lists.html > List Archive: http://www.mail-archive.com/imail_forum%40list.ipswitch.com/ > Knowledge Base/FAQ: http://www.ipswitch.com/support/IMail/ > To Unsubscribe: http://www.ipswitch.com/support/mailing-lists.html List Archive: http://www.mail-archive.com/imail_forum%40list.ipswitch.com/ Knowledge Base/FAQ: http://www.ipswitch.com/support/IMail/
