OK, let me see if I can restate my idea so as not to offend those that think I don't know what I'm talking about.
Wouldn't it be possible to write a proxy server that looked at the packets received from whatever program was sending them and checked to see if the data portion of the packet contained only one byte. Any telnet application I've ever seen (in telnet or RAW mode) sent the data you typed in to the remote socket as you typed it (one byte at a time). On the other hand any SMTP server I've ever seen sends the HELO command in a single packet. Yes, it would be possible to write a program that opened the socket and sent HELO in a single packet, but that's more work that the average bear is about to do. Also it wouldn't be a violation of the RFC for a SMTP server to send the HELO command a byte at a time, but I've never seen it. I understand the difference between the telnet protocol and the telnet application, but tell me why my proposal wouldn't work. -Walden PS. I'm not arguing in favour of this, I think it's more work that it's worth and you'd be disabling a _great_ debugging tool, but the question was posed so I answered it. -----Original Message----- From: Andrew Chan [mailto:[EMAIL PROTECTED]] Sent: Tuesday, October 23, 2001 2:23 PM To: Exchange Discussions Subject: RE: Disabling telnet sessions to ports 25, 110... Well put... People just have to realize that the TCP/IP is not a flawless protocol, though it's the most popular. So, they have to live with it if there are things that they can't do. Andrew, MCSE (NT & W2K) + CCNA -----Original Message----- From: Benjamin Scott [mailto:[EMAIL PROTECTED]] Posted At: Tuesday, October 23, 2001 11:11 AM Posted To: NewsgroupDiscussion Conversation: Disabling telnet sessions to ports 25, 110... Subject: RE: Disabling telnet sessions to ports 25, 110... On Tue, 23 Oct 2001, Walden H. Leverich wrote: > I know this wouldn't be easy, but what if you wrote a proxy server for > port 25. That proxy server would look to see if it was receiving one > character at a time (implying telnet) or one line at a time (implying > another SMTP server). Okay, let me try to kill this misconception once again. :-) There is a protocol called "Telnet", described in RFC-845 and RFC-855. It describes a "network teletype". There is also a program called "Telnet". It implements the protocol described in RFC-845 and RFC-855. The program called "Telnet" has a second mode of operation. If you pass a TCP port number as the second argument, instead of opening a Telnet connection, it opens a raw TCP connection to the host specified by the first argument. This connection *IS NOT* the Telnet protocol. It is simply one end of a TCP stream. When operating in this mode, the program is indistinguishable from any other TCP program -- such as an SMTP client. When one speaks of "telneting to port 25", they really mean, "using the 'Telnet' program to open a raw TCP connection to port 25". You cannot block this, any more than you can block just Outlook Express version 5.00.2615.200 from connecting to TCP port 25. Sorry, folks. :-) -- Ben Scott <[EMAIL PROTECTED]> | The opinions expressed in this message are those of the author and do | not | necessarily represent the views or policy of any other person, | entity or | organization. All information is provided without | warranty of any kind. | _________________________________________________________________ List posting FAQ: http://www.swinc.com/resource/exch_faq.htm Archives: http://www.swynk.com/sitesearch/search.asp To unsubscribe: mailto:[EMAIL PROTECTED] Exchange List admin: [EMAIL PROTECTED] _________________________________________________________________ List posting FAQ: http://www.swinc.com/resource/exch_faq.htm Archives: http://www.swynk.com/sitesearch/search.asp To unsubscribe: mailto:[EMAIL PROTECTED] Exchange List admin: [EMAIL PROTECTED] _________________________________________________________________ List posting FAQ: http://www.swinc.com/resource/exch_faq.htm Archives: http://www.swynk.com/sitesearch/search.asp To unsubscribe: mailto:[EMAIL PROTECTED] Exchange List admin: [EMAIL PROTECTED]
