Talking to a telnet server [modified]
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Hello Everyone- I am trying to build an application that connects to a telnet server and interacts with it issuing various commands. I have done this in the past and it worked relatively painlessly. This particular device I am working with today however, is using some sort of advanced feature and is sending me an authentication request as soon as I connect to it. (If I use microsoft telnet client to connect, as soon as I connect it prompts me to send my windows login information, if I say no, I am brought to a login: prompt, this is what I want to get to with my program). I have been scouring the net and I cannot find what my response should be to this server to tell it that I do not want to use the NTLM authentication, I just want to be brought to the login: prompt. If anyone could help me I would greatly appreciate it! EDIT: By the way, as soon as I connect, this is what I receive from the server: FF FD 25 FF FB 01 FF FB 03 FF FD 27 FF FD 1F FF FD 00 FF FB 00
modified on Sunday, August 9, 2009 2:28 PM
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Hello Everyone- I am trying to build an application that connects to a telnet server and interacts with it issuing various commands. I have done this in the past and it worked relatively painlessly. This particular device I am working with today however, is using some sort of advanced feature and is sending me an authentication request as soon as I connect to it. (If I use microsoft telnet client to connect, as soon as I connect it prompts me to send my windows login information, if I say no, I am brought to a login: prompt, this is what I want to get to with my program). I have been scouring the net and I cannot find what my response should be to this server to tell it that I do not want to use the NTLM authentication, I just want to be brought to the login: prompt. If anyone could help me I would greatly appreciate it! EDIT: By the way, as soon as I connect, this is what I receive from the server: FF FD 25 FF FB 01 FF FB 03 FF FD 27 FF FD 1F FF FD 00 FF FB 00
modified on Sunday, August 9, 2009 2:28 PM
I am not sure but you might be seeing the Microsoft MS-TNAP protocol: [MS-TNAP]: Telnet: NT LAN Manager (NTLM) Authentication Protocol Specification[^] I am not sure if thats what your seeing though because according to this documentation first byte should be 0xF if authenticating with NTLM 4.1 Telnet Client Successfully Authenticating to a Telnet Server[^] Maybe your seeing something other than NTLM? Hope it helps, -David Delaune
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I am not sure but you might be seeing the Microsoft MS-TNAP protocol: [MS-TNAP]: Telnet: NT LAN Manager (NTLM) Authentication Protocol Specification[^] I am not sure if thats what your seeing though because according to this documentation first byte should be 0xF if authenticating with NTLM 4.1 Telnet Client Successfully Authenticating to a Telnet Server[^] Maybe your seeing something other than NTLM? Hope it helps, -David Delaune
If I use Hyperterminal to connect, it does not ask me if I want to send my username/password when I connect to the server, it simply connects and says Welcome to Microsoft telnet server ... login: I am in need of whatever it is that Hyperterminal is respond to the server after the servers initial response (that appears to be putting it into dumb terminal / TTY mode). I've ran a port sniffer and I'm just not smart enough to figure it out, there is so much data being sent back and forth :(
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If I use Hyperterminal to connect, it does not ask me if I want to send my username/password when I connect to the server, it simply connects and says Welcome to Microsoft telnet server ... login: I am in need of whatever it is that Hyperterminal is respond to the server after the servers initial response (that appears to be putting it into dumb terminal / TTY mode). I've ran a port sniffer and I'm just not smart enough to figure it out, there is so much data being sent back and forth :(
Normally when I program an application, I simply connect to it, send commands to the socket and listen for commands back from the socket. It has always been straightforward. This device however, has something different. When I run the packet sniffer even with Hyperterminal, every command that I send out is proceeded by a ton of hex codes. I've tried to read on the RFC of how telnet works but I am just not that advanced. I'm used to opening the socket, reading and writing to it and that's it. I can't figure out how to get the server to just respond to me with simple ASCII
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Normally when I program an application, I simply connect to it, send commands to the socket and listen for commands back from the socket. It has always been straightforward. This device however, has something different. When I run the packet sniffer even with Hyperterminal, every command that I send out is proceeded by a ton of hex codes. I've tried to read on the RFC of how telnet works but I am just not that advanced. I'm used to opening the socket, reading and writing to it and that's it. I can't figure out how to get the server to just respond to me with simple ASCII
HyperTerminal knowing about telnet protocols shouldn't be too much of a surprise. It even has some settings about Telnet... :)
Luc Pattyn [Forum Guidelines] [My Articles]
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Normally when I program an application, I simply connect to it, send commands to the socket and listen for commands back from the socket. It has always been straightforward. This device however, has something different. When I run the packet sniffer even with Hyperterminal, every command that I send out is proceeded by a ton of hex codes. I've tried to read on the RFC of how telnet works but I am just not that advanced. I'm used to opening the socket, reading and writing to it and that's it. I can't figure out how to get the server to just respond to me with simple ASCII
Have you tried using this third-pary library? .NET Telnet[^] The source code is available here and it seems to handle the negotiation. http://sourceforge.net/projects/dotnettelnet/files/[^] In fact when I look through the source it appears the 0xFF was the IAC WILL TERMINAL-TYPE as decribed in RFC-930[^] Have a look and let me know how it turns out. Good Luck, -David Delaune