Telnet To UNIX Server

Hi Everybody,

I'm trying to TELNET to a UNIX server from within my VB .NET proggy.

I can connect up to the server on Port 23, no problem, using a Socket.

My problem is sending commands to the Socket and receiving anything intelligible back.

The only data I'm able to get back from the server is the string below:-

"}} }#}}'}$

This happens on the first pass of the code. If I then disconnect the socket, close it and re-open it, all I get back is an empty string!

Here's the code I'm using (I have never used Sockets before btw!).

VB Code:

Imports System.Net
Imports System.Net.Sockets
Imports System.Text
 
Class UNIX_Connection
 
Public mySocket As Socket
Public IP As IPEndPoint
Public Connected As Boolean
 
Public Sub Connect(ByVal Server As String)
 
IP = New IPEndPoint(Dns.GetHostByName(Server).AddressList(0), 23)
mySocket = New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)
Try
mySocket.Connect(IP)
Connected = True
Catch ex As Exception
Connected = False
End Try
 
End Sub
 
Public Sub SendData(ByVal Message As String)
 
If Connected = False Then
MessageBox.Show("No connection exists.")
Exit Sub
End If
 
Dim Buffer() As Byte = ASCIIEncoding.ASCII.GetBytes(Message)
mySocket.Send(Buffer, Buffer.Length, SocketFlags.None)
 
Dim ReceivedData(255) As Byte
mySocket.Receive(ReceivedData, 0, mySocket.Available, SocketFlags.None)
 
MessageBox.Show(ASCIIEncoding.ASCII.GetString(ReceivedData))
 
End Sub
 
Public Sub Disconnect()
 
mySocket.Shutdown(SocketShutdown.Both)
mySocket.Close()
Connected = False
 
End Sub
 
End Class

Any help would be fantastic.

Yes. I am getting the same thing in VB5 and .NET

It works fine for telnetting to a Cisco firewall for administation of it. BUT when connecting to a unix box or IBM mainframe you get rubbish back despite both of these working with DOS telnet.

I suspect that a string has to be sent to tell the other end what type of terminal you are running (VT100 VT320 etc).

I don't know for sure but next week I will get my LAN analyser out and capture what DOS does when it connects.

had a look.

its not just rubbish you are getting.

the server sends FF FD xx (where xx is a hex character)

If you prefer it sends chr(255)+chr(253)+chr(?)

the 255 means "interpret as command"
the 253 means "suboption negotiate DO"

the ? means various options EG. x18 = terminal type

I managed to get a login prompt from an IBM mainframe by sending:

chr(255)+chr(252)+chr(?) in response to each request to negotiate which basic means WONT negotiate the option.