ssh telnet emulator – How to Emulate Telnet Over SSH

emulatorsshtelnet

I have a client/server application that work over a telnet connection, and it does not support SSH. Basically the client opens a telnet connection to the server, which starts a specific shell, and the client sends commands over the telnet connection to that shell. The problem is that I need to make this work over a ssh connection, and the remote server does not have telnet services, so I cannot use a tunnel over the ssh connection. I need some kind of telnet emulator that will offer a telnet endpoint to the client, while connecting through ssh to the server. Is there any way to do this?

thanks

Best Answer

That's a normal case for port forwarding over ssh.

A server <ip> has ssh endpoint opened and an application server listening on Telnet port 23.

A client has an application client which should connect to <ip>:23. Also client has nothing listening on port 23.

Let's establish port forwarding from server to client:

ssh -N -L 23:127.0.0.1:23 user@<ip> >/dev/null 2>&1 &

Here we:

  • connect to the server <ip> as user user;
  • put ssh session into background;
  • redirect ssh session's output into /dev/null to avoid any messages on console;
  • forward port 23 from the server's localhost to the client (your application server should listen on all IP interfaces, including 127.0.0.1)

Now application client should connect to the address 127.0.0.1:23 to work with the application server.

Update

As per explanations, we have a telnet only capable client software and ssh only capable server. And client should be able to access the server.

As it happens, such solution does exist. From manual:

SSH/Telnet gateway

In the Telnet-DeleGate (DeleGate server for Telnet clients), a host name prefixed with "-ssh" and "." (as "-ssh.host") implies a SSH server on the host. In access to such a server, Telnet-DeleGate works as a gateway between the SSH server and a Telnet client. For example, using a Telnet-DeleGate configured like follows, Telnet clients can login to a SSH server on host as user as follows:

% delegated -P8023 SERVER=telnet://-ssh
% telnet -l user@host localhost 8023

Meet DeleGate

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