Linux SSH Tunnel – How to Setup SSH Tunnel to Forward SSH

forwardinglinuxsshssh-tunnel

I have computer with Ubuntu behind router that I can't configure. However I want to have ssh access to that computer. I think it is possible with ssh tunneling, but I don't know how to do it. I have another server to which I would like to setup tunneling. How to do it? Or maybe you have some other idea how to solve this problem?

I tried:

ssh -N user@my_server -L 22/localhost/8090

but it says:

bind: Address already in use
channel_setup_fwd_listener: cannot listen to port: 22
Could not request local forwarding.

Best Answer

You are asking it to listen on your local port 22 and forward connections to a remote system's port 8090. You can't do that, because your local port 22 is already taken by your local SSH server.

I think what you are looking for is remote forwarding. Replacing -L 22:localhost:8090 with -R 8090:localhost:22 will tell the remote host to listen on port 8090 and forward requests to your SSH server.

If you are leaving the connection running so you can get in later from a remote site, then you are going to want to make sure the connection doesn't time-out due to inactivity by adding the relevant options (-o TCPKeepAlive=yes or -o ServerAliveInterval=30)

So you'll end up with something like:

ssh -N user@my_server -R 8090:localhost:22 -o ServerAliveInterval=30

Also, if one of the network hops between you and the server is down at any point, the connection will drop despite any KeepAlive options you specify, so you might want to add this command to inittab, or look into the daemontools package or your distro's equivalent , so that it always starts on boot and is restarted when it exits for some reason other then system shutdown (or you could run it from a shell script that loops infinitely, but init or daemontools are cleaner solutions).

Related Solutions

Ubuntu – How to VNC using a SSH Tunnel from one Ubuntu box into another

Enter in all the connection information on the main putty screen. Sounds like you will be using port 443 instead of 22 to connect from the outside. Then go to the Tunnels section and put in 5092 for the Source port. Put in localhost:5900 for the destination. Leave the radio buttons to Local and Auto. Click Add so it shows up in the list and then open up the connection

putty port forward config

When you open up the connection, you will have access to "localhost:5900" from the perspective of the server. You can access it from your local port 5092.

To connect to the server using vnc, plug in localhost:5092 for the host. enter image description here

Ssh – How to automate SSH login with password

Don't use a password. Generate a passphrase-less SSH key and push it to your VM.

If you already have an SSH key, you can skip this step… Just hit Enter for the key and both passphrases:

$ ssh-keygen -t rsa -b 2048
Generating public/private rsa key pair.
Enter file in which to save the key (/home/username/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/username/.ssh/id_rsa.
Your public key has been saved in /home/username/.ssh/id_rsa.pub.

Copy your keys to the target server:

$ ssh-copy-id id@server
id@server's password:

Now try logging into the machine, with ssh 'id@server', and check-in:

.ssh/authorized_keys

Note: If you don't have .ssh dir and authorized_keys file, you need to create it first

to make sure we haven’t added extra keys that you weren’t expecting.

Finally, check to log in…

$ ssh id@server

id@server:~$

You may also want to look into using ssh-agent if you want to try keeping your keys protected with a passphrase.

Best Answer

Related Solutions

Ubuntu – How to VNC using a SSH Tunnel from one Ubuntu box into another

Ssh – How to automate SSH login with password

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