Here’s a little tip on how to tunnel ssh through another machine with the
-L option. While not terribly difficult, I did spend some time figuring this out…Maybe this will save someone else some time ;-)
The network setup at work (simplified):
Code:
[ Workstation ]
|
|
[ Firewall ]
|
|
~ The Internet ~
|
|
[Public webserver]
The problem is connecting to public webserver from my workstation, I had to first ssh or sftp to the Linux firewall, and from that to the webserver.
There has to be an easier way … And a look at the SSH manpage provided the answer: The
-L option.
Excerpt from From
ssh(1):
Code:
-L [bind_address:]port:host:hostport
Specifies that the given port on the local (client) host is to be
forwarded to the given host and port on the remote side. This
works by allocating a socket to listen to port on the local side,
optionally bound to the specified bind_address.
Let me just give you an example on how to create the tunnel:
Code:
$ ssh -f -N -p 22 username@firewall -L 2844/webserver.example.com/22
To briefly explain what the other options mean:
- -f Runs the tunnel in the background.
- -N Don't execute a login command, just setup the tunnel.
- -p Connect to the firewall on port 22
You can now connect with ssh, sftp, or scp though
localhost:2844
Code:
$ ssh -p 2844 myusername@localhost
$ scp -P 2844 file.tar.gz myusername@localhost:file.tar.gz
Note that
ssh(1) requires
-p and
scp(1) -P.
Testing
For debugging, don’t forget you can specify
-v up to three times to get more information about what’s going on. In addition, it’s probably best to test with
telnet since this excludes things like authentication problems.
Code:
$ telnet localhost 2844
Trying ::1...
Connected to localhost.
Escape character is '^]'.
SSH-2.0-OpenSSH_5.1p1 FreeBSD-20080901
If you don’t see the last line, something is wrong.
Bonus tip
As a free complimentary bonus tip, it’s also very easy to setup a convenient shortcut in
~/.ssh/config
Code:
Host webserver
Hostname localhost
Port 2844
User myusername
Further reading
ssh(1)
ssh_config(5)