Sometimes you want to directly access a server on a remote LAN beyond a firewall and you don’t want to set up a VPN, or maybe you want to encrypt an unencrypted service in simple and easy way. If you can contact a [remote] SSH server, then you only need a ssh client, and that’s all!
Let’s see it more in deep:
ssh -fn -N -L 1080:remote_www.server.com:80 root@remote-ssh-proxy.server.com
The -N -L switches do the trick! The first parameter to the L siwtch (1080 in this example) will be the local port you will use to direct connect to the remote service, located at remote_www.server.com address on port 80. So, for example, you can point your browser to http://localhost:1080 and magically you will have established an encrypted connection to that web server (well, if you have a user/password for remote-ssh-prxy ;)
The -N switch is mandatory in this use case because it will disable the need of a program to be passed as an argument to ssh, permitting the tunnel-only connection.
The -fn is to put in background the connection, so the tunnel will stay open and your console won’t be blocked.
You can change the -L for -R which will do just the reverse. It will forward a port from the remote proxy to a local machine.
The eternal fight between admins and computers 