ssh tunneling and port forwarding

###Single hop tunelling:

ssh -f -N -L 9906:127.0.0.1:3306 [email protected]

where,

-f puts ssh in background
-N makes it not execute a remote command

This will forward all local port 9906 traffic to port 3306 on the remote dev.example.com server

###Multi-Hop Tunelling:

Tunnel from localhost to host1 and from host1 to host2:

ssh -L 9999:localhost:9999 host1 ssh -L 9999:localhost:1234 -N host2

This will open a tunnel from localhost to host1 and another tunnel from host1 to host2. However the port 9999 to host2:1234 can be used by anyone on host1. This may or may not be a problem.

Another Example:

Assume you have you have a web server running on 10.1.0.93 in a private network on port 80 which is reachable by a gateway server 198.1.1.34, here is how to open the ssh tunnel:

ssh -L 80:localhost:80 [email protected] -t ssh -L 80:localhost:80 [email protected]

Example SSH Config:

Host cwg
  HostName 198.0.218.179
  Port 22
  User root
  IdentityFile ~/.ssh/id_rsa

# Access cw sync on localhost:9292
# Enable: ssh -f -N cw_tunnel
Host cw_tunnel
  HostName 198.0.218.179
  User root
  IdentityFile ~/.ssh/id_rsa
  LocalForward 9292 127.0.0.1:9292

# auto tunelling to securehost (remote host) via jumphost (gateway)
# we tell ssh that when it establishes a connection to securehost to do so using
# the stdin/stdout of the ProxyCommand as a transport. The ProxyCommand then tells
# the system to first ssh to our bastion host and open a netcat connection to host
# %h (hostname supplied to ssh) on port %p (port supplied to ssh).
Host jumphost
  ProxyCommand none
Host securehost
  ProxyCommand ssh jumphost -W %h:%p

slgithub/ssh_tunneling.md