ssh port forwarding (tunneling) in linux
laptop -> gateway -> remote_server_1

laptop -> remote_server_2

mylaptop$ ssh -L 3001:localhost:3000 server_2
server_2$ netcat -l 3000

ssh -t -t -L 3003:server_1:22 gateway

ssh -R 3002:localhost:3001 -p3003 localhost
echo "bar" | nc localhost 3002`

mylaptop$ ssh -L 3001:localhost:3000 server_2
server_2$ netcat -l 3000

mylaptop$ ssh -R 3002:localhost:3001 server_1
server_1$ echo "foo" | netcat localhost 3002