SSH

Local port forwarding

ssh -L $lport:$dhost:$dport $user@$sshserver

Remote port forwarding

ssh -R $rport:$dhost:$lport $user@$sshserver

B:1 -> A:2 <- C:3  <---> internet

NOTE: this option can be useless if you have no root access to change the sshd_config file in the machine A, and restart the ssh service, since you need to set GatewayPorts yes in order to let others than the ssh server machine could access to dhost. However, there's a workaround: Remote Port Forwarding from B:port1 to one remote server A:port2 and then a Local Port Forwarding to the same A:port2 machine using a local machine C:port3 to which you have more access. You can know access to the service in B:port1 using C:port3.

Dynamic port forwarding

ssh -D $lport $user@$server