What is the forward_to_host in remote port forwarding? < > Remote port forwarding is created with -R parameter. > > > ssh -R source_port:forward_to_host:destination_port via_host > > > This command connects to via_host. via_host runs a SSH server. It then forwards all connection attempts to source_port on the remote via_host machine to **destination_port port on the local machine (a machine that initiated the ssh command)** . forward_to_host machine must be reachable from the the local machine machine. Forwarding can be also done through Unix sockets. Is `destination_port` port necessary on the machine that initiated the ssh command? Isn't `destination_port` port on machine `forward_to_host` instead? Isn't `forward_to_host` not necessarily the machine that initiated the ssh command? Isn't the only requirement on `forward_to_host` is that it must be any machine reachable from the machine that initiated the ssh command? Thanks.

Unfortunately all the examples in the documentation you link to forward to localhost, and it appears the description of `-R` is restricted to that. You’re correct in thinking that this isn’t an inherent limitation:

* `destination_port` doesn’t have to be on the host where `ssh` is run;
* `destination_port` is indeed on `forward_to_host`;
* `forward_to_host` isn’t necessarily the host where `ssh` is run.



The whole point of `-R` is to allow a remote system to connect to any other system which is reachable from the initiating host. It’s the opposite of `-L`. The target host _can_ be the initiating host itself, but it can also be useful to use this for other hosts — _e.g._ when a reverse tunnel is required for confidentiality, or when the initiating system is inside a network which the remote system can’t access directly.