I am struggling with understanding if and how the following is possible.Say that I have a machine T (target) which I want to access from remote (ideally via ssh).T is behind a router/firewall R and I cannot forward port (e.g.) 22 of R to port 22  of T. In a word, no direct ssh access to T is possible.Now say that I have a machine A on which I have full control. I can ssh from T to A, i.e.  T:  ssh user@Asucceeds.Q1: can I use this to access shell of T from A? I.e., can I use the connection created from T to A, to use T from A?   T ---> ssh ----> A          # this is possible                  T <--- ? shell ? <---- A    # is this possible?Q2: If Q1 is possible:Let's say that I have a third machine L (e.g. my laptop), and I aim at having access to the shell of T from L. Can I ssh-tunnel A access to L?   T ----> ssh ----> A <---- ssh < ---- L   T <-------  ?? %& ?? <------- L       # is this possible?any help appreciated.
Having ssh tunneling itself for remote access from a third machine
ssh;ssh tunneling
This is of course possible. Q1: reverse tunneling over ssh is possible ?Yes.Here are some answers about reserve tunneling:(UL) How does reverse SSH tunneling work?(UL) SFTP over reverse SSH tunnel?Q2: tunneling a reserved tunnel is possible ?Yes, this is basically an ssh tunnel over a tunnel. Here are a few answers regarding tunnel into a tunnel:(UL) Tunnel traffic through another machine over ssh(UL) log into a machine through another(UL) How to put a tunnel in a tunnel?