Connection with no open ports on both sides

[rik_rs]

I use SSVNC on Debian with the option -listen to accept reverse connection from SC clients. This way the clients don't have to open any ports.
100% all good and working.
The problem arises when I'm out of the office with a smarphone + tethering and I have to accept a reverse connection. In such case there is no way to open a port and that's a big problem!

I thought: no problem! I have a server in the office so I can make a tunnel so that instead of
ScClient:5900-->5900:router:5900-->PC:5900->ssvnc:5900
I could solve the problem with

Code: Select all

ssh -4 -L 5900:localhost:5900 -N user@host

and the chain becomes
ScClient:5900-->5900:router:5900-->Server:5900<--sshPC:5900<--ssvnc:5900

Unfortunately it doesn't work and I can't figure out why. The only possible problem I see is that when the tunnel is active, SSVNC shows this info
ListenAtTcpPort: bind: Address already in use
vncviewer -listen: listening on port 5900 ipv4_fd: -1 ipv6_fd: 4
If i close the tunnel and run ssvnc again, the first line is not present and the 2nd one says
vncviewer -listen: listening on port 5900 ipv4_fd: 4 ipv6_fd: 5

Any help?