SSH remote port forwarding

The problem: when you set up SSH remote port forwarding, for example

or, put another way,

ssh user@front-server -R "0.0.0.0:12345:local-env-server:12345" -NCv

the listening port (12345 in our example) is bound to 127.0.0.1 (checked on Ubuntu 18.04 and CentOS 6/7), which in turn makes outside connections impossible:

~# netstat -tan|grep 12345
tcp        0      0 127.0.0.1:12345          0.0.0.0:*               LISTEN

The fix:

1. Set in /etc/ssh/sshd_config:

   GatewayPorts clientspecified
   

2. Restart sshd:

   ~# systemctl restart sshd
   

After that all is well:

~# netstat -tan|grep 12345
tcp        0      0 0.0.0.0:12345          0.0.0.0:*               LISTEN

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Originally published in Russian on LiveJournal.