I have a server running ArchLinux at home called SERVER. Currently, I can gain access to this machine via SSH by issuing
ssh user@SERVER from another computer that is connected on the same LAN. It also works if I replace SERVER with SERVER_LAN_IP (192.168.X.X).
I wanted this server to be publicly accessible from the internet, so I set up my router to forward the appropriate ports (external 1234 to internal 22). Now from a computer on the same LAN, issuing
ssh -p 1234 user@ROUTER_WAN_IP seems to do the trick. However, as soon I leave the LAN, I can't even so much as ping the ROUTER_WAN_IP.
If it helps, I am using a cable internet connection. The router detects the modem through
vlan and gets its external IP via DHCP.