How does port 80 open on gray IPs?

Question

Computer networks

What determines the openness of port 80 on a gray IP? Sometimes it opens the page of my router if I register an external Ip with port 80, and sometimes not, only through 192.168.0.1. Why and how does it work?

Answer 1

Gray IP is not routed to the external network (read the Internet), respectively, it can only be opened from the local network.
What external IP do you specify that the router opens?