The Internet is running out of IP addresses (ipv4, but years after ipv6 came out we still haven't switched over to it). This is realer than Peak Oil. And so most of us are connected to the Internet with an IP address shared with many other people, with many devices seen by the outside world as having one address.
But more locally, behind a router or gateway or firewall, we all have unique addresses and names to identify each other by. But only locally.
And so each of our devices have two or more possible IP addresses. Each computer should have a local IP address, its main...