from a technical standpoint, there is several layers to this ARP is how the routers talk at the base layer IP is a secondary layer that provides routing capability having a private IP on a non-routeable address range can still make outbound connections through a router that does have a public routable internet IP address. how it looks internally, if you can connect a PC directly to the outbound-only capable network is your ETH device shows it has no address, but it has a MAC address which is how ARP from the router's PHY can find the path back to send you the responses to your requests