This read-write address is the unicast routable address assigned to the mobile node as its permanent home address for mobile-IP purposes. An admin configures this so the device has a stable, carrier/network-recognized identity that mobile-IP registration and reachability can be built around, regardless of which foreign network the device is currently attached to. For example, a router that roams across different coverage areas keeps this fixed home address so that mobile-IP correspondents can always reach it through the home agent, regardless of its current attachment point.