This read-write IpAddress specifies, per its source description, the source address this system uses for RIP traffic on this interface, which for a numbered interface must match the interface's own IP address, or for an unnumbered interface must match some other interface's address on the system. Admins on an unnumbered interface (e.g., certain WAN links) must explicitly configure this to a valid address elsewhere on the router, since the interface itself has no IP of its own to use. For example, an unnumbered WAN interface would have this set to the router's loopback or LAN interface address so RIP updates sent out that link carry a consistent, reachable source address.