Overview

Logically, to enable IP on an interface, you must assign this interface a unique IP address. Yet, you can borrow an IP address already configured on one of other interfaces on your device instead. This is called "IP unnumbered" and the interface borrowing the IP address is called "IP unnumbered interface".

You can use IP unnumbered to save IP addresses either when available IP addresses are inadequate or when an interface is brought up only for occasional use.