Unnumbered interface support for IS-IS with Topology-independent loop-free alternate

You can enable IPv4 processing on a point-to-point interface without assigning it an explicit IPv4 address. The router borrows the IPv4 address of another ethernet or loopback interface already configured on the router and assigns it to the unnumbered interface to conserve IPv4 addresses. To enable IPv4 processing for unnumbered interfaces include unnumbered-address source at the [edit interfaces [name] unit [name] family inet] hierarchy level.