Configure Default, Primary, and Preferred Addresses and Interfaces

The router has a default address and a primary interface, and interfaces have primary and preferred addresses.

The default address of the router is used as the source address on unnumbered interfaces. The routing protocol process tries to pick the default address as the router ID, which is used by protocols, including OSPF and IBGP.

The primary interface for the router is the interface that packets go out when no interface name is specified and when the destination address does not imply a particular outgoing interface.

An interface's primary address is used by default as the local address for broadcast and multicast packets sourced locally and sent out the interface. An interface's preferred address is the default local address used for packets sourced by the local router to destinations on the subnet.

The default address of the router is chosen using the following sequence:

1. The primary address on the loopback interface lo0 that is not 127.0.0.1 is used.
2. The primary address on the primary interface is used.

To configure these addresses and interfaces, you can do the following:

• Configure the Primary Interface for the Router
• Configure the Primary Address for an Interface
• Configure the Preferred Address for an Interface