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Configuring Default, Primary, and Preferred Addresses and Interfaces

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

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

The primary interface for the routing platform 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 routing platform to destinations on the subnet.

The default address of the routing platform is chosen using the following sequence:

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

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

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