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primary (Interface for Router)


Hierarchy Level


Configure the primary interface for a device. By default, the multicast-capable interface with the lowest-index address is chosen as the primary interface. If there is no such interface, the point-to-point interface with the lowest-index address is chosen. Otherwise, any interface with an address can be picked. In practice, this means that, on the device, the fxp0 or em0 interface is picked by default. To configure a different interface to be the primary interface, you include this statement.

The primary interface for the router has the following characteristics:

  • It is the interface through which the packets go out when you type a command such as ping—that is, a command that does not include an interface name (there is no interface type-0/0/0.0 qualifier) and where the destination address does not imply any particular outgoing interface.

  • It is the interface on which multicast applications running locally on the router, such as Session Announcement Protocol (SAP), perform group joins by default.

  • It is the interface from which the default local address is derived for packets sourced out of an unnumbered interface if there are no non-127 addresses configured on the loopback interface, lo0.

Required Privilege Level

interface—To view this statement in the configuration.

interface-control—To add this statement to the configuration.

Release Information

Statement introduced before Junos OS Release 7.4.