Configuring an interface

In OSPF, an interface can be configured to act as a connection between a router and one of its attached networks. An interface includes state information that was obtained from underlying lower level protocols and from the routing protocol. An interface to a network is associated with a single IP address and mask. If the address is merely changed, then the OSPF configuration is preserved.

The passive command enables the passive property to and from the OSPF interface where passive interfaces are advertised as OSPF interfaces but do not run the OSPF protocol. By default, only interface addresses that are configured for OSPF are advertised as OSPF interfaces. The passive parameter allows an interface to be advertised as an OSPF interface without running the OSPF protocol. When enabled, the interface ignores ingress OSPF protocol packets and not transmit any OSPF protocol packets.

An interface can be part of more than one area, as specified in RFC5185. To do this, add the keyword secondary when creating the interface.

Use the following syntax to configure an OSPF interface.

ospf ospf-instance
        area area-id
    interface ip-int-name
            advertise-subnet
            authentication-key [authentication-key | hash-key] [hash|hash2]
            authentication-type [password|message-digest]
            dead-interval seconds
            hello-interval seconds
            interface-type {broadcast|point-to-point}
            message-digest-key key-id md5 [key|hash-key][hash|hash2]
            metric metric
            mtu bytes
            passive
            priority number
            retransmit-interval seconds
            no shutdown
            transit-delay seconds

A:ALA-49>config>router>ospf# info
----------------------------------------------
            asbr
            overload
            overload-on-boot timeout 60
            traffic-engineering
            export "OSPF-Export"
            graceful-restart
                helper-disable
            exit
            area 0.0.0.0
                virtual-link 1.2.3.4 transit-area 1.2.3.4
                    hello-interval 9
                    dead-interval 40
                exit
                interface "system"
                exit
            exit
            area 0.0.0.20
                stub
                exit
                interface "to-103"
                exit
            exit
            area 0.0.0.25
                nssa
                exit
            exit
            area 1.2.3.4
            exit 
 area 4.3.2.1
                interface "SR1-3"
                exit
            exit
            area 4.3.2.1
                interface "SR1-3" secondary
                exit
            exit
----------------------------------------------
A:ALA-49>config>router>ospf# area 0.0.0.20