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7.5 OSPF interface

Interface Command: ip ospf area AREA [ADDR]
Interface Command: no ip ospf area [ADDR]

Enable OSPF on the interface, optionally restricted to just the IP address given by ADDR, putting it in the AREA area. Per interface area settings take precedence to network commands (see OSPF network command).

If you have a lot of interfaces, and/or a lot of subnets, then enabling OSPF via this command may result in a slight performance improvement.

Interface Command: ip ospf authentication-key AUTH_KEY
Interface Command: no ip ospf authentication-key

Set OSPF authentication key to a simple password. After setting AUTH_KEY, all OSPF packets are authenticated. AUTH_KEY has length up to 8 chars.

Simple text password authentication is insecure and deprecated in favour of MD5 HMAC authentication (see ip ospf authentication message-digest).

Interface Command: ip ospf authentication message-digest

Specify that MD5 HMAC authentication must be used on this interface. MD5 keying material must also be configured (see ip ospf message-digest-key). Overrides any authentication enabled on a per-area basis (see area authentication message-digest).

Note that OSPF MD5 authentication requires that time never go backwards (correct time is NOT important, only that it never goes backwards), even across resets, if ospfd is to be able to promptly reestabish adjacencies with its neighbours after restarts/reboots. The host should have system time be set at boot from an external or non-volatile source (eg battery backed clock, NTP, etc.) or else the system clock should be periodically saved to non-volative storage and restored at boot if MD5 authentication is to be expected to work reliably.

Interface Command: ip ospf message-digest-key KEYID md5 KEY
Interface Command: no ip ospf message-digest-key

Set OSPF authentication key to a cryptographic password. The cryptographic algorithm is MD5.

KEYID identifies secret key used to create the message digest. This ID is part of the protocol and must be consistent across routers on a link.

KEY is the actual message digest key, of up to 16 chars (larger strings will be truncated), and is associated with the given KEYID.

Interface Command: ip ospf cost <1-65535>
Interface Command: no ip ospf cost

Set link cost for the specified interface. The cost value is set to router-LSA’s metric field and used for SPF calculation.

Interface Command: ip ospf dead-interval <1-65535>
Interface Command: ip ospf dead-interval minimal hello-multiplier <2-20>
Interface Command: no ip ospf dead-interval

Set number of seconds for RouterDeadInterval timer value used for Wait Timer and Inactivity Timer. This value must be the same for all routers attached to a common network. The default value is 40 seconds.

If ’minimal’ is specified instead, then the dead-interval is set to 1 second and one must specify a hello-multiplier. The hello-multiplier specifies how many Hellos to send per second, from 2 (every 500ms) to 20 (every 50ms). Thus one can have 1s convergence time for OSPF. If this form is specified, then the hello-interval advertised in Hello packets is set to 0 and the hello-interval on received Hello packets is not checked, thus the hello-multiplier need NOT be the same across multiple routers on a common link.

Interface Command: ip ospf hello-interval <1-65535>
Interface Command: no ip ospf hello-interval

Set number of seconds for HelloInterval timer value. Setting this value, Hello packet will be sent every timer value seconds on the specified interface. This value must be the same for all routers attached to a common network. The default value is 10 seconds.

This command has no effect if ip ospf dead-interval minimal is also specified for the interface.

Interface Command: ip ospf network (broadcast|non-broadcast|point-to-multipoint|point-to-point)
Interface Command: no ip ospf network

Set explicitly network type for specifed interface.

Interface Command: ip ospf priority <0-255>
Interface Command: no ip ospf priority

Set RouterPriority integer value. The router with the highest priority will be more eligible to become Designated Router. Setting the value to 0, makes the router ineligible to become Designated Router. The default value is 1.

Interface Command: ip ospf retransmit-interval <1-65535>
Interface Command: no ip ospf retransmit interval

Set number of seconds for RxmtInterval timer value. This value is used when retransmitting Database Description and Link State Request packets. The default value is 5 seconds.

Interface Command: ip ospf transmit-delay
Interface Command: no ip ospf transmit-delay

Set number of seconds for InfTransDelay value. LSAs’ age should be incremented by this value when transmitting. The default value is 1 seconds.


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