OSPF: Advertising routes on the Interface

The routes can be advertised using the "network" command, but there is also another way. You can do an entire configuration on the Interface Level!

 Cisqueros_R2(config-if)# ip ospf network point-to-point
 Cisqueros_R2(config-if)# ip ospf 1 area 0

*Do not forget to define the "router ospf 1" process in the Global Configuration mode before the interface configuration!

Being defined as a P2P network - DR and BDR election will not take place. The state of all the OSPF Neighbors will be "FULL/-", as presented below:

 Cisqueros_R2#show ip ospf neighbor 

Neighbor ID     Pri   State           Dead Time   Address
3.3.3.3           0   FULL/  -        00:00:30    10.1.23.3
1.1.1.1           0   FULL/  -        00:00:34    10.1.12.1

This way the interface is configured to automatically belong to the Area 0, and the interface Subnet will be "injected" into the OSPF Area.


If there is SECONDARY IP configured on the interface - it will also be advertised. If however you do NOT want to advertise the Secondary IP, you can do the following specific OSPF command:

 Cisqueros_R2(config-if)#ip ospf 1 area 0 secondaries none 

*If you wish the loopback interfaces to be advertised with their correct masks, be sure to configure an OSPF P2P Loopback interface (it makes no difference how you advertise it with the "network" command, you need to also do this)

Cisqueros_R3(config)# int Lo0   
Cisqueros_R3(config-if)# ip ospf network point-to-point