Single area OSPF configuration

Single-area OSPFv2 configuration

Configuration

• router ospf process-id
• The process-id value represents a number between 1 and 65,535
• The process-id is locally significant, it does not have to the same on the other routers
• But it is best practice to use the same process-id on all OSPF routers

Router-IDs

• An OSPF router ID is a 32-bit value, represented as IPv4 address.
• The router ID is used to uniquely identify an OSPF router.
• All OSPF packets include the router ID of the originating router.
• The router ID can be defined by administrator or automatically assigned by the router
• The router ID is used by an OSPF-enabled router
  • Participate in the synchronization of OSPF databases
    • During the ExChange State, the router with the highest router ID will send the database decriptor(DBD) packet first
  • Participate in the election of the designated router(DR)
    • The router with the highest router ID is elected the DR
    • The router with the second router ID is elected the BDR

Router-ID Determination

1. OSPF router-id rid (This is the recommended method to assign a router ID)
2. If the router ID is not configured, the router chooses the highest IPv4 address of any configured loopback interface.
3. If no loopback interfaces are configured, the router chooses the highest active IPv4 address of any of its physical interfaces.

Modify Router ID

• After a router selects a router ID, an active OSPF router does not allow the router ID to be changed until the router is reloaded or the OSPF process is reset.
• Rest the OSPF process clear ip ospf process

Configure OSPF directly on the interface

• routers(config-if)# ip ospf process-id area area-id

Passive Interface

• To prevent the transmission of routing messages through a router interface
• passive-interface interface

Change the network type

• router(config-if)# ip ospf network point-to-point/ broadcast
• In the point-to-point network, the election of DR and BDR is not conducted.