Configuring OSPF Network Types in Cisco

Pre-requisites: Open shortest path first (OSPF) router roles and configuration, OSPF network types.

In an OSPF routing domain, there can be multiple OSPF network types that can be configured to manipulate the OSPF operations as per the needs and requirements on a specific interface keeping in mind the network topology and the desired output out of it. To do so, one must know the OSPF network types, difference in them, how to configure them on specific interface after configuring OSPF routing in the topology and which are compatible with one another as. Some network types will work with each other, but you will have to adjust the hello/dead timers. 

Types of OSPF network:

1. Non-broadcast
2. Broadcast
3. Point-to-point
4. Point-to-multipoint
5. Point-to-Multipoint Non-Broadcast
6. Loopback (The default OSPF network type; only available to loopback interfaces)

Interoperate OSPF Network Types:

1. Broadcast to Broadcast
2. Non-broadcast to Non-broadcast
3. Point-to-Point to Point-to-Point
4. Broadcast to Non-broadcast (adjust hello/dead timers)
5. Point-to-Point to Point-to-Multipoint (adjust hello/head timers)

OSPF network type commands:

Interface configuration subcommand	Description
ip ospf network <broadcast | non-broadcast | point-to-multipoint | point-to-point>	Configures an interface OSPF network type to broadcast/non-broadcast/point-to-point/point-to-multipoint (point-to-multipoint -Configures an interface as point-to-multipoint for broadcast media.)
no ip ospf network	To revert the OSPF network type back to its default configuration.
show ip ospf interface [<interface-id>]	To display interface parameters related to OSPF configuration such as network type, router-id, process-id & hello/dead timers.

Configuring OSPF Network Types:

Step 1: Create the 3 router topology in GNS3 as show in the image below :

Step 2: Configure IPv4 address on the physical interface of the routers :

R1(config)#interface FastEthernet0/0
R1(config-if)#ip address 10.1.1.1 255.255.255.0
R1(config-if)#no shutdown
R1(config-if)#interface Serial0/0/0
R1(config-if)#ip address 192.168.1.1 255.255.255.0
R1(config-if)#no shutdown

R2(config)#interface FastEthernet0/0
R2(config-if)#ip address 10.1.1.2 255.255.255.0
R2(config-if)#no shutdown

R3(config-if)#interface Serial0/0/0
R3(config-if)#ip address 192.168.1.2 255.255.255.0
R3(config-if)#no shutdown

Step 3: Configure loopback interfaces on R2 and R3 with IPv4 address :

R2(config)interface Loopback0
R2(config-if)ip address 2.2.2.2 255.255.255.255

R3(config)#interface Loopback0
R3(config-if)#ip address 3.3.3.3 255.255.255.255

Step 3: Configuring OSPF process on all the routers with the command router ospf <process-id> :

R1(config)#router ospf 1
R1(config-router)#exit

R2(config)#router ospf 1
R2(config-router)#exit

R3(config)#router ospf 1
R3(config-router)#exit

Step 4: Enabling OSPF on the interfaces with the interface level sub-command ip ospf <process-id> area <area-id> :

R1(config)#interface FastEthernet0/0
R1(config-if)#ip ospf 1 area 0
R1(config-if)#interface Serial1/0
R1(config-if)#ip ospf 1 area 0

R2(config)#interface FastEthernet0/0
R2(config-if)#ip ospf 1 area 0
R2(config-if)interface Loopback0
R2(config-if)ip ospf 1 area 0

R3(config-if)#interface Serial1/0
R3(config-if)#ip ospf 1 area 0
R3(config-if)interface Loopback0
R3(config-if)ip ospf 1 area 0

Step 5: Verifying interface parameters related to OSPF configuration such as network type, router-id, process-id & hello/dead timers with the show ip ospf interface [<interface-id>] command:

R1#show ip ospf interface

R2#show ip ospf interface

R3#show ip ospf interface

Step 6: Configuring OSPF network type on fast Ethernet links between R1 and R2 :

R1(config)#interface f0/0
R1(config-if)#ip ospf network point-to-point

R2(config)#interface f0/0
R2(config-if)#ip ospf network point-to-point

Step 7: Checking the IPv4 routing table on the routers and seeing OSPF route entry :

R1#show ip route

R2#show ip route

R3#show ip route

Step 8: Checking changes in interface parameters related to OSPF configuration such as network type, hello/dead timers with the show ip ospf interface [<interface-id>] command:

R1#show ip ospf interface

R2#show ip ospf interface

R3#show ip ospf interface

Checking connectivity: 

Ping R3’s loopback interface from R2 and R2’s loopback interface as source:

Simulation:

Ping R2’s loopback interface from R3 and R3’s loopback interface as source:

Simulation: