How to configure open shortest path first routing protocol

In this article I will demonstrate an example of OSPF Routing configuration. We will use four different series router so you can get familiar with all different platform covered in CCNA exam. Create a topology as shown in figure.

1841 Series Router0 (R1)
	FastEthernet0/0	Serial0/0/0
IP address	10.0.0.1	20.0.0.1
Connected With	Pc0	R2 on Serial 0/0
2811 Series Router0 (R4)
	FastEthernet0/0	Serial0/0/0
IP address	50.0.0.1	40.0.0.2
Connected With	Pc1	R3 on Serial 0/0

2621XM Series Router0 (R3)
		FastEthernet0/0	Serial0/0/0
IP address		30.0.0.2	40.0.0.1
Connected With		FastEthernet0/0	R4 on Serial 0/0/0
2620XM Series Router1 (R2)
	FastEthernet0/0			Serial0/0
IP address	30.0.0.1			20.0.0.2
Connected With	R3 on FastEthernet0/0			R1 on Serial 0/0/0

PC-PT PC0
	FastEthernet0	Default Gateway
IP address	10.0.0.2	10.0.0.1
Connected With	R1 on FastEthernet0/0
PC-PT PC1
	FastEthernet0	Default Gateway
IP address	50.0.0.2	50.0.0.1
Connected With	R4 on FastEthernet0/0

Configuring OSPF is slightly different from configuring RIP. When configuring OSPF, use the following syntax:

Router(config)# router ospf process_ID

Router(config-router)# network IP_address wildcard_mask area area_#

The process_ID is locally significant and is used to differentiate between OSPF processes running on the same router. Your router might be a boundary router between two OSPF autonomous systems, and to differentiate them on your router, you will give them unique process IDs. Note that these numbers do not need to match between different routers so they have nothing to do with autonomous system numbers.

To configure any router double click on it and select CLI.To configure this topology use this step by step guide.

(1841Router0) Hostname R1

To configure and enable ospf routing on R1 follow these commands exactly.

Router>enable

Router#configure terminal

Enter configuration commands, one per line.  End with CNTL/Z.

Router(config)#hostname R1

R1(config)#interface fastethernet 0/0

R1(config-if)#ip address 10.0.0.1 255.0.0.0

R1(config-if)#no shutdown

%LINK-5-CHANGED: Interface FastEthernet0/0, changed state to up

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up

R1(config-if)#exit

R1(config)#interface serial 0/0/0

R1(config-if)#ip address 20.0.0.1 255.0.0.0

R1(config-if)#clock rate 64000

R1(config-if)#bandwidth 64

R1(config-if)#no shutdown

%LINK-5-CHANGED: Interface Serial0/0/0, changed state to down

R1(config-if)#exit

%LINK-5-CHANGED: Interface Serial0/0/0, changed state to up

R1(config)#router ospf 1

R1(config-router)#network 10.0.0.0 0.255.255.255 area 0

R1(config-router)#network 20.0.0.0 0.255.255.255 area 0

R1(config-router)#exit

R1(config)#

(2620XM-Router1) Hostname R2

To configure and enable ospf routing on R2 follow these commands exactly.

Router>enable

Router#configure terminal

Enter configuration commands, one per line.  End with CNTL/Z.

Router(config)#hostname R2

R2(config)#interface serial 0/0

R2(config-if)#ip address 20.0.0.2 255.0.0.0

R2(config-if)#no shutdown

%LINK-5-CHANGED: Interface Serial0/0, changed state to up

%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0, changed state to up

R2(config-if)#exit

R2(config)#interface fastethernet 0/0

R2(config-if)#ip address 30.0.0.1 255.0.0.0

R2(config-if)#no shutdown

%LINK-5-CHANGED: Interface FastEthernet0/0, changed state to up

R2(config-if)#exit

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up

R2(config)#router ospf 2

R2(config-router)#network 20.0.0.0 0.255.255.255 area 0

R2(config-router)#network 3

00:03:10: %OSPF-5-ADJCHG: Process 2, Nbr 20.0.0.1 on Serial0/0 from

 LOADING to FULL, Loading Done0.0.0.0 0.255.255.255 area 0

R2(config-router)#network 30.0.0.0 0.255.255.255 area 0

R2(config-router)#exit

R2(config)#

(2620XM-Router2)Hostname R3

To configure and enable ospf routing on R3 follow these commands exactly.

Router>enable

Router#configure terminal

Enter configuration commands, one per line.  End with CNTL/Z.

Router(config)#hostname R3

R3(config)#interface fastethernet 0/0

R3(config-if)#ip address 30.0.0.2 255.0.0.0

R3(config-if)#no shutdown

%LINK-5-CHANGED: Interface FastEthernet0/0, changed state to up

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up

R3(config-if)#interface serial 0/0

R3(config-if)#ip address 40.0.0.1 255.0.0.0

R3(config-if)#clock rate 64000

R3(config-if)#bandwidth 64

R3(config-if)#no shutdown

%LINK-5-CHANGED: Interface Serial0/0, changed state to down

R3(config-if)#exit

%LINK-5-CHANGED: Interface Serial0/0, changed state to up

%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0, changed state to up

R3(config)#router ospf 3

R3(config-router)#network 40.0.0.0 0.255.255.255 area 0

R3(config-router)#network 30.0.0.0 0.255.255.255 area 0

00:04:53: %OSPF-5-ADJCHG: Process 3, Nbr 30.0.0.1 on FastEthernet0/0 from

 LOADING to FULL, Loading D

R3(config-router)#exit

R3(config)#

%SYS-5-CONFIG_I: Configured from console by console

R3#

(2811Router3) Hostname R4

To configure and enable ospf routing on R4 follow these commands exactly.

Router>enable

Router#configure terminal

Enter configuration commands, one per line.  End with CNTL/Z.

Router(config)#interface serial 0/0/0

Router(config-if)#ip address 40.0.0.2 255.0.0.0

Router(config-if)#no shutdown

%LINK-5-CHANGED: Interface Serial0/0/0, changed state to up

%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0/0, changed state to up

Router(config-if)#exit

Router(config)#interface fastethernet 0/0

Router(config-if)#ip address 50.0.0.1 255.0.0.0

Router(config-if)#no shutdown

%LINK-5-CHANGED: Interface FastEthernet0/0, changed state to up

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up

Router(config-if)#exit

R4(config)#router ospf 4

R4(config-router)#network 50.0.0.0 0.255.255.255 area 0

R4(config-router)#network 40.0.0.0 0.255.255.255 area 0

R4(config-router)#

00:06:32: %OSPF-5-ADJCHG: Process 4, Nbr 40.0.0.1 on Serial0/0/0 from

LOADING to FULL, Loading Done

R4(config-router)#exit

R4(config)#

PC-1

PC>ipconfig

IP Address......................: 10.0.0.2

Subnet Mask.....................: 255.0.0.0

Default Gateway.................: 10.0.0.1

PC>ping 50.0.0.2

Pinging 50.0.0.2 with 32 bytes of data:

Reply from 50.0.0.2: bytes=32 time=156ms TTL=124

Reply from 50.0.0.2: bytes=32 time=127ms TTL=124

Reply from 50.0.0.2: bytes=32 time=156ms TTL=124

Reply from 50.0.0.2: bytes=32 time=140ms TTL=124

Ping statistics for 50.0.0.2:

    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),

Approximate round trip times in milli-seconds:

    Minimum = 127ms, Maximum = 156ms, Average = 144ms

PC>

PC-2

PC>ipconfig

IP Address......................: 50.0.0.2

Subnet Mask.....................: 255.0.0.0

Default Gateway.................: 50.0.0.1

PC>ping 10.0.0.2

Pinging 10.0.0.2 with 32 bytes of data:

Reply from 10.0.0.2: bytes=32 time=140ms TTL=124

Reply from 10.0.0.2: bytes=32 time=141ms TTL=124

Reply from 10.0.0.2: bytes=32 time=157ms TTL=124

Reply from 10.0.0.2: bytes=32 time=156ms TTL=124

Ping statistics for 10.0.0.2:

    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),

Approximate round trip times in milli-seconds:

    Minimum = 140ms, Maximum = 157ms, Average = 148ms

You can verify that ospf is running successfully via show ip protocols command in privilege mode.

R4#show ip protocols

Routing Protocol is "ospf 4"

  Outgoing update filter list for all interfaces is not set

  Incoming update filter list for all interfaces is not set

  Router ID 50.0.0.1

  Number of areas in this router is 1. 1 normal 0 stub 0 nssa

  Maximum path: 4

  Routing for Networks:

    50.0.0.0 0.255.255.255 area 0

    40.0.0.0 0.255.255.255 area 0

  Routing Information Sources:

    Gateway         Distance      Last Update

    40.0.0.1             110      00:01:26

  Distance: (default is 110)

R4#

You can use show ip oute command to troubleshoot ospf network. If you did not see information about any route checks the router attached with that network.

R4#show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP

       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

       * - candidate default, U - per-user static route, o - ODR

       P - periodic downloaded static route

Gateway of last resort is not set

O    10.0.0.0/8 [110/1564] via 40.0.0.1, 00:02:37, Serial0/0/0

O    20.0.0.0/8 [110/1563] via 40.0.0.1, 00:02:37, Serial0/0/0

O    30.0.0.0/8 [110/782] via 40.0.0.1, 00:02:37, Serial0/0/0

C    40.0.0.0/8 is directly connected, Serial0/0/0

C    50.0.0.0/8 is directly connected, FastEthernet0/0

R4#

To test ospf routing do ping from pc1 to pc2 and vice versa. If you get replay then you have successfully configured ospf routing but if you did not get replay double check this configuration and try to troubleshoot. I have uploaded a configured and tested topology in case you are unable to locate the problem spot then download this configuration file. And try to find out where have you committed mistake

ospf routing configurations

Configuration command of OSPF

Commands	Descriptions
Router(config)#router ospf 1	Starts OSPF process 1. The process ID is any positive integer value between 1 and 65,535.
Router(config-router)#network 172.16.0.0 0.0.255.255 area 0	OSPF advertises interfaces, not networks. Uses the wildcard mask to determine which interfaces to advertise.
Router(config-if)#ip ospf hellointerval timer 20	Changes the Hello Interval timer to 20 seconds.
Router(config-if)#ip ospf deadinterval 80	Changes the Dead Interval timer to 80 seconds.
NOTE: Hello and Dead Interval timers must match for routers to become neighbors
Router#show ip protocol	Displays parameters for all protocols running on the router
Router#show ip route	Displays a complete IP routing table
Router#show ip ospf	Displays basic information about OSPF routing processes
Router#show ip ospf interface	Displays OSPF info as it relates to all interfaces
Router#show ip ospf interface fastethernet 0/0	Displays OSPF information for interface fastethernet 0/0
Router#show ip ospf border-routers	Displays border and boundary router information
Router#show ip ospf neighbor	Lists all OSPF neighbors and their states
Router#show ip ospf neighbor detail	Displays a detailed list of neighbors
Router#clear ip route *	Clears entire routing table, forcing it to rebuild
Router#clear ip route a.b.c.d	Clears specific route to network a.b.c.d
Router#clear ip opsf counters	Resets OSPF counters
Router#clear ip ospf process	Resets entire OSPF process, forcing OSPF to re-create neighbors, database, and routing table
Router#debug ip ospf events	Displays all OSPF events
Router#debug ip ospf adjacency	Displays various OSPF states and DR/ BDR election between adjacent routers
Router#debug ip ospf packets	Displays OPSF packets