Requirements

• GNS3
• Cisco IOS image(c3725-adventerprisek9-mz.124-15.T5 in this example)

Topology

PC Setting

On PC1

PC1(config)#no ip routing
PC1(config)#ip default-gateway 192.168.1.254
PC1(config)#interface fastEthernet 0/0
PC1(config-if)#ip address 192.168.1.1 255.255.255.0
PC1(config-if)#no shutdown
PC1(config-if)#exit

PC2(config)#no ip routing
PC2(config)#ip default-gateway 192.168.2.254
PC2(config)#interface fastEthernet 0/0
PC2(config-if)#ip address 192.168.2.1 255.255.255.0
PC2(config-if)#no shutdown
PC2(config-if)#exit

Router Setting

First, configure interface for each router On R1

R1(config)#interface serial 1/0
R1(config-if)#ip address 192.168.12.1 255.255.255.0
R1(config-if)#no shutdown
R1(config-if)#exit

R1(config)#interface fastEthernet 0/0
R1(config-if)#ip address 192.168.1.254 255.255.255.0
R1(config-if)#no shutdown
R1(config-if)#exit

R1(config)#interface loopback 0
R1(config-if)#ip address 1.1.1.1 255.255.255.255
R1(config-if)#exit

On R2

R2(config)#interface serial 1/0
R2(config-if)#clock rate 64000
R2(config-if)#ip address 192.168.12.2 255.255.255.0
R2(config-if)#no shutdown
R2(config-if)#exit

R2(config)#interface serial 1/1
R2(config-if)#clock rate 64000
R2(config-if)#ip address 192.168.23.2 255.255.255.0
R2(config-if)#no shutdown
R2(config-if)#exit

R2(config-router)#interface loopback 0
R2(config-if)#ip address 2.2.2.2 255.255.255.255
R2(config-if)#exit

On R3

R3(config)#interface serial 1/0
R3(config-if)#ip address 192.168.23.3 255.255.255.0
R3(config-if)#no shutdown
R3(config-if)#exit

R3(config)#interface fastEthernet 0/0
R3(config-if)#ip address 192.168.2.254 255.255.255.0
R3(config-if)#no shutdown
R3(config-if)#exit

R3(config)#interface loopback 0
R3(config-if)#ip address 3.3.3.3 255.255.255.255
R3(config-if)#exit

Then, apply single area OSPF

On R1

R1(config)#router ospf 1
R1(config-router)#router-id 1.1.1.1
R1(config-router)#network 192.168.1.0 0.0.0.255 area 0
R1(config-router)#network 192.168.12.0 0.0.0.255 area 0
R1(config-router)#exit

On R2

R2(config)#router ospf 1
R2(config-router)#router-id 2.2.2.2
R2(config-router)#network 192.168.12.0 0.0.0.255 area 0
R2(config-router)#network 192.168.23.0 0.0.0.255 area 0
R1(config-router)#exit

On R3

R3(config)#router ospf 1
R3(config-router)#router-id 3.3.3.3
R3(config-router)#network 192.168.23.0 0.0.0.255 area 0
R3(config-router)#network 192.168.2.0 0.0.0.255 area 0
R3(config-router)#exit

Check OSPF interface

Take R1 as an example

R1#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
2.2.2.2           0   FULL/  -        00:00:37    192.168.12.2    Serial1/0

R1#show ip ospf interface
Serial1/0 is up, line protocol is up
  Internet Address 192.168.12.1/24, Area 0
  Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 64
  Transmit Delay is 1 sec, State POINT_TO_POINT
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    oob-resync timeout 40
    Hello due in 00:00:00
  Supports Link-local Signaling (LLS)
  Cisco NSF helper support enabled
  IETF NSF helper support enabled
  Index 2/2, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 1
  Last flood scan time is 0 msec, maximum is 0 msec
  Neighbor Count is 1, Adjacent neighbor count is 1
    Adjacent with neighbor 2.2.2.2
  Suppress hello for 0 neighbor(s)
FastEthernet0/0 is up, line protocol is up
  Internet Address 192.168.1.254/24, Area 0
  Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 10
  Transmit Delay is 1 sec, State DR, Priority 1
  Designated Router (ID) 1.1.1.1, Interface address 192.168.1.254
  No backup designated router on this network
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    oob-resync timeout 40
    Hello due in 00:00:00
  Supports Link-local Signaling (LLS)
  Cisco NSF helper support enabled
  IETF NSF helper support enabled
  Index 1/1, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 0, maximum is 0
  Last flood scan time is 0 msec, maximum is 0 msec
  Neighbor Count is 0, Adjacent neighbor count is 0
  Suppress hello for 0 neighbor(s)

Connectivity Test

On PC1

PC1#ping 192.168.2.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.2.1, timeout is 2 seconds:
.!!!!
Success rate is 80 percent (4/5), round-trip min/avg/max = 136/362/1032 ms

On PC2

PC2#ping 192.168.1.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 132/151/184 ms

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