New OSPF sim for ICND1 on GNS3 | 100-101 Practice Lab

OSPF Lab on GNS3 for ICND1: 

In network diagram you can find the three router R1, R2 and R3. R1 and R2 are already configured with IP addresses and OSPF area 0. You need to perform the following tasks and configurations:

  1. Configure last available IP address of f0/0 of R3 with first usable subnet
  2. Configure first available IP address for S1/0 with second usable subnet from the network
  3. Configure OSPF with area 0 on R3 so that R3 can properly communicate with R1 and R2 

You can practice this LAB on GNS3 by downloading R1 and R2 configuration other necessary detail for GNS3 configuration are as under:

Router IOS= 7200 series (you can download it from here)
GNS3 version= GNS3 1.0 beta2
Router module/slot used: slot1=c7200-IO-2FE, slot2=PA-8T
(Note: for quick configuration you can download these text files and can copy paste these configuration into your GNS3 router)

Configure f0/0 with first useable subnet from

For finding the first useable subnet you can consider the following table:
Subnetting for
Bit# in 4th octet

IP ranges/ increment

From above table you can find following subnets with the increment of 16 for

Subnet1= to               (Subnet ID=
Subnet2= to             (Subnet ID=
Subnet3= to             (Subnet ID=

Since we need to assign last available IP address from subnet1, therefore we have the last IP address=

R3> enable
R3# config t
R3(config)# int f0/0
R3(config-if)# ip address
R3(config-if)# no shut

2. Configure first available IP address to S1/0 with second usable subnet from the network

For above table we have already find that second subnet is to with first IP address=

R3(config)# int S1/0
R3(config-if)# ip address
R3(config-if)# no shut

3. Advertise both interface of R3 in OSPF:

You can advertise these two subnet on R3 using Subnet-IDs by following commads:

R3(config)#Router OSPF 1
R3(config-router)#network area 0
R3(config-router)#network area 0

Results and testing:

After the correct configuration you should have the following output for “show IP route” command:

After the configuration you should have successful ping to

If you have any trouble/issue with R3 configuration you can also download R3 configuration from here and can compare it to your configuration.

Test you ICND1 skills by taking ICND1 Quiz Questions and Answers 

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