OSPF Virtual Link Lab

This lab was taken from gns3vault.com. Click here to go to the lab page.

Table of Contents

Goal

All IP addresses have been preconfigured for you.

  1. Configure OSPF on all routers, configure the areas as specified in the topology picture.
  2. Area 2 has no direct connection to Area 0, solve this by using OSPF commands.
  3. Ensure you have full reachability.
  4. Create some extra loopbacks on router Louie and advertise them in area 2:
    • Loopback0: 172.16.0.1 /24
    • Loopback1: 172.16.1.1 /24
    • Loopback2: 172.16.2.1 /24
    • Loopback3: 172.16.3.1 /24
  5. Make sure router Huey only sees 172.16.0.0/22 in it's routing table, you are only allowed to make changes to router Dewey.

Topology

c4ospf3.png

Configuration

1

Huey(config)#router ospf 1
Huey(config-router)#network 192.168.12.1 0.0.0.0 area 1
Huey(config-router)#network 1.1.1.1 0.0.0.0 area 0

Dewey(config)#router ospf 1
Dewey(config-router)#network 192.168.12.2 0.0.0.0 area 1
Dewey(config-router)#network 192.168.23.2 0.0.0.0 area 2

Louie(config)#router ospf 1
Louie(config-router)#network 192.168.23.3 0.0.0.0 area 2

2

The rule states that no LSA's may be exchanged directly between non-backbone areas. In other words, LSA's between area 1 and area 2 can only travel through area 0.

Virtual Link creates a tunnel for area 2 to reach area 0 through area 1.

Dewey(config)#router ospf 1
Dewey(config-router)#area 1 virtual-link 1.1.1.1

Huey(config)#router ospf 1
Huey(config-router)#area 1 virtual-link 192.168.23.2

The virtual-link requires the router ID as an argument. This is another reason to manually configure the router ID. If it somehow changes in the future, the virtual link dies.

3

Louie#ping 1.1.1.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 40/44/48 ms

4

Creating the loopbacks:

Louie(config)#int l0
Louie(config-if)#ip add 172.16.0.1 255.255.255.0
Louie(config)#int l1
Louie(config-if)#ip add 172.16.1.1 255.255.255.0
Louie(config)#int l2
Louie(config-if)#ip add 172.16.2.1 255.255.255.0
Louie(config)#int l3
Louie(config-if)#ip add 172.16.3.1 255.255.255.0

Advertising into OSPF area 2:

Louie(config)#router ospf 1
Louie(config-router)#network 172.16.0.1 0.0.0.0 area 2
Louie(config-router)#network 172.16.1.1 0.0.0.0 area 2
Louie(config-router)#network 172.16.2.1 0.0.0.0 area 2
Louie(config-router)#network 172.16.3.1 0.0.0.0 area 2

Huey can see the networks:

Dewey#sh ip route
[...]
C    192.168.12.0/24 is directly connected, FastEthernet0/0
     1.0.0.0/32 is subnetted, 1 subnets
O       1.1.1.1 [110/2] via 192.168.12.1, 00:04:57, FastEthernet0/0
     172.16.0.0/32 is subnetted, 4 subnets
O       172.16.1.1 [110/2] via 192.168.23.3, 00:00:27, FastEthernet1/0
O       172.16.0.1 [110/2] via 192.168.23.3, 00:00:27, FastEthernet1/0
O       172.16.3.1 [110/2] via 192.168.23.3, 00:00:27, FastEthernet1/0
O       172.16.2.1 [110/2] via 192.168.23.3, 00:00:27, FastEthernet1/0
C    192.168.23.0/24 is directly connected, FastEthernet1/0

5

This summarization is not possible on Louie because it is not an ABR.

Dewey(config)#router ospf 1
Dewey(config-router)#area 2 range 172.16.0.0 255.255.252.0

Dewey acts as ABR between area 1 / area 2 and area 0 and it is the only router that can create the summary route.

Huey#sh ip route
[...]
C    192.168.12.0/24 is directly connected, FastEthernet0/0
     1.0.0.0/24 is subnetted, 1 subnets
C       1.1.1.0 is directly connected, Loopback0
     172.16.0.0/22 is subnetted, 1 subnets
O IA    172.16.0.0 [110/3] via 192.168.12.2, 00:00:04, FastEthernet0/0
O IA 192.168.23.0/24 [110/2] via 192.168.12.2, 00:00:37, FastEthernet0/0
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