26. Irregular area virtual link of OSPF configuration experiment
1. Experimental Topology
After OSPF is configured as shown in the topology, R5 in area2 does not have routes to area3, area0, and area1 because there is an area1 between area2 and area0. For this reason, we can establish a virtual link on R3 and R4.
2. Experimental configuration
R1 configuration
Interface Loopback0
Ip address 1.1.1.1 255.255.255.0
Interface Serial0/0
Ip address 12.1.1.1 255.255.255.0
Router ospf 110
Router-id 1.1.1.1
Network 1.1.1.0 0.0.0.255 area 3
Network 12.1.1.0 0.0.0.255 area 3
R2 configuration
Interface Loopback0
Ip address 2.2.2.2 255.255.255.0
Interface Serial0/0
Ip address 12.1.1.2 255.255.255.0
Interface Serial0/1
Ip address 23.1.1.2 255.255.255.0
Router ospf 110
Router-id 2.2.2.2
Network 2.2.2.0 0.0.0.255 area 0
Network 12.1.1.0 0.0.0.255 area 3
Network 23.1.1.0 0.0.0.255 area 0
R3 configuration
Interface Loopback0
Ip address 3.3.3.3 255.255.255.0
Interface Serial0/0
Ip address 34.1.1.3 255.255.255.0
Interface Serial0/1
Ip address 23.1.1.3 255.255.255.0
Router ospf 110
Router-id 3.3.3.3
Network 3.3.3.0 0.0.0.255 area 0
Network 23.1.1.0 0.0.0.255 area 0
Network 34.1.1.0 0.0.0.255 area 1
R4 configuration
Interface Loopback0
Ip address 4.4.4.4 255.255.255.0
Interface Serial0/0
Ip address 34.1.1.4 255.255.255.0
Interface Serial0/1
Ip address 45.1.1.4 255.255.255.0
Router ospf 110
Router-id 4.4.4.4
Log-adjacency-changes
Network 4.4.4.0 0.0.0.255 area 1
Network 34.1.1.0 0.0.0.255 area 1
Network 45.1.1.0 0.0.0.255 area 2
R5 configuration
Interface Loopback0
Ip address 5.5.5.5 255.255.255.0
Interface Serial0/1
Ip address 45.1.1.5 255.255.255.0
Router ospf 110
Router-id 5.5.5.5
Log-adjacency-changes
Network 5.5.5.0 0.0.0.255 area 2
Network 45.1.1.0 0.0.0.255 area 2
3. Configure OSPF virtual links
At this point, neither R1 nor R5 has routes to each other. We will make the following changes on R3 and R4
R3 configuration
Router ospf 110
Area 1 virtual-link 4.4.4.4
R4 configuration
Router ospf 110
Area 1 virtual-link 3.3.3.3
