OSPF Virtual Link

1. OSPF virtual link
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2. 2

3.  From the topology we can see that R1 belongs to Area 0, R2 to 1,
R3 and R4 to 2.
 OSPF working rules say that every area must be connected to
backbone area (Area 0), in this case there is not a physical
connection between Area 0 and 2, that’s why we’ll configure a
Virtual Link between these two areas.
 Before we set up Virtual Link in this topology we’ll configure OSPF
on routers.
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4. R1
 R1(config)#interface Loopback0
 R1(config-if)# ip address 192.168.0.1 255.255.255.0
 R1(config)#interface FastEthernet0/0
 R1(config-if)# ip address 10.0.0.2 255.255.255.0
 R1(config)#router ospf 1
 R1(config-router)# network 10.0.0.0 0.0.0.255 area 1
 R1(config-router)# network 192.168.0.0 0.0.0.255 area 0
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5. R2
 R2(config)#interface FastEthernet0/0
 R2(config-if)# ip address 10.0.0.1 255.255.255.0
 R2(config)#interface FastEthernet0/1
 R2(config-if)# ip address 10.0.1.1 255.255.255.0
 R2(config)#router ospf 1
 R2(config-router)#network 10.0.0.0 0.0.0.255 area 1
 R2(config-router)#network 10.0.1.0 0.0.0.255 area 1
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6. R3
 R3(config)#interface Loopback0
 R3(config-if)#ip address 192.168.1.1 255.255.255.0
 R3(config)#interface FastEthernet0/0
 R3(config-if)#ip address 10.0.2.1 255.255.255.0
 R3(config)#interface FastEthernet0/1
 R3(config-if)#ip address 10.0.1.2 255.255.255.0
 R3(config)#router ospf 1
 R3(config-router)# network 10.0.1.0 0.0.0.255 area 1
 R3(config-router)# network 10.0.2.0 0.0.0.255 area 2
 R3(config-router)# network 192.168.1.0 0.0.0.255 area 2
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7. R4
 R4(config)#interface Loopback0
 R4(config-if)#ip address 192.168.2.1 255.255.255.0
 R4(config)#interface FastEthernet0/0
 R4(config-if)#ip address 10.0.2.2 255.255.255.0
 R4(config)#router ospf 1
 R4(config-router)#network 10.0.2.0 0.0.0.255 area 2
 R4(config-router)#network 192.168.2.0 0.0.0.255 area 2
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8. Neighbor relationship between R1, R2 and R3
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9. Configure virtual link on R1 and R3
R1
 R1(config)#router ospf 1
 R1(config-router)#area 1 virtual-link 192.168.1.1
R3
 R3(config)#router ospf 1
 R3(config-router)#area 1 virtual-link 192.168.0.1
 Where 192.168.1.1 is Router ID of R3 and 192.168.0.1 is Router ID
of R1.
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10.  Let’s check if there are neighbours on this virtual link and to see if R1 has a
route to R4.
Neighbors on R1
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11. Routing table on R1 11

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