OSPF Virtual Link Configuration Case Study_4

OSPF Virtual Link

• This Blog contains the OSPF virtual link concepts with configuration on Cisco Routers.
• To know the basic concepts and configuration of ospf- ping here
• After the rush up of those concepts it may ease to follow though this blog.

WHY Virtual Link ?

• Area 0 is the backbone of the OSPF network. It means that all the areas in the OSPF network must connect to the Area 0 .
• What happens if particular area is  not able to connect to the Area 0 ?
• There is two solutions
• one is that we can take a cable from the router from one area that is not connected to the backbone and connect the cable to the Nearest ABR-- This is funny and most probably it is not going to be possible.
• Second is the most Good and Wonder full technique of OSPF that is VIRTUAL LINK.

[caption id="attachment_215" align="alignnone" width="590"] OSPF Virtual Link[/caption]

• Let us take the above example It has Four Routes
• R1 R2 R3 R4
• R1 is ASBR (Autonomous System Boundary Router) as it is connect to the External System
• There are Four Areas :
  • Area 1 - R1 and R2
  • Area 2 - R3 and R4
  • Area 3 - R2 and R3
  • Area 4 - R4 loopback
  • Area 0 (Backbone) - R2 and R3
• All the areas are connected to the area 0 except the Area 4.
• What to do - create  virtual link
• Creating Virtual Link is not so difficult it is just a single command
• Syntax
  • Area <area-id of transmission area> virtual-link <router-id of the nearest ABR>
• Example : Let us consider the above diagram
  • As area 4 is not connected to the area we can make it possible.
  • As we have Two nearest ABR as per the topology that is R2(Area 3 is as the transmission area) And R3 (Area 2 as the transmission area )
  • We can take anyone of the links here we take R3 (Area 2 as the transmission area )
  • goto the router mode and give

  • Area 2 virtual-link 0.0.0.3

• We will need to give the Command in both the Routers  to make the virtual link Up
• In this case we have to give the command at R3 and R4
• Note : The Router Id will change for the commands at different routers.

Configurations:
Router 1 :

• After configuring the Basic IP address configurations.

RIP :
R1(config)#routerRip
R1(config-router)#version 2
R1(config-router)#no auto-summary
R1(config-router)#network 10.0.0.0
OSPF:
R1(config)#router ospf 1
R1(config-router)#router-id 0.0.0.1
R1(config-router)#network 10.1.1.2 0.0.0.0 area 1
R1(config-router)#network 10.1.1.10.0.0.0 area 1

• Redistributing the RIP into the OSPF

• R1(config)#router ospf 1
  R1(config-router)#redistribute rip subnets

Router 2 :

• After configuring the Basic IP address configurations.
  • R2(config)#router ospf 1
  • R2(config-router)#router-id 0.0.0.2
  • R2(config-router)#network 10.1.2.1 0.0.0.0 area 0
  • R2(config-router)#network 10.1.1.2 0.0.0.0 area 1
  • R2(config-router)#network 10.1.3.1 0.0.0.0 area 3

Router 3 :

• After configuring the Basic IP address configurations.
  • r3(config-router)#router-id 0.0.0.3
  • r3(config-router)#network 10.1.2.2 0.0.0.0 area 0
  • r3(config-router)#network 10.1.4.1 0.0.0.0 area 2
• Creating Virtual link
  • r3(config-router)#area 2 virtual-link 0.0.0.4

Router 4 :

• After configuring the Basic IP address configurations.
  • R4(config)#router ospf 1
  • R4(config-router)#network 10.1.4.2 0.0.0.0 area 2
  • R4(config-router)#network 10.1.3.2 0.0.0.0 area 3
  • R4(config-router)#network 172.16.1.1 0.0.0.0 area 4
  • R4(config-router)#end
• R4(config-router)#area 2 virtual-link 0.0.0.3.