OSPF - Part 6

OSPF Virtual - Link 

 By default backbone area is require to communication between two different areas. Every time is not possible to every single area to connect with backbone area. So, virtual link provide the connectivity with backbone area through a virtual link.

Virtual link is only assign on loopback interface and where virtual link created that area is called
 Transit area.

Understand the scenario:

      

 Look ..!! In this scenario Area 1 and Area 2 is directly connected with Area 0 (backbone area).
But Area 3 isn't connected directly connected with area 0.

  Here We can create virtual link between Area 3 and Area 0 through area 2 , So Area 2 is considered as a Transit area.

  Configuration of virtual - link 

   1. Provide All IP address as per figure.
   2. Configure OSPF routing on all router but remember this think: on router 9's loopback address
        4.4.4.4 add in area 0 and router 10's loopback address 5.5.5.5 add in area 2.
     
          On Router 9
           Router(config)# router ospf 1
           Router(config-router)# network 4.4.4.0 0.0.0.255 area 0
      
          On Router 10
            Router(config)# router ospf 1
            Router(config-router)# network 5.5.5.0 0.0.0.255 area 2
         
  3. Now create virtual - link:

            On Router 9
              Router(config)# router ospf 1
              Router(config-router)#  area 2 virtual-link 5.5.5.5
      
            On Router 10
              Router(config)# router ospf 1
              Router(config-router)# area 2 virtual-link 4.4.4.4

    Verify the OSPF Virtual - link

            Router# show ip ospf virtual - link



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