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OSPF Virtual Link

Written by Rene Molenaar on . Posted in OSPF

Scenario:

You are a freelance network engineer specialized in routing and switching. One of your customers (a local butcher) has some trouble setting up their OSPF network. Some of the networks are not reachable and it's up to you to provide them with a solu

Goal:

  • All IP addresses have been preconfigured for you as specified in the topology picture.
  • Each router has a loopback0 interface.
  • Configure OSPF on all routers.
  • Ensure you restore connectivity for the discontigious backbone area 0.
  • Ensure area 2 has connectivity to the backbone area.

IOS:

c3640-jk9s-mz.124-16.bin

Topology:

OSPF Virtual Link Network Topology

Video Solution:

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Comments (5)

  • avatar
    mistborn_soother
    2012-03-26 03:51:03

    I am not sure why router FISH would need a virtual link setup on it as it already has connectivity to the backbone because BEEF is the ABR and has an interface in area 0

  • avatar
    daliusgikaras
    2012-03-29 08:05:38

    Router beef is internal area 1 router, not ABR. Virtual link between Pork an Chicken do not make router beef an ABR. So we need at least 2 virtual links i this lab:
    1. Pork - Chicken
    2. Fish - Pork or Fish - Chicken

  • avatar
    ReneMolenaar
    2012-04-01 09:52:39

    This is correct. Router Beef is just an internal router for area 1. Fix those two virtual links and you have fixed this issue.

    Keep in mind you can also use GRE tunnels instead of the virtual links to fix these problems. That's not something you would normally do but it's something the CCIE students should remember :)

  • avatar
    Dardoufa
    2012-05-10 08:27:00

    Hello

    Out of curiosity I wanted to try out the solution with the GRE tunnels.
    I use tunnels only to connect router Fish with router Chicken. For Chicken and Pork I use the virtual link.

    So, what I configured is this. 10.1.1.0/24 is used for the tunnel interface.

    On Chicken:
    interface Tunnel1
    ip address 10.1.1.1 255.255.255.0
    tunnel source FastEthernet0/0
    tunnel destination 192.168.24.4

    router ospf 1
    log-adjacency-changes
    area 1 virtual-link 3.3.3.3
    network 1.1.1.0 0.0.0.255 area 0
    network 10.1.1.0 0.0.0.255 area 2
    network 192.168.12.0 0.0.0.255 area 1

    On Fish:
    interface Tunnel1
    ip address 10.1.1.4 255.255.255.0
    tunnel source FastEthernet0/0
    tunnel destination 192.168.12.1

    router ospf 1
    log-adjacency-changes
    network 4.4.4.0 0.0.0.255 area 2
    network 10.1.1.0 0.0.0.255 area 2
    network 192.168.24.0 0.0.0.255 area 1

    Fish#sh ip ospf ne

    Neighbor ID Pri State Dead Time Address Interface
    2.2.2.2 1 FULL/DR 00: 00 :34 192.168.24.2 FastEthernet0/0
    1.1.1.1 0 FULL/ - 00: 00 :35 10.1.1.1 Tunnel1

    And now I can ping:
    Fish#ping 1.1.1.1 source lo0

    Type escape sequence to abort.
    Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
    Packet sent with a source address of 4.4.4.4
    !!!!!
    Success rate is 100 percent (5/5), round-trip min/avg/max = 44/53/68 ms

    Is this the correct way to go about it?

  • avatar
    ReneMolenaar
    2012-05-10 08:58:08

    Yes that looks fine to me! Create a GRE tunnel, configure a subnet on it and run OSPF on it :)