OSPF virtual-link

Hi Friends,

 

I have the below network design.

 

AREA0 ----AREA1----AREA2----AREA3

 

Inorder to make the connectivity from AREA2 to AREA 0 I can create a virtual-link with AREA1 as a transit area.

 

How can I connect AREA3 to AREA0 or the design will not work ?

 

Thanks,

Arun Mohan

 

 

Comments

  • JoeMJoeM ✭✭✭

    Interesting scenario.

    Chain them together.       

    AREA 0 <-- area 1 virtual-link   <-->   area 2 virtual-link <-->  area 3 virtual-link <--> etc etc etc

     

    For verification, ping a prefix in Area 0  from the last router in Area 3.

  • Hi,
    You can do virtual links between all areas, like this :
    - 1 vl btw a0 and a1
    - 1 vl btw a1 and a2
    - 1 vl btw a2 and a3

    Check on router in area3 for area0 prefixes.

    Sent from my iPhone

    On 17 Jul 2014, at 10:54, arun <[email protected]> wrote:

    Hi Friends,

     

    I have the below network design.

     

    AREA0 ----AREA1----AREA2----AREA3

     

    Inorder to make the connectivity from AREA2 to AREA 0 I can create a virtual-link with AREA1 as a transit area.

     

    How can I connect AREA3 to AREA0 or the design will not work ?

     

    Thanks,

    Arun Mohan

     

     




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  • Hi,

    Actually for this design you only need two virtual-links configured : one FROM router between area 0 and area 1 TO router between area 1 and area 2 and  one FROM the router between area 1 and area 2 TO the router between area 2 and area 3.

     

    Remember that OSPF virtual link will not come up if the non-area 0 that you are building the virtual-link upon has any type of stub flag set.

    In this case, for example, if area 2 is defined as stub, totally-stub, nssa or totally nssa, the virtual link will not be formed. The solution for this design would be creating an OSPF area 0 adjacency over a GRE tunnel over the "stub" area.

     

     

  • JoeMJoeM ✭✭✭

    Actually for this design you only need two virtual-links configured : one FROM router between area 0 and area 1 TO router between area 1 and area 2 and  one FROM the router between area 1 and area 2 TO the router between area 2 and area 3.

    Great point.   That does simplify the setup a little.    I actually built a mini-lab in GNS3 and extended it out to a chain of five Areas.

  • Hi All,

    I quickly created a GSN3 topology and it is working fine for me with two virtual link

    Please find the below link to see the network diagram and configurations

     

    https://docs.google.com/file/d/0B71gZ5_tSGknenlwM1hleW9QR0U/edit

     

    Thanks,

    Arun Mohan

  • Hi Arun,

    It sure does work :) with one VL between R2 and R3 and another between R3 and R4. 

    Glad you got it done !

  • Hi Ciprian,

     

    Any other solution is to solve this issue other than Virtual-Link.

    Can we use a GRE tunnel with AREA 0.

    But it seems we need to create the GRE tunnel between R3 and R2 and R4 and R3.ie two GRE Tunnel with out doing any static route.

     

    Thanks,

    Arun Mohan

  • Hi Arun,

    That's correct, gre tunnel placed in area 0 could solve the case also. You would create the tunnel having the source and the destination of the directly connected interface and placing the interface into ospf area 0.

    In this case the GRE tunnel config created between R2 and R3 would look something like this :

    R2 :

    int tu 23

    ip add 10.0.23.2 255.255.255.0

    tunnel source 155.1.23.2

    tunnel destination 155.1.23.3

    ip ospf 1 area 0

     

    R3 :

    int tu 23

    ip add 10.0.23.3 255.255.255.0

    tunnel source 155.1.23.3

    tunnel destination 155.1.23.2

    ip ospf 1 area 0

     

    In this case R3 would not need the virtual link to R2, as it's connected to area 0 through the GRE tunnel.

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