Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

OSPF Virtual Link question

I attached a JPG of a lab setup, my question is about a virtual link would be needed if either the link would fail from Router 1 (Area 0) to Router 3 (Area 120) or Router 2 (Area 110).

Cisco Employee

OSPF Virtual Link question


Your topology is not clear - where are the individual areas' boundaries?

Best regards,


Super Bronze

Re: OSPF Virtual Link question


The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.


To clarify what Peter is asking, you need to clarify what area each interface is in.  Each link needs both sides within the same area (if you want the two routers to become OSPF adjacent).  So for example, the R1<>R2 interfaces might both be in area 0 or both be in area 2.  Or the R2<>R3 interface might both in in area 2 or both in area 3.

In general to "share" routing topology between areas (not routers), you need an area zero connection.  For example, if R2's interface to R1 was in area 2 and R2's interface to R3 was in area 3, the R2 router would "know" the topology of both area 110 and 120, but it would "share" the 110 topology with R1 (if it had some area 0 interface) but it would not "share" the 120 topology with R1 or with any other area 110 routers connected to it.

If the R1<>R2 link failed, in the topology I just described, R2 would know of R1 because it has an interface in area 120, but R1 would not "know" of R2.  Also, any other area 110 routers would not know of area 0.