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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).

2 REPLIES
Cisco Employee

OSPF Virtual Link question

Richard,

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

Best regards,

Peter

Super Bronze

Re: OSPF Virtual Link question

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Posting

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.

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