OSPF Virtual Link issue

[libra_ali786]

Please look my topology.

Before creating OSPF Virtual Link between R1&R2 , routing table getting inter area route (circle with red color). I understood with no doubt. The table belong to R2 Router.

But, After creating OSPF Virtual Link between R1&R2 , routing table getting intra area route (circle with red color). Why it change Inter area route into Intra route? I think so it should be inter area route instead Intra area. Please clear my doubt.

Note : The table belong to R2 Router.

[Richard Burts]

Let us start by reviewing what you had in the original setup (no virtual link) and how that impacts the routing table. Then let us look at what changes when you configure the virtual link and its impact on the routing table.

In the beginning network 1.0.0.0 (subnet 1.1.1.0/24) belongs in area 0. R2 has no connection to area 0. So R2 receives an intra area route advertisement from R1 in area 1. So in the routing table of R2 network 1.0.0.0 is an inter area (O IA) route. Then you configure the virtual link between R2 and R1. The virtual link gives R2 a virtual connection to area 0. Now through the virtual link R2 receives all of the LSAs of area 0, including the advertisement of 1.0.0.0. So R2 is now receiving an intra area advertisement for 1.0.0.0. So the routing table of R2 now changes 1.0.0.0 from O IA to O intra area route.

HTH

Rick

[libra_ali786]

Thanks Richard Burts for the reply. I am always like your comments because of your way to explain the issues.

What i understand on your comments:

Point-1 : Before creating the VL between R1&R2 , R2 getting the LSA 3 , and it showing the route O IA. Am i right?

Point-2 : After creating the VL between R1&R2 , R2 got the LSA 1 and it showing the O  because of VL. Am i right?

Point -3 : We can say VL change the LSA type?

If i am correct , let me know.

Thanks

[paul driver]

Hello

Duplicate post - here

[Richard Burts · Accepted solution]

You are welcome. I appreciate the kind words about my contributions. 

I agree with your point 1 and point 2. I want to be very careful about point 3. I would say that VL adds a new LSA type which results in a change in the route type in the routing table. To be precise I believe that R2 still receives the type 3 LSA from R1 on the physical interface. But it also now receives the type 1 LSA on VL. What changes is the route in the routing table and not the LSA itself.

HTH

Rick

[libra_ali786]

Thanks Richard Burts for very well explained point-3.

I am strongly agree with your answer. Because If we get intra and inter area route to pointing the same route then router prefered intra route into the routing table.

Thanks

[Richard Burts]

Yes that is correct that if there is both intra area route and inter area route that OSPF will prefer intra area route. Thank you for marking this question as solved. This will help other participants in the community to identify discussions that have helpful information. These communities are excellent places to ask questions and to learn about networking. I hope to see you continue to be active in the community.

HTH

Rick