Why are we required area 0 in OSPF || interview question ||

[Umesh Prajapati11238]

Dear All,

One day I have been asked a question by the interviewer - why are we required area 0 in OSPF.

As per the my Knowledge I have answered to him -

OSPF area 0 (why area 0 must be presented)

OSPF acts as a distance vector protocol between areas. And because of this OSPF uses a backbone area, area 0, to exchange routes between other areas. This is the reason area 0 exists to prevent the routing loops.

I want to confirmed you all, Is it correct answer that I have answered to interviewer.

Or any other answer would be.

Please reply .

Thank you all. 

[paul driver]

Hello
Your answer is not to bad, however importantly is Ospf is a link state protocol
Additionally you could have said its designed to have a faster to converge then distance vector protocols, it supports equal cost multipath (ecmp) and its not propriety meaning it’s an open protocol. It uses areas to segregate the advertisement and flooding traffic thus cuts down on cpu memory resources of the rtrs, the backbone area (area 0) is used to interconnect those areas 

[Gaurav Kansal]

Dear Umesh,

You could configure a router with two OSPF areas and make both not area zero. The router will allow you to configure this and does not generate any error message. The OSPF will run in both areas but the areas do not share any routes with each other.

The reason for this is that OSPF uses LSA type 1 and LSA type 2 to advertise routes within the area and uses LSA type 3 to advertise between areas. In OSPF (at least in Cisco implementation) the router will not generate any type 3 unless it is connected to area 0.
Area zero, by design, is special in that other areas will accept and provide routes to it. (NB: area types and special OSPF statements define and control route exchanges between an non-zero area and area zero.)
The reason for OSPF areas and area zero is to provide scalability. This two level hiearchy limits the footprint of Dijkstra's algorithm topology (per area) and allows control of route distribution between areas.

GoodLuck..

[gnijs]

?

i would have just said: "area 0 is just needed when you want to connect multiple areas". In fact, you don't need an area 0 at all, you can perfectly put 4 routers into an area 1.1.1.1 for example. And it will work. However, it won't scale. You can't do filtering, you cannot connect another area, you don't have hierarchy, etc etc. In order for two and multiple area's to connect and in order to have a hierarchy and filtering, you need an area 0.0.0.0

[MHM Cisco World]

area 0 is mandatory for any network have multi area 
area 0 is prefer to config as area in any network have single area 

[Joseph W. Doherty]

"area 0 is mandatory for any network have multi area"

Technically, it's not mandatory, but multi-areas do work so much better when there is an area zero.  ; )

[Joseph W. Doherty]

I hate interview questions when the interviewer doesn't actually know the subject (unknown if this is the case, here), and so cannot discuss the subject with you (to ascertain whether you actually know and/or understand the subject).

For example, if I were asked "why are we required area 0 in OSPF.", I might respond, who says we are or under what conditions do you have in mind.  (For examples of where area zero is not required, a couple of posters have described using multiple OSPF areas without requiring area zero.)

Problem is, interviewer might be just looking for a "text book" answer, much like yours (which if fairly good for such), and if so, if your "text book" answer matches theirs, you're golden.  Not so good, otherwise.  Again, if interviewer is only looking for the specific verbiage they want, not much you can do (except ask them, after you "failed" the question, what exactly was the answer they wanted - what you learn might be useful on the next such non-SME interviewer you might interview with).