OSPF Backbone area 0 decision

Dear all,

I created Area 0 in ZoneA, and in this zone i have other area (1,2,3 ...) . some of this sub area is nbma and some is point to point connection.

I have another ZoneB, and it also have connection to other location over point to point link. From ZoneA link to ZoneB through E1 link (point to point) thus should I assign ABR of ZoneB and its internal router in Area 0 too?
Because i don't want to create virtual ink in ZoneB to other sub area.

Your advise please!
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ikhmerAuthor Commented:
+ ZoneA is a big CityA and in this city there is 3 remote network(office)
+ ZoneB is another big CityB, and it also have 3 or 4 remote offices

                            (Area3)                                            (Area6)
                                  |                                                      |  
           (Area1)----(ZoneA Area 0)============(ZoneB area? )--(Area7)---(Area8)

Don JohnstonInstructorCommented:
First off, this "zone" reference is a bit confusing.

The only thing I would do different is to move Area 8 so that it is adjacent to Area 0. Otherwise, you'll have to create a transit link though Area 7.
ikhmerAuthor Commented:
For Area8, i will create virtual link .
and if ZoneB(cityB) is not assigned as area0 then i need to create virtual link for area 7 also.

My question is should I assign ZoneB network as Area 0 too? thus ZoneA and ZoneB will be in the same area 0
and there will be two DR of Area 0 because link between ZoneA to ZoneB is point-to-point. thus i'm afraid their is problem in SPF calculation.
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Well i don't see any problem in SPF calculation if you configure Zone B to be in Area 0; DR is chosen per link and not per area so you can have as many DRs in any area as per ethernet subnet in an area.

So configure Zone B to be in area 0 and virtual link between area 8 and zone B.

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Don JohnstonInstructorCommented:
>My question is should I assign ZoneB network as Area 0 too?

Yes. Otherwise you'll be dealing with two virtual links and one will be crossing two areas.
ikhmerAuthor Commented:
Thank all for your advise, now i can continue my plan by adding CityB into Area0 .
By the way, in the broadcast network their should be only one DR, one BDR and multiple DROther  thus in my case
I will have two DR , one in CityA internal network and other one in CityB internal network of Area 0

Once again, you can have a DR on a broadcast link, the link between city A and city B is point-to-point and so do not need a DR. You don't necessarily have just one DR in an area. DR is dependent on broadcast link and you can have as many DRs as the number of broadcast link in anhy particiular area. So this design is fine as it is.
Don JohnstonInstructorCommented:
Without knowing the physical topology, it's hard to say how many DR's you'll have. But you are correct that every broadcast network will have a DR and BDR. It's also possible for one router to be the DR on multiple networks.
Nayyar HH (CCIE RS)Network ArchitectCommented:

Just something to bear in mind...

Are Zone A and B one big Autonomous System and adminstartive control? If so, the above solution is best way and keeping it simple.

ikhmerAuthor Commented:
thank all
ikhmerAuthor Commented:
Thank you, good explaination
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