Hello Ridhwan
Generally speaking, that sounds like a good plan. When you have a topology with many branch offices connected to an HQ over WAN links, it’s a good design policy to have each branch configured in a different OSPF area, and have the backbone area reside at the HQ. This kind of approach has several advantages including:
- scalability
- reduced routing overhead since ABRs can perform summarization and branch offices can be configured as stub networks
- localization of changes - changes in the network topology within one area do not affect the entire network
It can get somewhat complicated, so you have to make sure your configs are correct and consistent across all branches.
However, in your particular case based on the last topology you shared, you have two WAN links on each of your branch routerσ, and each link is configured on a different non-backbone OSPF area.
This arrangement with two links can be troublesome because OSPF requires that all communication between non-backone areas take place via the backbone area. In other words, all ABRs must have at least one interface in Area 0. By having branch office routers connected to Areas 10 and 20 and not to Area 0, you are violating that rule.
So if you do make the branch office routers ABRs, at least one of their interfaces must be on Area 0. Does that make sense?
I hope this has been helpful!
Laz