[FROG] OSPF: scaling routers in area or areas per se

[Muenz, Michael]

Dear all,

I'm currently designing a new network, it has 2 DC's with each having a 
VPN cluster.
Each VPN cluster has a Firewall Cluster behind and it's set up in a 
circle, so VPN in DC1 has a DCI to VPN in DC2 and a dedicated link to FW 
in DC1.
Same as in DC2 and FW in DC2 has a DCI to FW in DC1. In this circle I'm 
running area 0.0.0.0 and wherever I add a new interface it's known to 
the network.

Now comes the fun part. We have 100 branches and we use OpenVPN to 
connect to one of the VPN concentrators with the second as backup.
The challenge is, that it shouldn't matter where the branch currently is 
connected to, BUT, it's only allowed to be connected to one DC to 
prevent async routing.
Technically this is also easy, but I'm not sure which one scales better:

- Have only one area 0.0.0.0 also on the branches, so over 100 routers 
in one area
- Have for each branch one area, so over 100 areas having only one router
- Running external via BGP and having 100 neighbors with 100 private AS

Anyone here experienced regarding scaling this size?

Thx!

Michael