Thank you for your reply.
Here is the thing:
1.) You have 30 Private Neworks which are segrated into 3 Network Domains each one of them having 10 of those Private Networks.
2.) Each Domain has a router which interconnect all the 10 networks belonging to that Domain.
3.) Now you want to securely connect these three domains so there is a Firewall to which the uplink of each domain router is connected to.
So under this scenario we have one Firewall connecting 3 routers and each router connecting 10 networks together.
I was thinking to get rid of the "Routers" and just connect all 30 Networks Directly to the Firewall but I do have the following concerns:
1) Can a Firewall work properly as a router between private network domains?
2) Nowadays what's the maximum number of ports (Network Interfaces) a firewall can support?. The number of networks on each domain will growth so at some point I may run out of spare ports on the Firewall.
3) While using the firewall in combination with the routers I think loading will get more balanced since the firewall only needs to deal with trafic across Domains while the Routers will handle all the trafic internal to the domains + the inbound/outbout trafic associated with that domain only.
So Firewall resource loading is another issue I would need to address if I remove the routers don't you think?.
If you have any comments or feedback on the above 3 concerns I will much appreciate it. (or perhaps a new design concept)