I would like to know what's the best practice of network design. I found 3 design as shown in the attachment.
First one - Use only way firewall with 3 interface (3 subnets)
Second one - Use 2 firewalls. For the aspect of security, I think this is same as the first one. If I can add one more interface on the front firewall, I can simply remove the second firewall.
Third one - Use 2 firewall. But there is nothing in DMZ. The second firewall has 3 interfaces. DMZ is there.
I think first and second design are the same, what do you think?
Do you think third one is more secure than others? or it's too much?
Those designs here use ISA firewall. If I replace all ISA firewalls by Cisco routers, it should make no difference? I have Cisco 2514 and 2501 router, what kind of design I can do?