ACLs and Firewall Routers
Another type of firewall implementation uses two or more routers to provide the security. The border router, A, is ultimately responsible for securing the LAN(s).
The firewall router, F, is responsible for protecting both the shared servers and the internal networks from attack from outside. In an optimal solution, this would be a specialty device like Cisco’s PIX box, which combines hardware and software to secure the connection. Whether a specialty device or a router with the firewall feature set, ACLs will be a part of the solution.