Perimeter Router, Internal Router and Firewall

The perimeter router is typically a standard router providing a serial connection to the outside world and a LAN connection to the internal network. The perimeter router should provide any filtering of outside traffic to implement basic security for the DMZ and preliminary filtering for the inside network. This device could be running the firewall feature set for additional security options.

A firewall can either be software-based or hardware-based and is used to help keep a network secure. Its primary objective is to control the incoming and outgoing traffic of network by analysing the data packets and determining whether it should be allowed through or not, based on a predetermined rule set. A network's firewall builds a brigade between an internal network that is assumed to be secure and trusted, and another network, usually an external (inter)network, such as the Internet, that is not assumed to be secure and trusted.

The internal router takes care of the internal network of the company such as NAT.

Such as network that has all 3 are more common in medium and large business where they would need greater protection and performance and well as greater routing options. The firewall is separated from the router and there is 1 router to take care of the external and internal network. The workload is split between different machines and therefore, they would be able to perform better and they have more computing resource to perform that function.