Perimeter Router, Internal Router and Firewall

There are basically few types of perimeter router standards whereby each of them suits differently depending on the size of the corporate network, each standard also provides different level of protection against network attacks. The very basic of perimeter router i'm going to talk about is the "Standalone perimeter router" which is suitable for small business network due to the minimal cost but provides only 1 layer of security.


The standalone perimeter router basically means having a router which is placed between the outside network (Global) and internal network (Local). The router does basic filtering of unwanted traffics and provides minimal protection for the internal network.


The diagram below shows the example of the Standalone Perimeter Router Topology.

Standalone Perimeter Router Topology

The next standard will be the Perimeter router with a standalone firewall. The perimeter router will again be placed between the outside network (Global) and internal network (Local).  On top of that, there will be a firewall placed just before the perimeter router within the internal network. The firewall provides greater protection and flexibility such as having packet filtering, stateful filtering, application layer filtering and NAT which is suitable for medium to large business network.

The diagram below shows the example of the Perimeter Router and Firewall Topology. 

Perimeter Router and Firewall Topology

The last standard will have at least 3 layer of protection, the perimeter router, a standalone firewall and an internal router. The internal router is to provide mitigation function of the network in case the trusted network inside had been compromise to prevent spreading of the attacks to the DMZ side. On top of that, the router also provides better routing options thus improving the performance of the network.

The diagram below shows the example of the Perimeter Router, Firewall and internal router Topology. 

Perimeter Router, Firewall and internal router Topology.

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