Perimeter defence

You have just seen the network building blocks and as mentioned those elements need protection. There are many ways to protect the network. The first one you will look at is establishing a perimeter defence.

The first stage of creating a perimeter defence is to implement a firewall. Firewalls are network devices that isolate and control the flow of traffic between networks of varying trust levels. Generally, they provide security at the network layer rather than the application level, although there are application firewalls.

Firewalls help protect internal networks from the Internet and enforce access policy. They provide comprehensive auditing of the connections that traverse them and allow granular access control.

The output of a firewall log can be treated as an alarm to inform the security team when someone’s doing something or accessing something they shouldn’t. Many firewalls also double up as the endpoint of encrypted virtual private network tunnels or provide the access control mechanisms for remote access users, like home or mobile workers.

Figure 1: Perimeter defence