We have, of course, the seemingly ubiquitous firewall. This device, which is software sitting usually at a boundary layer between a trusted and untrusted enclave, typically falls into one of four generally described generations of function. Generation one would be a static packet filter, usually built on a router, the rules would block small numbers of attributes that would be used to define hostile or allowed traffic.

A generation two would be a proxy type, which typically sits across a boundary layer, breaking the logical connection and again, acting as a packet filter, based on a great deal of granular rules. Generation three brought the stateful inspection type into existence, which used even more sophisticated filtration techniques and then, we have the generation X. A not very strictly defined, but one that brings in even more advanced stateful inspection by incorporating the elements of artificial intelligence and machine learning, to advance its functionality even further.

Now, there are various architectures which exist and often act to complicate where these are placed, but are often employed in multiple layers to reflect the defense in depth strategy. So the proxies themselves act as middlemen between internal trusted networks and the outside untrusted ones. So a packet, when it arrives at a proxy firewall, the firewall terminates the connection from the source and acts as a proxy. That is, it stands in your place. For the destination, inspects the packet to ascertain that it's safe before forwarding the packet on to its destination.

Significantly, there is a high degree of filtration logic that a proxy can have, and we have to bear in mind that it also breaks the logical connection to ensure that filtration is performed. Now when the destination system responds, the packet is sent back to the proxy firewall, which will repackage the packet with its own source address and abstract the address of the internal destination of the host system, thus obscuring its genuine position.

Proxy firewalls will also make decision, as do packet filtering firewalls. The proxy firewalls don't allow connection directly between trusted and untrusted sources. Application firewalls are programmed to mediate traffic primarily to web-based applications. Now the configuration options permit security over external threats and bad acting applications and this is a unique feature to application firewalls. They often will use machine learning and artificial intelligence to improve their performance through the various learning patterns.