Firewalls – Application Proxy Gateways

An application-proxy gateway is a feature of advanced firewalls that combines lower layer access control with upper layer functionality. These firewalls contain a proxy agent that acts as an intermediary between two hosts that wish to communicate with each other, and never allows a direct connection between the two hosts.

Each successful connection attempt actually results in the creation of two separate connections—one between the client and the proxy server, and [..]

Firewalls | Packet Filtering

The most basic feature of a firewall is the packet filter. Firewalls that are only packet filters—also known as stateless inspection firewalls—are essentially routing devices that provide access control functionality for host addresses and communication sessions. Unlike more advanced filters, packet filters are not concerned about the content of packets.

Their access control functionality is governed by a set of directives referred to as a ruleset. Packet filtering capabilities are built [..]

IPv6

IPv6 is a new version of IP that is increasingly being deployed. Although IPv6’s internal format and address length differ from those of IPv4, many other features remain the same—and some of these are relevant to firewalls.

For the features that are the same between IPv4 and IPv6, firewalls should work the same. For example, blocking all inbound and outbound traffic that has not been expressly permitted by the firewall policy [..]