This network and the research underpinning it, originally funded based on the utility for military purposes in one country, has far surpassed its original aims, and through international research and uptake, spawned a phenomenon that is shaping (and will shape) generations to come. Networking is now a core activity not just to governments and research organizations, but also to companies small and large, and even home users. Further developments such as the inception of wireless technology have served to make this technology even more accessible (and relevant) to people at home, on the go, and in the imminent future, virtually anywhere on the surface of the planet!

Many of these networking protocols were originally designed in an environment in which the word 'hacker' had not yet come to have the (negative) meaning that it nowadays has, and implemented upon a network in which there was a culture of mutual trust and respect. IPv4, the foundation of all communications via the Internet (and the majority of private networks) and SMTP (the protocol used to send electronic mail and relay it from to server to server) are two prime examples of this. Neither protocol, in its initial incarnation, was designed with features designed to maintain the three qualities that nowadays are synonymous with effective communication, Confidentiality, Integrity, and Availability (called the CIA triad). The CIA triad is often defined as the aim of information security— http://en.wikipedia.org/wiki/CIA_triad. Spam and Denial of Service attacks are just two examples of (malicious) exploitations of some of the weaknesses in these two protocols.

As networking technologies grew and were adopted by governments and large organizations that relied upon them, the need for these three qualities increased, and network firewalls became a necessity. In short, the need for network security sprung into existence. The Internet has come a long way too from its humble beginnings. As the barrier for entry has decreased, and knowledge of the technologies underpinning it has become more accessible, it has become a decreasingly friendly place.

With growing reliance on the Internet for communications, firewalls have, at time of writing, become almost universally deployed as a primary line of defense against unauthorized network activity, automated attacks, and inside abuse. They are deployed everywhere, and the term 'firewall' is used in this context to refer to anything from a software stack built into commonly used operating systems (such as the Windows firewall built into Service Pack 2 of Microsoft's Windows Operating System (http://www.microsoft.com/windowsxp/using/security/internet/sp2_wfintro.mspx)) protecting only the computer it is running on, to devices costing significant sums of money deployed in banks, datacenters, and government facilities (such as Cisco's PIX line of firewall products (http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/)). Such high-end devices may govern and restrict network traffic between hundreds of thousands of individual computers.

Given this increase in the use of the term 'firewall', and with so many qualifiers added to the word to distinguish between different types of firewall (such as the terms stateful, proxy, application, packet filter, hardware, software, circuit-level, and many more), it becomes very difficult to know what someone means when they tell you that their network "has a firewall". Our exploration of IPCop, therefore, must begin with an exploration of what a firewall actually is, and armed with this knowledge, we can then relate IPCop to this knowledge and understand what function it is that IPCop can fulfill for us.

In order to improve our network security, we need to first identify the problems we need to solve, and determine whether this firewall is the solution to them. Implementing a firewall for the sake of satisfying the buzzword requirement is a common mistake in security design.

The term firewall refers, generally, to a collection of technologies and devices all designed to do one thing—stop unauthorized network activity. A firewall acts as a choke point between more than one network (or network segment), and uses a (hopefully) strictly defined set of rules in order to allow, or disallow, certain types of traffic to traverse to the other side of the firewall. Most importantly, it is a security boundary between two or more networks.

In the diagram above, a web server connected to the Internet is protected by a firewall, which sits in between it and the Internet, filtering all incoming and outgoing traffic. In this scenario, illegitimate traffic from the attacker is blocked by the firewall. This could be for any number of reasons, such as the service the attacker has attempted to connect is blocked by the firewall from the Internet, because the attacker's network address is blacklisted, or because the type of traffic the attacker is sending is recognized by the firewall as being part of a Denial of Service attack.

In this scenario, the network that the web server sits on (which in a scenario such as this would probably contain multiple web servers) is segmented from the Internet by the firewall, effectively implementing a security policy dictating what can go from one network (or collection of networks) to the other. If our firewall disallowed the attacker from connecting to a file-sharing port on the web server, for instance, while the 'user' was free to access the web server on port 80, the other servers behind the firewall might be allowed access to the file sharing ports in order to synchronize content or make backups.

Layered protocols are generally explained using the Open System Interconnection (OSI) layers. Knowledge of this is extremely useful to anyone working in networking or with firewalls in particular, as so many of the concepts pertaining to it require knowledge of the way in which this layering works.

The OSI layers divide traffic and data into seven layers each of which in theory falls into a protocol. Although excellent in theory, networking and IT applications do not always strictly adhere to the OSI Layers, and it is worth considering them to be guidelines rather than a strict framework. That said, they are extremely useful for visualizing connectivity, and in general the vision of layers, each utilizing hardware and software designed by different vendors, each interoperating with the layers above and below is not unrealistic.