But when used in relation to IP services, "ports" are not physical. The term "port" can refer to a physical hole in a device where you plug something in (such as, "serial port" or "ethernet port"). In order to help systems understand what to do with the data that flows into them, the geek gods conceived ports. Remote terminal access (For example, Telnet, Secure Shell, RDP, or VNC).Translating a host name into an Internet address (using the Domain Name Service, or DNS).File transfer (using the File Transfer Protocol, or FTP).E-mail (using the Simple Mail Transfer Protocol, or SMTP).World Wide Web access (using the Hyper-Text Transfer Protocol, or HTTP).What are services? The five most commonly-used Internet services are: Since the whole Internet comes to your system over one big wire, how does your network distinguish streaming video from a Web page, and an email from a sound file? The answer is complex, but part of it is, the geek gods (read: inventors of Internet Protocol, or IP) came up with services and ports. This knowledge provides you a starting point for figuring out what Internet traffic to permit through the firewall, and what to deny. However, the primary mechanism firewalls used to rely on for allowing or denying network traffic is ports and services. So, a good first step in managing your firewall is to get a quick and dirty understanding of how ports work, and what a given port is used for. Reading that, you might moan, "Argh! This box was supposed to solve my security problems! Now it's waiting for me to tell it what to do! What do I do?" Nowadays, next generation firewalls (NGFW) allow you to make policies using many attributes, including ports and services, users and groups, and even by defining granular access policies to specific network applications (using something referred to as application control). You're the one who categorizes types of network traffic as "good" or "bad." ![]() ![]() The firewall just follows a set of rules, often referred to as policy, that you define. Like the strainer a chef pours his soup stock through, a firewall stops all the bones (bad stuff), but lets all the broth (good stuff) through - at least, in theory.īut how does a firewall know what's bad, and what's good? How can it tell whether a data packet contains an attack, or information you've been eagerly awaiting? It can't. However, in computer networking the term "firewall" means something porous. It evokes something impenetrable, like a sheet of steel or a brick wall. When used in construction or engineering, the term "firewall" means what it seems to mean: a wall capable of withstanding fire. By Scott Pinzon, updates by Corey Nachreiner
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