This can be a strange concept to understand because, like IP addresses, ports and firewalls don't really "exist" in the physical world. However, were you to send (whether by accident or by design) network data destined for port 22 of that web server, you'd likely be denied by the firewall (and possibly banned for some time). The web server's firewall is programmed to accept incoming traffic destined for port 80, so it accepts your request (and the web server, in turn, sends you the web page in response). When you want to view a website, your computer sends network data identifying itself as traffic destined for port 80 of the web host. Websites, for instance, are hosted on web servers. One thing that network data contains is a port number, which is one of the primary things a firewall uses when accepting or denying traffic. Firewalls are designed based on network protocols, and it's part of the specification of talking to other computers that a data packet sent over a network must announce specific pieces of information about itself (or be ignored). They're running on your mobile phone, on your router, and your computer. A firewall is a daemon programmed to either accept or deny certain kinds of network traffic.įirewalls are relatively small programs, so they are embedded in most modern devices. There are many daemons running on your computer, including the one listening for mouse or trackpad movements, for instance. A firewall is just a computer service (also called a "daemon"), a subsystem that runs in the background of most electronic devices. As technology goes, firewalls have a fun name, but they're actually a little boring. You don't see them (hopefully), but they're there. Ideally, there are firewalls all around you, even now.
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