Network security encompasses the tools, techniques, and practices to protect a network from threats. These tools include both hardware and software and can protect against a variety of threats.
Although the topic is too broad for much detail here, we will cover a few topics that you are likely to encounter.
Firewalls are one of the most common network security techniques. Firewalls act as a barrier between one network and another. As commonly used, they monitor network traffic and allow or block traffic based on a defined set of rules.
Firewalls come in two types: software and hardware. Most operating systems provide software firewalls now. Software firewalls are typically configured to deny incoming connections unless a rule is set up to allow it explicitly.
It is also possible to configure software firewalls to deny outgoing traffic by default. In this case, programs aren't allowed to establish new connections unless a specific rule is added to the firewall configuration first...