Introduction to Network Security
Network security is the practice of protecting a computer network and its data from unauthorized access, misuse, or attack. As networks grow in complexity and more sensitive data travels across them, understanding the tools and techniques used to secure them becomes essential.
In this subtopic we cover four main pillars of network security:
- Firewalls , controlling traffic entering and leaving a network
- Common vulnerabilities , understanding how attacks happen
- Countermeasures , defenses and best practices
- Encryption and digital certificates , protecting data in transit and verifying identity
- Wireless security , specific protections for Wi-Fi networks
Network security is not a single tool or technique , it is a layered approach. Each layer compensates for weaknesses in another, a concept sometimes called defence in depth.
Firewalls , Function and Types
A firewall is often described as the first line of defence for a network. It sits between a trusted internal network and an untrusted external network (such as the internet), examining traffic and deciding what to allow or block based on a set of predetermined rules.
Firewall: A hardware or software system that monitors and controls incoming and outgoing network traffic based on predefined security rules, acting as a barrier between trusted and untrusted networks.
Firewalls can operate at different levels of the network stack, giving rise to several distinct types:
| Type | How it works |
|---|---|
| Packet filtering | Examines individual data packets (source/destination IP, port, protocol) and allows or blocks them against a ruleset |
| Stateful inspection | Tracks the state of active connections; only allows packets that belong to a known, legitimate connection |
| Application-level gateway (proxy firewall) | Analyses traffic at the application layer, understanding specific protocols (HTTP, FTP, DNS) and filtering accordingly |
| Circuit-level gateway | Monitors TCP handshaking to verify that sessions are legitimate before allowing data to flow |
Think of packet filtering as a bouncer checking IDs at the door , they only look at surface information. A stateful firewall is more like a security team that also watches what each guest does once inside, and can eject anyone who starts behaving suspiciously.
