Network Security Basics

Firewalls, VPNs, and network segmentation — the perimeter and internal controls that limit blast radius.

What it is

Network security controls where traffic is allowed to flow, limiting both external attack surface and how far an attacker can move after an initial compromise.

Key points

Firewalls: filter traffic by rules (IP, port, protocol); modern next-gen firewalls also inspect application-layer content.
VPNs: encrypt traffic over an untrusted network, extending a private network's trust boundary — traditionally used for remote access to internal resources.
Network segmentation: dividing a network into isolated zones (e.g. public-facing, application, database tiers) so a breach in one segment doesn't automatically expose the rest.
Zero trust is the modern evolution of this idea — instead of trusting anything inside the perimeter, every request is authenticated and authorized regardless of network location.