Firewall - What it is, why you need one, and safe default settings

Firewall

What it is

A firewall is a gatekeeper for your network - it filters traffic so only approved connections get through. Firewalls can be hardware (built into routers or dedicated appliances) or software (on your computer or server). For a deeper look at setup options and use cases, see our 
firewall explainer

Why it matters

Most attacks start with a connection from the outside - or a risky app calling out. A well-tuned firewall blocks malware, scans, and suspicious traffic while letting normal work continue.

How it works

  • Rules & policies - allow known-good ports, block the rest

  • Stateful inspection - track conversations so replies are allowed, fakes are not

  • Next-gen features - app awareness, IPS, malware filtering, DNS controls

Good defaults

  • On endpoints - enable the built-in OS firewall and block inbound by default

  • On routers - close unused ports, disable remote admin from the internet

  • For services - put apps behind a reverse proxy or WAF, and limit who can reach admin panels

Quick setup wins

  1. Start with deny by default - allow only what you need.

  2. Limit RDP/SSH/VPN to specific IPs - require MFA.

  3. Turn on logging and alerts - review new blocks weekly.

  4. Pair with DNS filtering and auto-patching for layered protection.

  5. Test from the outside - use a port scan to confirm nothing extra is open.

    Glossary (A–Z)

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