How it works
The simplest firewall looks at addresses and ports. A stateful firewall remembers who started a connection: it lets in the reply to your request but blocks an unsolicited connection from outside. Modern firewalls also recognise applications and threats in the traffic.
The most common mistakes
- Ports for cameras and a NAS opened directly to the internet.
- UPnP left on, which lets devices open ports by themselves.
- The default password for the router's admin page.
A better approach
Keep services behind the firewall and use a VPN or a tunnel for access from outside. Split devices into separate networks, see VLANs and network segmentation.