Quick test: does your firewall survive a basic port scan?

Many firewalls get configured correctly at installation and are never touched again. New services get added, ports get opened for a one-off project and forgotten. Here's how to quickly see what's actually exposed.

Test from the outside, not the inside

A test run from your internal network won't show what an outsider sees. Use an external tool, for example ShieldsUP! or Nmap run from a server outside your network, to scan your public IP address.

What to look for

• Ports that are "open" but not tied to a service you actually use
• Admin interfaces (routers, NAS, cameras) reachable directly from the internet
• Old services that should have been shut down long ago

If you find something

Close the port if you don't know why it's open. If you're unsure whether something is safe to close, it's better to ask than guess, a wrongly closed port is noticed immediately, but an open port that shouldn't be can sit undiscovered for years.