Security5 min read
The firewall rules that actually matter
Default deny, a short allow-list, and the three ports people leave open without meaning to. Practical rather than paranoid.
A firewall is a list of what is allowed, and everything else is refused. The mistake is not usually a missing rule; it is a rule added during troubleshooting at three in the morning and never removed.
The shape of a good rule set
- Deny by default. Everything after this is an exception you can justify.
- The game or web port, open to everybody. That is the service.
- Administrative access - SSH, RCON, database - restricted to addresses you control.
- Nothing else. If you cannot say what a rule is for, remove it and see who complains.
The three that get left open
A database port opened to test a connection from home. An RCON port opened for a tool that was uninstalled a year ago. A debug or admin panel bound to all interfaces because that was the default. All three are ordinary, and all three are how servers are found.