Firewall best practices

From these fundamental principles we can distil a set of best practices for implementing our firewall. Some of these practices are fairly obvious; some may not be quite so obvious:

  • When you create your firewall rules, the principle of least privilege should apply. In many cases, firewall rules have been too permissive. You should try to avoid creating pass-through rules which have any in the destination field, or at least limit the range of ports to which these rules apply. pfSense blocks all network traffic by default, and you'll want to take advantage of that.
  • You should periodically check your firewall rules and delete rules that are out of date. For example, in our example network, we had a printer on the MARKETING subnet ...

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