One of the most important and useful features in OPNsense is the firewall rules. With them, OPNsense can control network traffic, and block, allow, or forward packets based on the firewall ruleset.

Before we start creating firewall rules, let's learn about some rule concepts used in OPNsense.

The rule processing order

OPNsense uses the pf with the quick parameter set by default, which means that the matched rule will be processed immediately, on a first-match basis. Otherwise, if we leave the Quick option unchecked in the rule, the last-match basis will be used, which means that all the rules will be processed.

OPNsense divides rules by network interfaces, except for the floating rules, which permit creating rules on any interface and are processed before the rules defined in the interfaces ruleset.

The rule processing order is as follows:

Figure 5.7 – The rule processing order

To see the complete list of rules...