pfSense

Under certain circumstances the contents of an alias can still be affected by rules after having been removed from the alias in question.

• Create an alias for example called Blackhole with a single host w.x.y.z
• Set rule to block all traffic to/from alias Blackhole
• Reload filters as appropriate
• Verify all traffic is indeed blocked to/from the contents of the alias Blackhole, being the single host w.x.y.z
• Go to the alias, and remove the single host w.x.y.z, leaving the alias Blackhole empty
• Reload filters as appropriate
• Observe that all traffic is still blocked to/from the host, w.x.y.z, even though it is no longer in the alias Blackhole
• Adding another host to the now "empty" alias solves the problem