How do I open a filtered port in pf? I have opened a number of ports, and am familiar enough with pfctl, but even though I have opened various ports, then show up as "filtered" - which means of course that they are not open.

How can I open them, or is it a function of having a suitable app using them?
For example

pass in proto tcp from any to any port 53


In a scan this shows up as


  53 dns Filtered


How can I open this port?
Usually port scanners use UDP and TCP to scan port. Since most implementations of DNS servers use UDP you probably also have to open 53/udp:

pass in proto udp from any to any port 53