In our situation pfsync has a syncif of fxp1, our internal network
gateway interface.

In trying to shutdown pfsync from broadcasting state changes to a non
existant recipient machine we tried the following:

ifconfig pfsync0 down

No effect, but the virtual interface pfsync is down. It was a while before
we realized that since the sync interface is fxp1, and we are explicitly
allowing pfsync traffic on this interface, that state will continue to be
broadcast over fxp1.

We changed pf.conf to block pfsync traffic on fxp1 and it no longer
broadcasts.

Now. I am curious, what is the best way to disable pfsync from
broadcasting on the sync interface without changing the firewall ruleset?

I am thinking: ifconfig destroy pfsync0

Would this uncouple the binding to the sync interface?

Thanks in advance,
Rich