For the last few years, I have been using net/openntpd instead of FreeBSD's base ntpd(8), exclusively because of the latter's tendency to bind to all available interfaces and addresses, and its inability to be configured in a way that it binds to specific IP address. Things have changed recently, however, and it appears that from FreeBSD 11.1 onwards we can specify ntpd's listen IP address(es). The following article explains how to bind FreeBSD's base ntpd to single IPv4 address, and IPv4 loopback address.