OpenNTPD configuration guide

OpenNTPD supports IPv6 at least since version 3.6.p1. In its ntpd.conf configuration you must define which local IP addresses it listens on:

# any IPv4/IPv6 addresses
listen *
# IPv4 loopback address
# listen 127.0.0.1
# IPv6 loopback address
# listen ::1

You can specify multiple listen <local IPv4/IPv6 address> instructions if you wish.