Description of problem:

NTP is not an uncommon protocol.

Add UDP port 123 for NTP servers as a service thats available (not active) by default

i.e.

<?xml version="1.0" encoding="utf-8"?>
<service>
  <short>NTP Server</short>
  <description>Allow access to an NTP server.  This requires ntp, OpenNTPd or some other ntp daemon to be running</description>
  <port protocol="udp" port="123"/>
</service>