It is important to know how NTP works before you set it up. Several of the comments seem to be misguided. NTP is a peer-to-peer protocol, there are no such thin

It is important to know how NTP works before you set it up. Several of the comments seem to be misguided. NTP is a peer-to-peer protocol, there are no such thing as an "NTP server" or an "NTP client". NTP measures clock drift over a server group. It discovers enough about your topology to assign a statistical factor to each peer, so that a rogue or broken server can not bring down the whole group. Known good time (which is what the stratum value is, a measure of distance to known good time) is then sprinkled in from several sources to drift the time in the direction of true time. Exactly as you should have a number of secondary DNS servers in different AS, you should use several different time sources from different organizations. If you are bigger than a closet shop, you might as well put your own GPS receiver in there too when sparkfun sells them for $40, and enable authentication on it.