Keeping your network synchronized with the correct time is crucial for modern networking. Because of the value of timestamps in communciating globally and across multi-networks, it is imperative that every machine is running a source of UTC (Coordinated Universal Time).
UTC was developed to allow the entire global community to use the same time no matter where they are on the globe as UTC doesn’t use time-zones so it allows accurate communication regardless of location.
However, finding a source of UTC is often where some network administrators fall down when they are attempting to synchronize a network. There are many areas that a source of UTC can be received from but very few that will provide both accurate and secure reference to the time.
The internet is full of purported sources of UTC, however, many of them offer no where near their acclaimed accuracy. Furthermore, resorting to the internet can lead to security vulnerabilities.
Internet time sources are external to the firewall and therefore a hole has to be left open which can be taken advantage of by malicious users. Furthermore, NTP, the protocol used to distribute and receive time sources, cannot instigate its authentication security measure across the internet so it is not possible to ensure the time is coming from where it is supposed to.
External sources of UTC time are far more secure. There are two methods used by most administrators. Long wave radio signals as broadcast by national physics laboratories and the GPS signal which is available everywhere on the globe.
The external sources of UTC ensure your NTP network is receiving not just an accurate source of UTC but also a secure one.