The NTP time server is a much misunderstood piece of equipment. They are quite simple devices in the sense that they are used for the purposes of time synchronisation, receiving an external source of the time which is then distributed throughout a computer network using NTP (Network Time Protocol).
However, with a myriad of ‘free’ time servers available on the internet many network administrators take the decision that NTP time servers are not necessary pieces of equipment and that their network can do without it. However, there are a huge number of pitfalls in relying on the internet as a time reference; Microsoft and the USA physics laboratory NIST (National Institute of Standards and Time) highly recommend external NTP time servers rather than internet providers.
Here is what Microsoft says:
“We highly recommend that you configure the authoritative Time Server to gather the time from a hardware source. When you configure the authoritative Time Server to sync with an Internet time source, there is no authentication.”
Authentication is a security measure implemented by NTP to ensure that the time signal that is sent comes from where it claims to come from. In other words authentication is the first line of defence in protecting against malicious users. There are other security issues too with using the internet as a time source as any communication with an internet time source is going to require the TCP/IP port to be left open in the firewall this could also be manipulated by malicious users.
NIST too recognise the importance of NTP time server systems for prevention and detection of security threats in their Guide to Computer Security Log Management they suggest:
“Organizations should use time synchronization technologies such as Network Time Protocol (NTP) servers whenever possible to keep log sources’ clocks consistent with each other.”