Why not use an Internet time server?
Internet-based time servers operated by universities and government organizations are available for public use. However, NTP requires an open port (UDP port 123) in the firewall for the NTP packets to get through. Open ports in the firewall are a security risk for you, as a network operator, and can effect the reliability and accuracy of public time servers as they are easily exploited in “Denial of Service” attacks even if inadvertent. In May 2003, an internet time server operated by the University of Wisconsin, Madison was the recipient of a continuous large-scale flood of traffic resulting in greatly reduced availability of the server for many months. It was later determined that the source of the “attack” was based on a programming bug in the firmware of inexpensive routers for home and small business use. Accuracy is another concern of internet time servers. The latest survey of the NTP time server network from MIT uncovered two problems: the number of bad time servers on the inte
