Last October I was approached by Poul-Henning Kamp, a self-styled “Unix guru at large”, and one of the FreeBSD developers. One of his interests is precision timekeeping and he runs a stratum 1 timeserver which is located at DIX, the neutral Danish IX (Internet Exchange Point). Because it provides a valuable service (extremely accurate timing) to Danish ISPs, the charges for his hosting at DIX are waived.
Unfortunately, his NTP server has been coming under constant attack by a stream of Network Time Protocol (NTP) time request packets coming from random IP addresses all over the world. These were disrupting the gentle flow of traffic from the 2000 or so genuine systems that were “chiming” against his master system, and also consuming a very great deal of bandwidth. He was very interested in finding out the source of this denial of service attack — and making it stop!