Common NTP Client Problems
The most troublesome problems have involved NTP server addresses hardcoded in the firmware of consumer networking devices. As major manufacturers produce hundreds of thousands of devices and since most customers never upgrade the firmware, any problems will persist for as long as the devices are in service.
One particularly common software error is to generate query packets at short (less than five second) intervals until a response is received. When such an implementation finds itself behind a packet filter that refuses to pass the incoming response, this results in a never-ending stream of requests to the NTP server. Such grossly over-eager clients (particularly those polling once per second) commonly make up more than 50% of the traffic of public NTP servers, despite being a minuscule fraction of the total clients. While it is reasonable to send a few initial packets at short intervals, it is essential for the health of any connectionless network that unacknowledged packets be generated at exponentially decreasing rates. This applies to any connectionless protocol, and many portions of connection-based protocols. Examples can be found in the TCP specification for connection establishment, zero-window probing, and keepalive transmissions.
Read more about this topic: NTP Server Misuse And Abuse
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