NTP official reference implementation (for Unix and Unix-like OSes, with ports to Microsoft Windows NT, VMS, real-time OSes like VxWorks and QNX). Also jumping-off point to the official NTP documentation and FAQ, community documentation tools (twiki),...

Information on a collection of public NTP servers provided by users and ISP's placed in a DNS round-robin under pool.ntp.org.

NTP Project page for Dr. Mills, primary NTP researcher for over twenty years. He and his students are working on NTP version 4 to improve robustness and security.

Community maintained list of public Stratum 1 and Stratum 2 NTP time servers, including policies and requirements for use, contact information. Maintained via the NTP TWiki, by the admins of the respective sites themselves.

The current NTP standard. Available here in HTML, PDF, and Postscript formats.

Not the official NTP documentation or the official NTP FAQ. Intended to be the collection point for cookbook configurations, tips, hints, tricks, and other comments from directly from various members of the NTP community that might be beneficial to ot...

Report by Dave Plonka on the massive problems caused on the University of Wisconsin network and time servers, due to misconfiguration of NetGear equipment

Understanding and using the Network Time Protocol (A first try on a non-technical Mini-HOWTO and FAQ on NTP)

The current standard for SNTP, a version of the protocol for implementations which do not need all of the features of NTP. Available here in HTML, PDF, and Postscript formats.

This book gathers hundreds of example router configurations all in one place. In chapter 14, the authors provide information on configuring, running, and debugging NTP on your Cisco router. This link via O'Reilly's Safari network for online publications.