Home of the Network Time Protocol - 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), pool.ntp.org, and related projects.
LinuxDevCenter.com: Synchronizing Networks with NTP - Accurate timekeeping is vital to accurate records, and accurate logs are the mainstay of good system administration. Glenn Graham explains NTP (the Network Time Protocol) and how to put it to work on your network.
Network Time Synchronization Project - 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.
The NTP FAQ and HOWTO - Understanding and using the Network Time Protocol (A first try on a non-technical Mini-HOWTO and FAQ on NTP)
NTP Servers Web - 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.
NTP Statistics Gathering and Reporting with MRTG - David Taylor's short description of how he uses MRTG (and SNMP) to gather and report statistics for NTP for his servers, including Perl scripts, shell scripts, and mrtg.conf examples
NTP Support Web - 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 others within the community. Anyone who is interested in helping to develop or improve documentation for NTP is encouraged to join and contribute.
O'Reilly Cisco Cookbook - 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.
O'Reilly Hardening Cisco Routers - Sample chapter from the book, showing the cisco-specific methods of configuring your routers to support using NTP time synchronization.
pool.ntp.org: The Internet Time Network - Information on a collection of public NTP servers provided by users and ISP's placed in a DNS round-robin under pool.ntp.org.
RFC2030 - Simple Network Time Protocol Version 4 - 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.
Vendor: endruntechnologies.com: Introduction to NTP - Four page document that gives a very simple high-level overview of how NTP works and some of the issues to be considered when looking to set up NTP time servers. This company is a vendor of NTP time servers and related hardware. [PDF]
Vendor: Sun Blueprints Online: Using NTP on the Sun Fire 15K/12K Server - This article addresses the time skew issues for the Sun Fire 12K/F15K server and explains how the system controllers and domains can be configured as NTP clients to external servers. A sample configuration is also provided. This article is targeted to the intermediate level of expertise. [PDF]