View All Resources

Network Time Protocol (NTP)

NTP is a component of PennNet's Network Names & Numbers.

PennNet NTP Service
Information Systems & Computing operates the Network Time Protocol (NTP) centrally.   
NTP is a mechanism for synchronizing computer clocks across the network. NTP servers provide network-encoded timing signals to clients interested in setting and maintaining their clocks. What time is it now? How fast is time passing?
NTP at Penn is distributed across three servers in multiple, distinct data centers across the Penn campus. Each server has its own, local, high-performance source of reference time derived from the Global Positioning System (GPS).
Using NTP on PennNet
Virtually all platforms are capable of using NTP, and of receiving NTP information from multiple sources simultaneously. Configure your system with the NTP servers shown on the right. Below are some hints for the most common platforms.
  • Apple macOS - In the Date & Time section of the System Preferences, choose the Date & Time tab, check Set date and time automatically, and enter the three server hostnames separated by commas, like this:,,
  • Microsoft Windows - From a command prompt (Start → type 'cmd' → right click the shortcut and run as administrator), issue the following commands to set the server list and force the computer to resynchronize.
  1. w32tm /config /syncfromflags:manual /manualpeerlist:""
  2. w32tm /config /update
  • Linux/BSD/*nix - Refer to the documentation for your platform (e.g. Ubuntu, Red Hat, FreeBSD, or Solaris). In most cases, you will be able to add the following lines to ntp.conf, and restart the ntpd service.
server iburst
server iburst
server iburst

PennNet NTP

NTP Architecture

Each of the three NTP servers is equipped with an embedded reference clock, which is set and disciplined by a radio receiver. The units receive L-band radio signals from the Global Positioning System (GPS) satellites.

NTP Server Specifications

Frequently Asked Questions

If your systems are configured to receive NTP from any of the following names or IP addresses, you should update your configuration as soon as possible to use active, supported time servers.

The retired NTP servers were:


Yes and no. The central DHCP servers will return NTP server IP addresses to clients that request them (DHCP option 42). The NTP servers do not perform broadcast or multicast protocol operations.

The Network Time Foundation maintains a site with copious reference material and links to additional information.

Visit the Time and Frequency Division of the National Institute of Standards and Technology (NIST) to learn more about the Internet Time Service and WWVB Radio Station.

Though we tend to think of its positioning and navigation applications, the Global Positioning System (GPS) also provides high-performance timing signals, which represent another key component of the PennNet NTP Service.