Network Time Protocol (NTP)

The Network Time Protocol (NTP) is one of the most accurate and flexible means of sending time over the Internet. It can be used by almost any type of computer. The protocol is designed to compensate for some, but not all, network time delays between the server and the client. NTP is most successful across local area networks and can give accuracy as good as a few milliseconds. On the World Wide Web however, time transfer delays are at the mercy of server traffic and network bottlenecks, and accuracy figures cannot be quoted as easily.

NTP supports security measures for users who want more reassurance concerning the origin of the time stamp, rather than insecure NTP. The NRC offers Authenticated NTP service on the NRC stratum-2 servers free of charge. Please contact us for more information.

To make use of NTP service and have your computer's clock set to NRC time, you will need software that can request time over the Internet.

A version of the NTP client software used to synchronize computer clocks is called Simple Network Time Protocol (SNTP). The software for various computers can be downloaded from many sites on the Internet.

To configure SNTP software to synchronize your clock to NRC time, you must set the NTP server to the following stratum-2 host names (do not use the IP address, as this may change):


For users who have an NTP server on their system and would like to synchronize to NRC time, configure your daemon to include the above NTP server address.

The NRC operates two sets of stratum-2 NTP servers at two different locations operating on different networks. Both servers are controlled in the same way by atomic clocks operated by the NRC and provide official time with the same accuracy. This redundant setup offers a more reliable time service to Canadians in cases of network and maintenance outages.

The NRC offers new NRC TimeLinkTM - Monitored NTP service for users who require service from a stratum-1 server. Please contact us for more details.


Due to security concerns NRC no longer provides TIME (port 37) and DAYTIME (port 13) services that were previously available at For the most accurate time transfer, ensure your clock synchronization software is configured to use the NTP or SNTP protocols.

Technical notes

The NRC's Network Time Protocol complies with version 4 specification as outlined in RFC-5905. The servers also support the Simple Network Time Protocol (SNTP).

For a complete explanation of the Network Time Protocol and the latest information on NTP, visit the NTP source.

There are 3 stratum-1 server hosts at each network site. These are computers using the Linux operating system. An NTP host operating as a primary or stratum-1 time server is directly synchronized to a source of accurate time. At the NRC main lab, the 3 stratum-1 servers are connected to Leitch 5300 Master Clock drivers which are synchronized to 3 separate cesium atomic frequency standards. The secondary site is at radio station CHU. Here the reference clocks are the code generators that create the broadcast code used by the shortwave transmitters. The code generators are synchronized to atomic clocks.

The NRC also operates stratum-2 servers that disseminate NTP time. Our stratum-2 servers are computers with the Linux operating system. They get their time from the 3 stratum-1 servers. For all practical purposes, the average time disseminated by the stratum-2 server is the same as the stratum-1 servers.

The service at and is actually served by multiple servers at different IP addresses in a round-robin configuration for redundancy and load balancing. The DNS server will resolve the lookup to a specific machine. Do not use the IP addresses, as these may change. Both and provide official time for Canada with the same accuracy

A note of warning to users who are trying to synchronize a computer protected by a firewall; make sure your firewall allows incoming NTP packets from our servers to your computer. If not, you will not be able to synchronize your computer to our time service.

Contact us

Telephone: 613-993-5186