NTP is an abbreviation of Network Time Protocol, which is a standard internet protocol that was established over twenty years ago. NTP time servers are network appliances that are designed to disseminate accurate time to client computers and network infrastructure for synchronization purposes.
This article provides a brief overview on a number of topics associated with the installation and configuration of a NTP time server appliance:
- NTP Server Hardware Installation.
- NTP Appliance Configuration.
- Hardware Reference Clock options, GPS, MSF, DCF-77 and WWVB.
- NTP Security and Authentication.
- Client Configuration.
- Simple Network Time Protocol (SNTP)
NTP time servers are generally network appliances provided in desktop or rack-mountable enclosure. They are intended to be housed in a typical computer room with other servers. The appliances are designed to obtain very accurate time from a hardware reference clock, such as GPS or one of the many national radio time broadcasts available. They use this accurate time to synchronize an internal clock and in turn provide accurate time to other networked devices. Network Time Protocol is designed to operate on a typical TCP/IP network using the UDP datagram protocol.
NTP Time Server Hardware Installation
Stratum 1 NTP server systems rely on an external timing reference to obtain accurate time. Various external timing references are available. Options may vary with according to the regional location of the installation.
The Global Positioning System – GPS
GPS has a number of advantages over national radio hardware clock references:
- It is highly accurate, to within less than a microsecond of UTC.
- GPS is a satellite based system that is available world-wide.
- It provides a continuously available signal, 365 days of the year.
- It is not affected by local topology. All that is required is that an antenna is provided with a good view of the sky.
GPS also has a couple of disadvantages, but these are generally far outweighed by the advantages discussed above:
- A roof mounted antenna is generally required to obtain a good GPS lock, increasing installation costs.
- It is considered good practice to install a surge suppressor to any externally mounted antenna. This provides protection against potential lightning strikes and other voltage surges.
- Installers need to be aware of coax cable types for antenna installations, lower-loss cable is required for longer cable runs.
National Radio Time Broadcasts
Radio time broadcasts are available in many countries. These broadcasts have a finite range and are therefore regional, generally limited to national boundaries. Radio signals can often be received indoors and so require less effort and expense to install. However, the signals can be prone to local interference and also metal structures which reflect and block the radio signals. Also, radio time broadcasts are not as accurate as GPS. Typically, synchronization to with a few milliseconds is achievable rather than microseconds with GPS. Additionally, many radio transmissions are also prone to going off-air for days or even weeks at a time for maintenance and repairs. To summarise, a number of factors can affect radio reception:
- Locating an antenna underground or in a basement.
- Placing the antenna inside a metal cage or enclosure, including metal clad buildings.
- Locating the antenna too close to electrically noisy equipment.
A number of national radio time broadcasts are available including:
- MSF-60, transmitted at 60 KHz from Anthorne, UK and is available throughout the British Isles and much of North-Western Europe.
- DCF-77, transmitted at 77.5 KHz from Frankfurt, Germany and is available throughout much of Central and Western Europe.
- WWVB, transmitted at 60 KHz from Colorado, USA and is available throughout much of the United States and Canada.
NTP Server Configuration
NTP time servers are very easy to configure and install. There are a large number of options available to configure a NTP daemon, but for all but a very few applications, the default configuration is more than adequate. It is, however, good practice to assign a static IP address to a NTP server rather than a leased DHCP assigned address. Once configured, the appliance then needs to synchronize with the selected hardware time reference before it can provide time to clients. This process is a calibration process which can take up to 20 minutes to complete.
NTP Security and Authentication
An option that many organisation prefer to have is NTP authentication, which is a means of secure communication between a client and NTP server. NTP implements MD5 authentication which allows timestamps to be securely transmitted between a server and client and prevent any possibility of tampering.
NTP Client Configuration
Most modern operating systems have built-in NTP or SNTP clients which can easily be configured to synchronize to a NTP server. All recent Microsoft Windows operating systems along with UNIX, LINUX and Novell all have clients available. A minimum client install and configuration requires only the IP address of the server to which it is to synchronize.
As well as servers and workstations, many network appliances can also accept time from a NTP server. Appliances such as routers, switches, IP cameras, Digital Video Recorders (DVR’s) can all be synchronized.
Simple Network Time Protocol (SNTP)
Simple Network Time Protocol (SNTP) is a simplified version of NTP that lacks some of the intricacies of the full-blown protocol. It is quite often used by workstations and small computers that do not require the precision offered by the full-blown NTP protocol. However, both the NTP and SNTP protocols are completely interchangeable, any SNTP client can obtain time from a NTP server.
NTP time servers are network appliance designed for the purpose of time synchronization of networked devices. They are extremely easy to install, configure and maintain. GPS is generally accepted as the preferred choice of hardware clock, though national radio broadcasts are also an option. Client configuration often consists of only specifying an IP address of a time server.