Time Synchronization in an NT Network

Network time synchronization is an important part of network design and implementation. You need a time-synchronized network for healthy operation of network operating systems and applications; synchronization is critical for businesses that depend on a computer network. For example, many network directory services systems exchange information and synchronize changes in the directory services database according to time stamps. Groupware applications require accurate time for scheduling and collaboration. Without a time-synchronized network, time-sensitive systems and applications will not work correctly. In a Windows NT network, all NT servers and client workstations need to synchronize with a single, accurate, and standard time source.

Although Microsoft doesn't supply a built-in time service in NT, the Microsoft Windows NT Resource Kit CD-ROMs for NT 3.51 and 4.0 provide a TimeServ utility. TimeServ is an NT service that can synchronize the system time with a time source either on the network or from outside. Microsoft also provides a network command, NET TIME, that synchronizes a computer on a Microsoft network with network time. This article introduces the two Microsoft time synchronization utilities, outlines how to design a time-synchronized NT network, and guides you in configuring and implementing time synchronization.

Windows NT Time Service
TimeServ works with NT Server and NT Workstation 3.5, 3.51, and 4.0. Because TimeServ is an NT service, it runs in the background even when no one is logged on the system. TimeServ keeps an NT computer synchronized with standard time from a remote site or on the network. Components of time synchronization are standard time sources, master time servers, primary time servers, and secondary time servers.

A remote time service provider is a standard time source. Generally, it is a standard Greenwich Mean Time service provider, such as the National Institute of Standards and Technology (NIST) in Boulder, Colorado, or the US Naval Observatory (USNO) in Washington, D.C. You can obtain the standard time using a modem or the Internet.

An NT server or workstation is called a master time server if it obtains standard time from a remote standard time source or from a network time server that supports Network Time Protocol (NTP) on IP. The master time server then provides this standard time to the rest of the network. At least one master time server must be on a time-synchronized network. For redundancy, two or more master time servers can be on the same network. However, Microsoft recommends that all master time servers use the same standard time source.

An NT server or workstation is a primary time server if it obtains network time from a specific NT time server on the network. This server is generally a master time server or an NT time server that provides good time on the network. A server provides good time if its time drifts less than 0.5 second from system time. The time service records time drift in the Application log of the Events Viewer when the time service sets the system time to network time. If the time drifts more than 0.5 second, the server may need to obtain time more frequently. Any number of primary time servers can be on the network.

An NT server or workstation is a secondary time server if it obtains network time from a specific NT domain. This domain can be the same domain in which the secondary time server resides, or a different domain, if no time server is in the same domain. Typically, you configure at least one primary time server to be the time source that answers time requests from the secondary time server. In some cases, you can use a master time server or even a secondary time server as a time source, too, although a secondary time server is usually a client of a time source.

Multitiered Time Synchronization System
You can envision NT network time synchronization as a multitiered time synchronization system. A master time server at the top of the system obtains standard time from a remote standard time source and then provides this time to the entire network. Primary time servers in the middle of the system obtain network time from a master time server and then give this time to secondary time servers and client workstations. Secondary time servers and client workstations reside at the bottom of the system and get network time from a primary time server. Secondary time servers and client workstations are network time clients. Figure 1 shows this multitiered time synchronization system.

Microsoft Network Time Command
Another way to synchronize time on a network is with Microsoft's NET TIME network command. NET TIME is a DOS command for computers running NT, Windows 95, Windows for Workgroups, or DOS/Windows with Microsoft network client software. When you execute the NET TIME command, the workstation sets its system to network time by searching for a time source in the domain. If a time source is not present, the workstation will obtain time from a domain controller. For an NT computer, you can issue the command

NET TIME /DOMAIN:<domain_name> /SET /Y

to set the time to network time. For a non-NT computer, you can enter the command

NET TIME /WORKGROUP:<domain_name> /SET /Y

A computer can also synchronize its time with a specific computer if you enter the command

NET TIME \\<computer_name> /SET /Y

You must assign Change the system time to the user on the workstation so that NET TIME can work.

NET TIME works well for workstations when you add it to an NT domain logon script. When a workstation logs on to a domain, the workstation system time is set to the network time. TimeServ is a better utility for NT servers, because it runs in the background.