Windows 2000 vs. Windows NT Time Synchronization

Customizing Win2K Time Service
Win2K time synchronization automatically works with minimal manual configuration. However, in certain circumstances, you might want to customize Win2K W32Time (e.g., if you're using a Win2K Server system as an SNTP server to avoid synchronization across sites). To customize W32Time, you manually modify the Registry settings in the HKEY_LOCAL_MACHINE\SYSTEM\ CurrentControlSet\Services\W32Time\Parameters subkey. You need to restart the W32Time service for a change to take effect.

By default, when you start W32Time, the service synchronizes system time every 45 minutes until the time successfully synchronizes (i.e., the local system time matches the time source's time) three times. Thereafter, the service synchronizes every 8 hours. If you want the computer to synchronize time every hour, you can change the Period parameter from the default REG_SZ string value SpecialSkew to REG_DWORD decimal value 24. You can also use a W32Time understandable string value to define synchronization frequency in the Period parameter. For example, you can set DailySpecialSkew to synchronize system time every 45 minutes until successful, then to synchronize once daily; WeeklySpecialSkew to synchronize every 7 days; TridailySpecialSkew to synchronize every 3 days; and BidailySpecialSkew to synchronize every 2 days.

By default, when a Win2K domain controller's W32Time service starts, the domain controller automatically works as an SNTP server regardless of whether the LocalNTP parameter's REG_DWORD value is 0 or 1. However, for a Win2K member server or workstation to function as an SNTP server, you must modify the LocalNTP parameter's default value from 0 to 1.

If you have multiple AD sites and the network bandwidth between the sites is limited and expensive, you can modify the AvoidTimeSyncOnWan parameter to save WAN bandwidth. Changing the parameter's value from 0 to 1 prevents a Win2K computer from synchronizing time with a time source in a different site.

By default, a Win2K domain controller is a time source. You can enable a Win2K member server or workstation to be a time source by adding the TimeSource parameter with the REG_DWORD value of 1 to the HKEY_LOCAL_MACHINE\SYSTEM\ CurrentControlSet\Services\LanmanServer\Parameters subkey.

In your Win2K network, only the authoritative time server uses NTP synchronization. You can configure other Win2K computers in your network to use NTP synchronization. To set up this configuration, manually change the Type parameter of the HKEY_LOCAL_MACHINE\SYSTEM\ CurrentControlSet\Services\W32Time\Parameters subkey from NT5DS to NTP and add the NTP server DNS names or IP addresses as a REG_SZ string value to the NtpServer parameter. Alternatively, you can use Win2K's Net Time command to configure W32Time to use an NTP server, and the command will automatically modify the necessary Registry parameters.

Win2K Net Time
Win2K's Net Time command lets you manually synchronize a computer's time with another Windows computer, a PDC, or a time source in the computer's local domain or another domain. In addition, this command lets you easily define, without touching the system's Registry, which NTP servers a system's W32Time service will use. Win2K Net Time uses remote procedure call (RPC) packets for time synchronization, and the command doesn't require NTP.

You can use Win2K's Net Time command to synchronize time with a time source in the network and perform other synchronization functions. Simply enter one of the following commands at a system's DOS prompt:

1. Net Time /set /y synchronizes time with a time source in the local domain.
2. Net Time /rtsdomain:domain_name /set /y synchronizes time with a time source in a different domain.
3. Net Time /domain:domain_name /set /y synchronizes time with the PDC of the domain you specify.
4. Net Time \\computer_name /setsntp:ntp_server_names_or_IP_ addresses synchronizes time with an NTP server.
5. Net Time \\computer_name /setsntp changes the W32Time synchronization type from NTP to NT5DS.
6. Net Time \\computer_name/querysntp lets you query to discover whether a specific computer is using NTP servers and which NTP servers the computer is using.

You can also use the Net Time command to synchronize time from a specific computer (e.g., Net Time \\win2kdc1.acme.com /set /y).

If you don't use the /set and /y switches in the Net Time command, the command displays only the time it obtains from the time source. If you use the /set switch without the /y switch, the command prompts you to change your system time.

Time Synchronization in a Mixed Win2K and NT Environment
As you upgrade your network, you'll have a mixed Win2K and NT environment, and integrating time synchronization in this environment is important. Fortunately, you can use Win2K and NT's time-synchronization tools to easily implement time synchronization in a mixed environment. Let's look at three mixed-environment scenarios: no Win2K domain controllers, Win2K and NT domain controllers, and no NT domain controllers.

Figure 3, page 110, shows a mixed environment that contains Win2K member servers and workstations but no Win2K domain controllers; the Win2K member servers and workstations belong to NT domains. You can continue to use NT time synchronization for your NT computers. However, Win2K member servers and workstations can't use Win2K's default time-synchronization method (i.e., NT5DS) to synchronize time from an NT domain controller because NT5DS can use only a Win2K domain controller as its time source. To solve this problem, you can use NT's W32Time service to configure an NT system as an SNTP server by setting the NT system's Registry LocalNTP parameter to 1 or specifying yes to the LocalNTP setting in NT's w32time.ini initialization file, as Figure 3 shows. After you use NT's W32Time service to set up at least one NT SNTP server in your network, you can then configure Win2K W32Time on your Win2K systems to use the NT SNTP server as their time source. You can also use the Net Time command in your NT domain logon script to synchronize time with the Win2K workstations. This setup saves you from spending time configuring W32Time on your Win2K workstations.

Figure 4 shows a mixed environment that contains Win2K and NT domain controllers. You first need to configure the Win2K PDC of the root domain of the AD forest to use external NTP servers as standard time providers. This root PDC is the authoritative time server for your Win2K computers. All Win2K computers in this environment can follow the default Win2K time synchronization in the AD domain hierarchy. You can also use this authoritative time server for your NT computers. You can retire your NT master time server and use the Win2K authoritative time server as the master time server for all NT primary time servers. You don't need to change the NT secondary time servers' configuration because those servers can obtain time from a Win2K time source. You can use the Net Time command on NT and Win9x systems to specify that they obtain time from a Win2K computer, PDC, or time source. In this mixed environment, you maintain two time-synchronization hierarchies (i.e., Win2K and NT) that share one authoritative or master time server.

Figure 5 shows a mixed environment in which you've upgraded all NT domain controllers to Win2K but still retain NT member servers and workstations. This environment is the last mixed-environment configuration in the natural Win2K upgrade progression. You don't need primary time servers in this environment because your NT member servers can be secondary time servers that obtain time from a Win2K domain controller. NT workstations can use the Net Time command in their domain logon scripts to synchronize time from a time source in the domain.

Happy Synchronization
Win2K's time-synchronization features free network administrators from having to install and configure the time service on multiple NT servers. Win2K's default working time-synchronization system lets you use the Net Time command and Registry modifications to easily customize the OS's time service. In addition, Win2K's full support for SNTP in W32Time makes Win2K time synchronization Internet-ready and lets you synchronize time in your network equipment (e.g., routers, UNIX hosts, other OS computers that support NTP or SNTP). These features, combined with Win2K's easy integration in a mixed Win2K and NT environment, might even make an NT-to-Win2K upgrade enjoyable.