Where can I find a list of external time synchronization sources?

A. Within Microsoft .NET and Windows 2000 domains, time synchronization is vital to security. As a result, all domain controllers (DCs) automatically perform time synchronization. However, the forest root DC must synchronize with an external time source. A list of external US time sources is available here.

Microsoft maintains a list of external time sources at its Web site.

Microsoft's Web site also provides information about local time servers for other global locations. To set an authoritative time server, type the following command at the command prompt:

 net time /setsntp:ntp0.uk.uu.net 

where ntp0.uk.uu.net is an example of an SNTP time server. Time synchronization uses UDP port 123, so if you use a firewall, this port must be open.