selecting these sources. Note that, while NTP detects and rejects loops involving neighboring servers, it does not detect loops involving intervening servers.
It is strongly advised, and in practice for most primary servers today, to employ the authentication or
When planning your network, keep in mind a few generic don'ts, in particular:
•Don't synchronize a local time server to another peer at the same stratum, unless the latter is receiving time from lower stratum sources the former doesn't talk to directly. This minimizes the occurrence of common points of failure, but does not eliminate them in cases where the usual chain of associations to the primary sources of synchronization are disrupted due to failures.
•Don't configure peer associations with higher stratum servers. Let the higher strata configure lower stratum servers, but not the reverse. This greatly simplifies configuration file maintenance, since there is usually much greater configuration churn in the high stratum clients such as personal workstations.
•Don't synchronize more than one time server in a particular administrative domain to the same time server outside that domain. Such a practice invites common points of failure, as well as raises the possibility of massive abuse, should the configuration file be automatically distributed do a large number of clients.
The following diagrams depict typical NTP configurations from large to small networks. Use these as a guide when creating your own.
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