HP-UX Internet Services Administrator's Guide (February 2007)

NOTE: Broadcasting is not recommended especially when used with local clock
impersonators. Broadcasting is an old concept that is no longer used.
Figure 4-3 illustrates the relationship between time servers in a synchronized subnet.
Figure 4-3 Example of Relationships Between Time Servers
Planning a Multiple-Server NTP Configuration
You must consider the following guidelines when planning your configuration:
• Every NTP hierarchy must have atleast one stratum-1 server. You can configure
the administrative domain to contain outside sources of synchronization, which
ultimately link to stratum-1 server, or you can implement your own hierarchy of
NTP time servers with one or more stratum-1 servers.
• Configure atleast three time servers in the administrative domain because it is
important to provide multiple, redundant sources of time synchronization. NTP
is designed to select an optimal source of synchronization from several sources.
Each time server must be a peer with each of the other time servers.
• For each time server, select one or three outside sources of synchronization. This
assures a relative degree of reliability in obtaining time, when you select sources
that do not share common paths. The sources must operate at a stratum level that
is one less than the local time servers.
• Each outside source of synchronization must be in different administrative domains,
and you must access the sources from different gateways and access paths. You
must avoid loops and common points of failure. Do not synchronize multiple time
servers in an administrative domain to the same outside source.
Advanced NTP Topics 61