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NTP Overview Configuring Network Time Protocol (NTP)
page 3-6 OmniSwitch 6600 Family Switch Management Guide March 2005
Examples of these are shown in the simple network diagram below:
Servers 1a and 1b receive time information from, or synchronize with, a UTC time source such as a radio
clock. (In most cases, these servers would not be connected to the same UTC source, though it is shown
this way for simplicity.) Servers 1a and 1b become stratum 1 NTP servers and are peered with each other,
allowing them to check UTC time information against each other. These machines support machines 2a
and 2b as clients, and these clients are synchronized to the higher stratum servers 1a and 1b.
Clients 2a and 2b are also peered with each other for time checks, and become stratum 2 NTP servers for
more clients (3a and 3b, which are also peered). In this hierarchy, the stratum 1 servers synchronize to the
most accurate time source available, then check the time information with peers at the same stratum. The
stratum 2 machines synchronize to the stratum 1 servers, but do not send time information to the stratum 1
machines. Machines 2a and 2b in turn provide time information to the stratum 3 machines. It is important
to consider the issue of robustness when selecting sources for time synchronization.
It is suggested that at least three sources should be available, and at least one should be “close” to you in
terms of network topology. It is also suggested that each NTP client is peered with at least three other
same stratum clients, so that time information crosschecking will be performed.
Note. Alcatel’s current implementation of NTP only allows the OmniSwitch to act as a passive client, not
as a server. A passive client only receives NTP information and adjusts its time accordingly. In the above
example, an OmniSwitch could be either Server 3a or 3b. An OmniSwitch as Server 3a or 3b would also
not be able to peer with other servers on the same stratum.
UTC Time Source
NTP
Servers
NTP
Server/Clients
NTP
Clients
Stratum 1
Stratum 3
Stratum 2
1a 1b
2a 2b
3a 3b