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NTP Overview Configuring Network Time Protocol (NTP)
page 3-4 OmniSwitch 6600 Family Switch Management Guide March 2005
NTP Overview
The Network Time Protocol (NTP) is used to synchronize the time of a computer client or server to
another server or reference time source, such as a radio or satellite receiver. It provides client time accura-
cies within a millisecond on LANs, and up to a few tens of milliseconds on WANs relative to a primary
server synchronized to Universal Coordinated Time (UTC) (via a Global Positioning Service receiver, for
example). Typical NTP configurations utilize multiple redundant servers and diverse network paths in
order to achieve high accuracy and reliability. Some configurations include cryptographic authentication to
prevent accidental or malicious protocol attacks.
It is important for networks to maintain accurate time synchronization between network nodes. The stan-
dard timescale used by most nations of the world is based on a combination of UTC (representing the
Earth’s rotation about its axis), and the Gregorian Calendar (representing the Earth’s rotation about the
Sun). The UTC timescale is disciplined with respect to International Atomic Time (TAI) by inserting leap
seconds at intervals of about 18 months. UTC time is disseminated by various means, including radio and
satellite navigation systems, telephone modems, and portable clocks.
Special purpose receivers are available for many time-dissemination services, including the Global Posi-
tion System (GPS) and other services operated by various national governments. For reasons of cost and
convenience, it is not possible to equip every computer with one of these receivers. However, it is possi-
ble to equip some computers with these clocks, which then act as primary time servers to synchronize a
much larger number of secondary servers and clients connected by a common network. In order to do this,
a distributed network clock synchronization protocol is required which can read a server clock, transmit
the reading to one or more clients, and adjust each client clock as required. Protocols that do this include
NTP.
Note. The Alcatel OmniSwitch 6000, 7000, and 8000 series switches can only be NTP clients in an NTP
network. They cannot act as NTP servers.