Overview of NTP

Definition

Network Time Protocol (NTP) is an application layer protocol belonging to the Transmission Control Protocol/Internet Protocol (TCP/IP) suite. NTP synchronizes time between time servers and clients. NTP implementation is based on Internet Protocol (IP) and User Datagram Protocol (UDP). NTP transmission occurs through UDP port 123.

Purpose

As network topologies become increasingly complex, clock synchronization becomes more important for all devices within a network. Manual configuration of system clocks by network administrators is both labor-intensive and error-prone, potentially affecting clock precision. NTP operates as a network protocol which synchronizes the clocks of devices within a network.

NTP is applied when all devices on a network require consistency between their clocks, such as in the following situations:

When in network management, routers require timestamps on analysis logs and debugging messages collected from different routers.
When an accounting system requires that all device clocks be consistent.
When multiple systems must reference the same clock when operating together to process complicated events.
When performing incremental backup, a backup server and clients require synchronization between clocks.
When certain applications require access to user login or file modification times.

Switch can function as both the NTP server and NTP client.

Version Evolution

NTP evolved from a simple time protocol using the ICMP Timestamp message. NTP has grown in complexity, now maintaining time synchronization with improved security and reliability. Table 1 lists the NTP versions and their updates.

**Table 1** NTP version evolution
Version	Date	Standard	Description
NTPv1	June 1988	RFC 1059	NTPv1 encompasses complete NTP rules and algorithms, but does not support authentication and control messages.
NTPv2	September 1989	RFC 1119	In addition to encompassing complete NTP rules and algorithms, NTPv2 supports authentication and control messages.
NTPv3	March 1992	RFC 1305	NTPv3 utilizes correctness rules while improving clock selection and filter algorithms. NPTv3 has been widely adopted, and only operates on an IPv4 network.
NTPv4	June 2010	RFC 5905	While similar to NTPv3, NTPv4 operates on both IPv4 and IPv6 networks. NTPv4 is backward compatible with NTPv3, and provides a complete encryption and authentication system, which is lacking in NTPv3.