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Networking Fundamentals · Foundational

Network Time Protocol (NTP)

A protocol that synchronizes clocks across network devices and hosts, using UDP port 123.

Definition

Accurate time is required for log correlation, certificate validation, Kerberos authentication (which by default tolerates only 5 minutes of skew) and troubleshooting. NTP uses a hierarchy of strata and can authenticate servers.

Example

ntp server 10.1.1.5 on a Cisco router synchronizes its clock.

Exam tip

NTP = UDP 123; time skew breaks Kerberos and makes logs useless.

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