What does NTP stand for?
NTP stands for Network Time Protocol. Synchronizes device clocks with a reference time source over UDP port 123, using stratum levels (stratum 0 is the atomic or GPS clock itself). Skewed clocks break Kerberos authentication, certificate validation and log correlation.
NTP keeps the clocks of computers and network devices in step, using UDP port 123. Time sources are arranged in levels called strata: a stratum 1 server is attached directly to a reference clock such as a GPS receiver, a stratum 2 server synchronizes with a stratum 1 server, and so on. Accurate time is a security requirement. Logs from different systems can only be put in order if their clocks agree, certificates are judged against the current time, and Kerberos refuses sign-ins when clocks differ too much.
NTP in practice: an example
After a firewall replacement, users in one office cannot sign in to the domain. The domain controller there has drifted eight minutes, because the new firewall blocks UDP port 123 and the server can no longer reach its time source. Once the port is allowed, the clock corrects itself and sign-ins work.
What NTP is confused with
NTP vs PTP: what is the difference?
NTP is accurate to milliseconds over ordinary networks, which is enough for logs and sign-ins. Precision Time Protocol reaches far finer accuracy on a local network with supporting hardware, for uses such as industrial control and telecoms.
NTP vs SNTP: what is the difference?
Simple NTP uses the same packet format with a reduced algorithm. It suits small devices that only need roughly correct time.
Which exams cover NTP?
NTP is on the official CompTIA acronym list for two of the four exams covered here.
- Network+ N10-009: 1.0 (Networking Concepts); 3.0 (Network Operations).
- A+ 220-1201 and 220-1202: 220-1201 2.0 (Networking).
Each number is a CompTIA exam objective and the name in brackets is its domain. The exam puts the term in a scenario; it does not ask you to recite the expansion.
Check yourself: two practice questions
Written by CertSprint for this page. They are not taken from any exam.
1. An analyst cannot put firewall, server and switch logs into a single timeline because the timestamps disagree. What should have been configured?
- NTP on all devices
- A larger log disk
- Port mirroring
- A second DNS server
Show the answer
A. NTP on all devices. Correlating events needs a common time source. NTP keeps every device's clock aligned.
2. Which port must a firewall allow so that internal servers can synchronize time with an external NTP server?
- TCP 25
- UDP 123
- TCP 443
- UDP 69
Show the answer
B. UDP 123. NTP uses UDP port 123. The other ports belong to SMTP, HTTPS and TFTP.
Sources: RFC 5905: Network Time Protocol Version 4: Protocol and Algorithms Specification; NIST glossary: Network Time Protocol. The acronym and its expansion come from CompTIA's official acronym lists, linked from each exam glossary above. The explanation, example and questions are CertSprint's own, checked against these sources on 11 November 2026.