Am I using NTP without knowing it?

Yes! Your Android or iPhone smartphone, your Windows, Mac, or Linux computer, your internet router, your GPS, and even your smart TV all use NTP automatically to stay on time. It is invisible and automatic.

What is the difference between NTP and NTS?

NTP transmits time without any particular protection. NTS (Network Time Security) adds a cryptographic security layer: your device can verify that the received time actually comes from the right server and has not been tampered with in transit.

A pool is a group of time servers that work together. Instead of relying on a single server (which could go down), your device can query multiple servers in the pool. The most well-known is ntppool.org: over 4,000 servers worldwide, including ~370 NTP servers in France.

What is NTP in simple terms?

NTP (Network Time Protocol) is like a speaking clock service for devices connected to the Internet. It allows your phone, computer, and connected devices to ask specialized time servers, synchronized to atomic clocks, for the exact time.

Why does accuracy matter?

Imagine an orchestra where each musician had their own clock, slightly off. The result would be cacophony! In the IT world, it's the same: without time synchronization, systems cannot collaborate effectively. Emails arrive "before" they were sent, backups overwrite newer files, logs become incomprehensible...

Understanding NTP and NTS: The Simple Guide

Q: What is NTP? (in 30 seconds)

NTP stands for Network Time Protocol . Imagine a giant speaking clock on the Internet. Your phone, your computer, your router... all these devices regularly ask it: "What time is it exactly?" This "speaking clock" is actually a network of time servers synchronized to atomic clocks — the most accurate clocks in the world, which only drift by one second every 300 million years! In summary NTP = a system that allows all your devices to set their time automatically via the Internet.

Q: What is NTS? (the secure version)

NTS stands for Network Time Security . It is an evolution of NTP that adds a cryptographic security layer.

By Richard DEMONGEOT | January 21, 2026 | Reading time: 10 min

What is NTP? (in 30 seconds)

NTP stands for Network Time Protocol.

Imagine a giant speaking clock on the Internet. Your phone, your computer, your router... all these devices regularly ask it: "What time is it exactly?"

This "speaking clock" is actually a network of time servers synchronized to atomic clocks — the most accurate clocks in the world, which only drift by one second every 300 million years!

How I use NTP without knowing it

Good news (or bad, depending on your perspective): you don't have to do anything! NTP works automatically on virtually all your connected devices.

📱

Android

Automatically synchronized via Google servers or your carrier

🍎

iPhone / iPad

Uses Apple servers (time.apple.com) automatically

💻

Windows

"Windows Time" service enabled by default (time.windows.com)

🖥️

Mac

Synchronized via Apple servers automatically

🐧

Linux

Uses chrony, systemd-timesyncd, or ntpd depending on the distribution

📺

Smart TV

Automatic time setting via Internet or broadcast signal

📡

Internet Router

Synchronized to your ISP's servers

🚗

GPS / Car

GPS satellites also transmit atomic time

How it works

The simple explanation (1 minute)

Your device asks for the time
Your phone sends a request to an NTP server: "What time is it?"
The server responds
The server responds with the exact time, synchronized to an atomic clock.
Offset calculation
Your device calculates the message's travel time and adjusts its own clock.
Regular repetition
This process repeats automatically (every few minutes to every few hours).

Want to see the 4 NTP messages in action? The animated 5-minute explainer on ntp-tester.eu visualises the request/response flow. And to diagnose a machine that does not synchronise correctly, check-ntp.net runs a live scan showing offset, latency and sync status in real time.

A bit more detail (for the curious)

The NTP protocol is organized into hierarchical levels called "Stratum":

            Stratum 0 — Atomic clocks, GPS, radio signals
            
The ultimate source of time (cesium, GPS, etc.)
        
            Stratum 1 — Servers directly connected to atomic clocks
            
Accuracy: a few microseconds
        
            Stratum 2 — Servers synchronized to Stratum 1
            
What most businesses use
        
            Stratum 3+ — Your devices (PCs, phones, servers...)
            
Synchronized to Stratum 2

👉 Go deeper: read our dedicated guide NTP Stratum Levels Explained: From Stratum 0 to 16 — accuracy per level, Stratum 1 vs Stratum 2 comparison, and how to check a server's stratum.

What is NTS? (the secure version)

NTS stands for Network Time Security. It is an evolution of NTP that adds a cryptographic security layer.

Classic NTP

Like a postcard

Time is sent "in the clear"
No sender verification
Someone could modify the message

NTP with NTS

Like a sealed registered letter

The exchange is authenticated (TLS 1.3)
The server's identity is verified
Impossible to tamper with the message

Learn more about NTS and how to enable it →

NTP Pools: Strength in Numbers

Main pools and public servers

Provider	Address	Specifics
Global NTP Pool	pool.ntp.org	Community-run, 4000+ servers
France NTP Pool	fr.pool.ntp.org	~370 French servers
Google	time.google.com	Leap smearing (smooth leap second handling)
Cloudflare	time.cloudflare.com	Supports NTS
Apple	time.apple.com	Used by iOS/macOS
RDEM Systems	ntp-pool.rdem-systems.com	16 servers, NTS enabled, France

The documents that define NTP (RFCs)

NTP is defined by the IETF, in RFCs. Not all of them apply to every server: RFC 5905 describes the protocol, the others extend it, secure it or say how to operate it. The statuses and dates below come from the RFC Editor's official index, checked on 2026-09-21.

RFC	Subject	Status	Date	Relations
RFC 5905	The protocol itself: exchanges, timestamps, stratum, offset and delay computation, source selection. Network Time Protocol Version 4: Protocol and Algorithms Specification	Proposed Standard	June 2010	obsoletes RFC 1305 and 4330; updated by 7822, 8573, 9109, 9748, 9769
RFC 7822	Extension fields: what lets NTS, among others, travel inside an NTP packet. NTPv4 Extension Fields	Proposed Standard	March 2016	updates 5905
RFC 8573	Symmetric-key authentication: MD5 deprecated, AES-CMAC recommended. This is not NTS. Message Authentication Code for NTP	Proposed Standard	June 2019	updates 5905
RFC 8633	Operational best practice: choosing and counting sources, configuration, security. Network Time Protocol Best Current Practices (BCP 223)	Best Current Practice	July 2019	—
RFC 8915	NTS: key exchange over TLS (port 4460), then authenticated NTP packets. Network Time Security for NTP	Proposed Standard	October 2020	—
RFC 9109	Client source ports are randomised: a firewall must not assume 123 on both sides. NTPv4: Port Randomization	Proposed Standard	August 2021	updates 5905
RFC 9748	The protocol's IANA registries: useful to interpret registered extensions and values. Updating the NTP Registries	Proposed Standard	March 2025	updates 5905, 5906, 7821, 7822, 8573
RFC 9769	Interleaved modes, for more accurate timestamps: an advanced topic, not the basic client-server mode. NTP Interleaved Modes	Proposed Standard	May 2025	updates 5905

Ongoing work (monitoring, DHCPv6, new versions) consists of Internet-Drafts: they are not published standards. Follow them on the IETF NTP working group's documents page.

An RFC is not a regulatory obligation. Security frameworks ask for clock synchronisation, rarely for a protocol: neither ISO 27001 (control 8.17), PCI-DSS (10.6) nor DORA (RTS 2024/1774, Art. 12) mandates NTP, NTS or a stratum. Clause by clause: what each framework actually requires about time. To check a given server, over NTP and NTS: the online validator.

For whom? Why does it matter?

👤 Individuals

You don't have to do anything! Your devices are already configured. NTP ensures that your emails arrive with the correct timestamp, that your 2FA codes work, and that your photos are correctly dated.

🏢 Businesses

Consistent time is crucial for:

Security log correlation
Transactions and billing
Compliance (GDPR, PCI-DSS...)
Proxmox clusters and NTP synchronization on Proxmox VMs
MariaDB replication and Galera cluster — replication lag detection (Seconds_Behind_Master) and Galera certification depend on synchronized clocks between nodes

🏭 Industry

Industrial systems (SCADA, PLCs) require precise synchronization to coordinate manufacturing processes and ensure traceability.

🏦 Finance

Financial markets require microsecond-level timestamping. MiFID II mandates 100-microsecond accuracy for high-frequency trading.

Going further

The Speaking Clock — hear NTP "for real" — a free, phone-accessible audible demo of the Stratum 1 time discussed in this article.
Our NTP infrastructure since 2005 — how these theoretical concepts translate into 20+ years of real-world operation.

Free NTP Tools

Three independent tools to diagnose your time synchronization: