---
title: "Why does the time synchronization with my NTP server not work?"
slug: "why-does-the-time-synchronization-with-my-ntp-server-not-work"
updated: 2026-05-27T12:03:07Z
published: 2026-05-27T12:03:07Z
canonical: "docs.insys-icom.com/why-does-the-time-synchronization-with-my-ntp-server-not-work"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://docs.insys-icom.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Why does the time synchronization with my NTP server not work?

If the settings on your router are otherwise correct, please check the **NTP version** used by your NTP server. Our firmware uses **NTPv4**, which is backwards compatible with **NTPv3**. However, some **NTPv3** server implementations, such as Windows 10 servers, **only** accept **NTPv3** headers and time synchronization with such servers is not possible.

*Please, contact your NTP server manufacturer to find out if this applies to you.*

If your router is behind an external firewall and you are not using a local time server, UDP port 123 must be opened for the router for time synchronization.