time.carvello.org
🇪🇺 🇩🇪 🇬🇧
Part of the NTP Pool Project (Global, Europe, DE)
Securely hosted in the EU using 100% renewable energy
Located in EU Central for low-latency access across Europe
Administered from London, United Kingdom
The CWS NTP Server
Our public time server synchronises with multiple stratum 1 upstream sources across four institutions in three countries, carefully selected for their reliability and proximity to our data centre, with primary timekeeping methods including atomic clocks, GPS and DCF77.
Our server operates at stratum 2, using the stratum 1 servers of the German National Metrology Institute (PTB) (Germany, atomic), the University of Erlangen-Nuremberg (Germany, GPS and DCF77), the Federal Institute of Metrology (METAS) (Switzerland, atomic), and CESNET (Czech Republic, atomic), plus a local fallback to maintain availability in the highly unlikely event of a full upstream outage.
The server is hosted on high-availability machines at Hetzner’s state-of-the-art, fully hydro-powered Falkenstein data centre in Germany, and typically maintains synchronisation within a few milliseconds of UTC. It is an active member of the NTP Pool Project's Global, European and German zones, and its location in the EU Central region enables us to provide low-latency access across Europe.
About Network Time Protocol (NTP)
Network Time Protocol (NTP) is used to keep computers and devices in sync with accurate time. It works over the internet or local networks, adjusting system clocks to match Coordinated Universal Time (UTC).
NTP has been in use since the 1980s and remains one of the core protocols of the internet. It helps ensure that systems around the world can maintain consistent time, which is essential for everything from logging and file timestamps to security and communication between systems.
The protocol typically uses UDP port 123 and works by exchanging time-stamped messages with trusted servers. It accounts for delays caused by the network and adjusts accordingly. Over the public internet, it can usually keep time accurate to within a few milliseconds. On local networks, precision can improve to under one millisecond.
Configuring Your Clients
Apple macOS
See Apple's guide, entering time.carvello.org as your network time server.
Cisco IOS and NX-OS
router# config t
Enter configuration commands, one per line. End with CNTL/Z.
router(config)# no ntp server
router(config)# ntp server time.carvello.org
router(config)# copy running-config startup-config
Juniper Jonos
NTP is configured at the [edit system ntp] hierarchy level:
system {
ntp {
server time.carvello.org;
}
}
Linux
Edit /etc/ntp.conf or /etc/chrony/chrony.conf (depending on the service you're using).
Remove or comment out any lines starting with server and add:
server time.carvello.com iburst
Restart the NTP/chrony daemon using sudo service ntp reload or sudo service chrony force-reload.
If you are instead using the stock systemd-timesyncd edit /etc/systemd/timesyncd.conf and set the content of the [Time] block to:
[Time]
NTP=time.carvello.org
Restart systemd-timesyncd using systemctl restart systemd-timesyncd.service as a user with appropriate permissions.
Microsoft Windows
Open the Control Panel.
Click the "Date and Time" icon.
Choose the "Internet Time" tab. (This will not be available if your PC is part of a domain. In that case, it will synchronize time with the domain controller. You can configure the controller to use Google Public NTP.)
Click the "Change settings..." button.
Check the box "Synchronize with an Internet time server".
Next to "Server:", enter time.carvello.org.
Microsoft Windows Server
See Microsoft's guide.
NTP Packet Format
Each NTP message is 48 bytes long and includes the following key fields:
Leap Indicator (2 bits): Warns of an upcoming leap second.
Version Number (3 bits): Indicates the NTP version in use.
Mode (3 bits): Describes the type of message (client, server, etc.).
Stratum (8 bits): Indicates the level of the server in the time hierarchy.
Poll Interval (8 bits): Suggests how often the client should query the server.
Precision (8 bits): Indicates the precision of the system clock.
Root Delay & Root Dispersion (32 bits each): Measure delays and uncertainties in the time source.
Reference Identifier (32 bits): Identifies the reference clock.
Timestamps (4 fields, 64 bits each):
Reference Timestamp: When the server clock was last updated.
Originate Timestamp: When the client sent the request.
Receive Timestamp: When the server received the request.
Transmit Timestamp: When the server sent the response.
These fields allow the client to calculate the round-trip delay and offset, ensuring accurate time adjustment.
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PLEASE NOTE
This service is offered without support, warranty, or guarantee. We are committed to respecting users' privacy, so minimal temporary logs are maintained to prevent abuse. Although the CWS NTP Time Server has inbuilt redundancy and is run on high-availability infrastructure, configuring fallback servers on your clients is always sensible - a list of popular public NTP servers is available here (note: Google's public NTP server uses a technique called 'leap smearing', which can cause compatibility issues when used alongside standard NTP servers such as ours). We enforce IP-level rate limiting for the purposes of load management and abuse prevention. Although our limits are generous and unlikely to be obtrusive in real-world use (even for decently sized NAT'd sites), you might encounter them or some initial throttling if you attempt to synchronise a very large number of computers in the same subnet with us all at once; in these situations, it can be beneficial to set up one or two local time servers that synchronise with us and then redistribute locally.
When configuring your clients, use the hostname of our server and not its IP addresses, since these are subject to change in the future.
