NTP and NTS: frequently asked questions

Three at least, four ideally. The reason is mathematical: with a single source you cannot tell that the time is wrong. With two that disagree you cannot tell which one is right. With three, if one goes bad the other two still agree and the bad one is discarded.

Configure this server as one of your sources, not as your only source.

The packet format is the same; the difference is what the client does with it. SNTP takes one measurement and sets the clock from it. A real NTP client (chrony, ntpd) measures several sources continuously, filters the measurements, looks for agreement between the sources, and learns and corrects the frequency error of the clock.

From the server side the two look identical. On your servers, use a full NTP client, not SNTP.

We do not smear them. Clients receive the standard leap indicator.

That is why servers that do smear (time.google.com, time.cloudflare.com) are deliberately absent from our upstream list. You should not mix smearing and non-smearing sources either: on a leap second day the two groups drift apart relative to each other, and your client may declare them mutually false and stop synchronising altogether.

It gives you a rough idea, not a precise figure. The measurement is made over HTTP: six requests are sent and the one with the shortest round trip is chosen — a simple analogue of NTP's own filtering logic, and noticeably more accurate than averaging. Server time is read at millisecond resolution.

Even so, TCP/TLS latency, browser timer resolution and asymmetric paths leave a few milliseconds of uncertainty. For a real figure, measure with an NTP client: chronyd -Q 'server ntp.alastyr.com iburst'

It is kept from drifting. The displayed time is your device's clock plus the measured offset, and the offset is re-measured once a minute. The page stays in step with the server however long you leave it open.

But this is only a display — having the page open does not correct your device's system clock. For that you need to configure an NTP client.

Yes. NTS-KE is open on TCP 4460 and the certificate is a publicly verifiable TLS certificate. See the NTS section for usage.

We also connect to most of our own upstream sources over NTS — so our chain is authenticated not only down to us, but above us as well.

Being stratum 1 requires a GPS/GNSS receiver and PPS hardware physically attached to the server. This server has no such hardware.

But stratum is not a quality grade — it is a measure of distance from the reference. A well-connected stratum 2 can serve more accurate time than an overloaded or distant stratum 1. Real quality is measured by root delay, root dispersion and jitter — all three are published live in the status section.

No. Türkiye has used UTC+03:00 all year round since 2016; clocks are not moved.

If your system's time zone is set to Europe/Istanbul and your tzdata package is current, it behaves correctly. Older tzdata releases may still try to apply daylight saving — if you see a one-hour shift twice a year, that is the first place to look.

Yes — 2a06:ad40:0:1::90. Both NTP (123/udp) and NTS-KE (4460/tcp) work over IPv6, and forward and reverse (PTR) DNS records are consistent.

If you use the hostname, your client will pick whichever is appropriate.

Both are valid, and mixing them is best. This server is registered with the pool.ntp.org project, so writing tr.pool.ntp.org may already land you here — but the pool returns different servers on every query and you cannot know in advance which one you will get.

Naming ntp.alastyr.com directly has two advantages: the address is fixed, and you can connect with NTS authentication, which pool addresses do not support. Our recommendation: configure us directly as one source, and add a couple of pool addresses alongside for diversity.

Yes, that is what it is for. But the service is provided as is, with no legal guarantee.

On critical systems always configure several independent sources — do not depend on this server, or on any single server, alone. If you need legally traceable timestamps, approach TÜBİTAK UME's relevant services directly.