So, I was on this website that changed server (DNS update). So it was unavailable for a while. It was supposed to last a few hours, but then I still couldn’t access it. The error message said that it takes some time for the updates to take effect worldwide. I live in Europe.
Something weird happened this morning. I went to the site and could finally access it fine. It all worked. But a few hours later, that error message turned up again.
Is that normal? Do the DNS updates take time to take the full effect, so they may work for a while and then stop before it is complete? Some sources say it may take up to 24 hours, but it may take up to 48 or 72 hours by now. It’s been little less than 24 hours by now.
My guess is your ISP didn’t do a great job setting up their DNS servers. They probably have a few to handle lookups from customers and use separate caches, so some servers were updated for the new site info and others weren’t. In such a scenario, it would essentially be chance whether or not you connected to the site.
(I’m making a lot of assumptions here. What you’re seeing isn’t normal, but it isn’t too unusual either.)
Typically the estimate they provide is that it takes up to 24 hours, but in my experience it always propagates in an hour or so.
Sometimes providers use what’s known as round-robin DNS resolution, so potentially you could hit one DNS server that’s updated, and later hit one that isn’t yet updated.
There are a lot of complex scenarios where it could break like this, but one very easy way it could break is that they pushed the first update, then realized there was a problem with it, so they pushed a second update.
It depends on how the Time to Live values are configured in the DNS record. I once had a domain which was (mis?) configured with a TTL of two weeks. When I moved my domain to a different server, it was a major pain in the ass because some people were still resolving to the old server for two weeks.
DNS errors happen all the time. You don’t hear about it unless an entire country drops off the net, or HK is mysteriously routed through mainland China for a while, but for every enormous error there are several tiny errors.
The system of updating DNS records for big DNS servers (zone updates) runs entirely separate to and crosswise to the system for updating individual values like a server address. If a DNS server gets a new zone update which contains old values, it can temporarily loose the new value.
And no, it isn’t ‘normal’. It just happens sometimes, for the same reason that round-robin systems sometimes give the wrong value: the new value takes a while to propagate through the system, and while it propagates, some of the servers have old values.
My personal impression is that propagation delays and errors used to happen much more commonly than they do now.
Former DNS admin here. Yeah, it’s almost certainly the Time to Live (TTL) value that’s causing the issue the OP is observing. It determines how long the caching DNS server is supposed to hold the record before it forgets the entry and asks the authoritative DNS server for the domain what the record resolves to again.
Now, your ISP may give you one or two IP addresses to use as a caching DNS server, but those IPs usually are load balanced across more servers. Each DNS server operates fairly independently, and the TTL one has remaining in its cache for a certain domain isn’t going to be the same as the other members of the DNS server cluster - it depends on when that particular server last had to look up that record. So, you ask your DNS server for what the record resolves to, and depending on whether the TTL has expired on the server that answers, it could respond with the old one record or the new record.
1.1.1.1
1.0.0.1
There are other specialist services like Unlocator, which changes your geolocation for specific sites. QuickSetDNS is a nice little Windows utility that let’s you quickly and painlessly switch from one DNS server to another.