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My website is hosted by provider A. Due to contractual issues I was forced to move the domain to hoster B. B is the new registrar as well.

According to the whois entry the domain was successfully moved to B. Apparently, the DNS server have not updated yet, becasue the old servers are still accessible when typing www.mydomain.com in my browser.

However, when using services such as http://get-site-ip.com/ the retrieved IP points to hoster B. How is this possible? This would mean that the DNS server did update. But why can I still access the old servers with http?

Why are the servers of hoster A still accessible though the website's IP points to my new hoster.

null
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  • You use the definite article 'the' as if there was one DNS server; there are millions, although there _should_ be only two (or a handful) that are authoritative and those should update almost instantly, and the (many) others that have cached old data _should_ refresh at or before TTL as discussed in the answer. – dave_thompson_085 Feb 21 '17 at 13:17
  • What OS are you using? What DNS is configured? – 030 Feb 21 '17 at 22:17

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How is this possible?

Caching - (nearly) always caching.

When a DNS request is made, part of the response is the Time To Live(TTL) of the record. The upstream caching DNS server that serviced your request will have looking in it's cache to see if it had a record for example.com. It will have determined that the TTL had not expired and it will have served your request from it's cache.

When you went to get-site-ip.com there are 2 possibilities

  • it did not have had a record for example.com so it had to look it up.
  • it does not cache records and looked it up.

In both scenarios, it has to go to the DNS and request the records which are for your new server.

user9517
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  • You should probably add that it can take up to 48 hours for DNS to propagate after a change. It all depends on where the server is and how often the cached records are flushed on all the devices between wherever you are and wherever it is. The best thing you can do is on the old Pages put in a forward to the new one based on IP. – Rowan Hawkins Feb 21 '17 at 11:06
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    I refuse to propagate that apocrypha. – user9517 Feb 21 '17 at 11:14
  • Do you have an external source for that opinion? Every external dns provider I have worked with mentions the delay. I have seen it operationally by checking from geographically separated independent hosts. – Rowan Hawkins Feb 21 '17 at 11:21
  • My own testing when I recently moved some systems about. Everything either worked straight away because they had not recently looked up the relevant records or soon after the TTL expired the new addresses were picked up. That's the way the system is designed to work. Granted TTLs can be and are ignored but that's incorrect behaviour. The mantra of 48 hours is just that. – user9517 Feb 21 '17 at 11:28
  • And my comment is that those hosts that you're checking from are all geographically located in the same place. When I was checking this a few years ago I was checking from places in different countries across oceans. – Rowan Hawkins Feb 21 '17 at 11:32
  • No, the testing points were located all over the globe specifically .au, .hk, us California, and New York, .de and .fr for services in .gb and .ca. Can I suggest you go and refresh your understanding of DNS 'propagation'. It's not like ripples from a stone in a pond, it's entirely dependent on TTL and caching. – user9517 Feb 21 '17 at 11:40
  • I do agree with you that it should not take that long. The part of that is setting the correct customer expectation during the move. That is why I still use that "up to" delay figure. – Rowan Hawkins Feb 21 '17 at 11:42