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A comment on What happens when you update your DNS. Parent comment

Re:What happens when you update your DNS by fragmede on Monday June 22, 2020 @05:29PM (#23606957)
In particular, one your ISPs/their ISP's DNS servers may be caching a record for longer than it's supposed to and will return incorrect and expired data.

The other possibility is different IP's being returned by a DNS server based on where a query is coming from, eg a CDN. If you're in location A and your ISPs DNS server is in location B, the CDN's DNS server may return a different IP based on if the request is coming from A or B. ECS [0] is supposed to mitigate this, but may or may not be used.

[0] https://en.wikipedia.org/wiki/EDNS_Client_Subnet

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Re:What happens when you update your DNS by qes on Monday June 22, 2020 @05:58PM (#23607348)
> In particular, one your ISPs/their ISP's DNS servers may be caching a record for longer than it's supposed to and will return incorrect and expired data.

It's disturbing how many clients we'll see hitting an old IP address for 30 days after a change.

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