How does DNS propagation work

I split the topic so we can discuss the nature of DNS propagation while keeping the MyBB plugin topic clean.

I don’t see the relation.

Of course, servers exist at geographic relation, and there is correlation between geographic location and the latency to another server at another geographic location. But that latency is typically no more than a few hundred milliseconds, so it doesn’t explain why DNS changes can take days to take effect.

I wrote an article before explaining how DNS propagation works, so I won’t cover that in detail here:

In the most basic setup, the DNS Resolvers configured in your device (usually provided by your ISP) will directly contact the authoritative nameservers of your domain to fetch the records, and cache it. The reason DNS propagation is an issue is because the DNS resolver may be caching it for a long time.

This can get worse with tiered caching. If your own device caches the DNS results it obtains from your router, your router caches the DNS results from your ISP, and your ISP caches the DNS results from the authoritative nameservers, it can take a long time for all the caches to be updated with new information.

Geographic location is meaningless. Someone living next to the datacenter may be unable to access the website for weeks because their DNS resolver obtained results in the past, and really aggressively caches it, but someone on a different continent can see the website immediately because their DNS resolver did not have any records cached, or just doesn’t cache it for very long.

That’s also irrelevant. Whether someone is trying to look up or doesn’t matter.

For the custom domain, they will have to look up the authoritative nameservers of the domain with the .com nameservers, and then query those authoritative nameservers.

For the subdomains, they may have already cached which nameservers are responsible for, but to know where is hosted, they will have to query our nameservers first. Our nameservers will return the relevant IP for that subdomain, but they could just as well have delegated control to different nameservers entirely.