1

Yesterday I made some changes to the Name Server records for a clients domain.

Here's a link to a DNS propagation checker that shows the updated NS fields for only three DNS servers across the world.

I understand that DNS settings are cached & take some time, but it's been over 15 hours at this point & I've never quite seen a DNS behave so slowly. Normally I take even one server showing the updated settings as a sign that the rest are soon to come and in fact that's what I told my client, but obviously something isn't quite right.

Does anyone have any ideas? Right now I'm going through and just updating the DNS to nonsense values & then right back to maybe force them to recache, but I'm not confident in this method after seeing this happen.

little tiny man
  • 111
  • 3
  • Check the TTL you are using. Allow 2 times TTL for things to propagate. You should reduce the TTL well before making changes. – BillThor Oct 18 '17 at 23:22

1 Answers1

4

DNS doesn't propagate. There's no reason those name servers would have the name server information for the domain name you supplied unless a DNS client of those name servers asked them to resolve DNS records for the domain... or the DNS propagation checker asked them to query for the name servers of the domain name you supplied.

So it seems to me that what those DNS propagation checkers are actually doing is querying each of the listed name servers for the domain name you supplied, thereby forcing those name servers to query for the name servers for the domain name you supplied, thereby caching that information at those listed name servers.

DNS servers don't cache the whole of the entire DNS namespace nor do they cache all of the name servers for all of the registered domain names. Imagine if they did? What kind of scale would be needed to handle a database of that size and that type of workload, especially considering the near constant change to DNS records for all registered domain names in a single day? My name servers know nothing about your name servers or your DNS records until I ask my name servers to resolve a DNS record for your domain. Your name servers and DNS records don't get "propagated" to my name servers at any point. My DNS client makes a request of my name servers for a DNS record in your domain and my name servers then work to answer that query. Only then will my name servers have any information whatsoever about your name servers and domain name.

Using a DNS propagation checker may seem like a good way to check that your name server information is being found correctly, but propagation isn't what's being checked. The listed name servers are querying for the name server information for the domain name you supply and if the name servers are found then you get the big green check mark. It's a good test to see if your name server information can be found, but calling it a DNS propagation check is propagating (no pun intended) a myth about how DNS works. As you've seen though, those checkers can mask other problems... without giving you any clue as to what those problems may be.

joeqwerty
  • 108,377
  • 6
  • 80
  • 171