Two identical DNS A posts - only one seems to work?

I manage my DNS on Netlify name servers. I switched servers yesterday (and pointed the A post to a different IPv4 address) and this morning I noticed my site was down. The reason was that no A post could apparently be found for the domain name. DNS checks from ultratools.com and mxtoolbox.com also confirmed this.

Could be a propagation thing I guess, after all it had only been about 20 hours since I deleted my previous A post and added the new one. But here is the weird thing. I just added an identical A post on the domain, and within minutes, the site was up, and all DNS check services confirmed that they could find the IP address. My new post has the exact same TTL (3600).

The domain name in question is woodbrand.se
And to be clear, I am NOT hosting the site on Netlify.

Two questions:

  1. WHY did this work? And can I safely delete one of these identical A posts? I don’t want to risk additional downtime.
  2. What is best practice in order to avoid DNS downtime when changing IP address? Should I add the new A post and wait a while before deleting the old one? This seems to be the only option since netlify does not let me modify an existing post, only delete it.

I don’t think the Netlify UI or any other DNS management lets you add 2 exactly same records.

Are you sure they’re 100% identical, that is no space, no character case, nothing is different?

@alexanderhall Welcome to the Netlify community.

The first trick to minimizing DNS propagation delays is to know what you are doing before you do it.

Other than that, does this information help:

It seems like you can. I just added 3 identical ones.

Whitespace could have been the issue, it’s hard to tell from the UI. I’m usually careful to not include whitespace but it’s possible I made mistake.

Oh yes, I just tried it and turns out you can add same record after all (even system records for that matter). I remembered this part showing me an error somewhere, probably it was my previous DNS provider.

As to why it was not working and why it started working, it’s hard to guess. Maybe it was a fluke or something else was wrong altogether?