Diagnose DNS problem

[Paul Smith]

On Sun, 2022-10-02 at 16:19 +0100, Colin Law wrote:
> It is only this domain that doesn't work, others are ok.

Oh.  When you wrote:

> When I run, for a particular domain

it wasn't clear it failed for _only_ that domain but other domains
still worked.

If DNS works generally but not for one specific hostname, the problem
is not your DNS setup per se but rather with TTL (time-to-live) and
caching most likely: either at your local system or on your DNS server.

DNS TTL can be pretty long, sometimes, depending on the address.

You can flush your own cache, if you're using systemd-resolve, with
"sudo resolvectl flush-caches" (it's possible your older software won't
have this option; there may be some other option).  If that doesn't
work then the problem is your upstream DNS server has to timeout their
caches.  You can wait for it, or switch to a different server.