Diagnose DNS problem

[Colin Law]

It has gone again when I try this morning.

On Sun, 2 Oct 2022 at 18:12, Paul Smith <paul at mad-scientist.net> wrote:
>
> 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.

Sorry I wasn't clear enough, though I did say a couple of lines later
DNS seems to work ok on all other domains that I have tried.

>
> 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"

The resolvectl command is not present, but I found suggestions that
this should work
sudo systemd-resolve --flush-caches
I tried that but it did not make any difference.

The host command for the domain fails, but if I use that command and
tell it to use 8.8.8.8 then it works,
Also I have now been able to test it with a phone connected to the
same router and it also fails, which tells me that it is a problem
with the router or the ISP.  I will setup the connection to use
8.8.8.8 and hopefully that will sort it.

Colin