Diagnose DNS problem

[Colin Law]

On Sun, 2 Oct 2022 at 15:35, Paul Smith <paul at mad-scientist.net> wrote:
> ...
> Then it appears that maybe your router's DNS server is wonky.
>
> To tell you can use the "host" command; if you don't give it a DNS
> server it will use the system one:
>
>   $ host www.google.com
>   www.google.com has address 142.251.35.164
>   www.google.com has IPv6 address 2607:f8b0:4006:81e::2004
>
> If you do give it a DNS server it will use that specifically:
>
>   $ host www.google.com 192.168.1.254
>
> Does that return something useful?
>
> You can also try using one of the public DNS servers; for example
> Google provides some very nice ones:
>
>   $ host www.google.com 8.8.8.8
>   Using domain server:
>   Name: 8.8.8.8
>   Address: 8.8.8.8#53
>   Aliases:
>
>   www.google.com has address 172.217.165.132
>   www.google.com has IPv6 address 2607:f8b0:4006:80c::2004
>
> Does that work?
>

It is only this domain that doesn't work, others are ok.

After fiddling about with various varieties of the host command it has
suddenly started working again, though rebooting both the router and
the PC did not work earlier.  I guess it must have been a caching
problem of some sort, possibly ISP related.  At least I now know more
about how to investigate such problems so if it reappears I will have
some ideas on what to try.  I don't know whether other devices showed
the problem as there isn't anything to try it with at the location.

Thanks

Colin