On Wed, 2025-03-19 at 23:24 +0100, Patrick Dupre via users wrote:
> There is only one PC with a dongle.
> The question to get the contraol on the DNS server.
> Why when I just start the PC, I have
> 
> Link 9 (enp0s20f0u11)
>     Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6
>          Protocols: +DefaultRoute LLMNR=resolve -mDNS -DNSOverTLS 
> DNSSEC=no/unsupported
> Current DNS Server: 192.168.8.1
>        DNS Servers: 192.168.8.1 fe80::5044:fdff:fe85:29e3
> 
> 
> and 1 minute later
> Link 9 (enp0s20f0u11)
>     Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6
>          Protocols: +DefaultRoute LLMNR=resolve -mDNS -DNSOverTLS 
> DNSSEC=no/unsupported
> Current DNS Server: fe80::5044:fdff:fe85:29e3
>        DNS Servers: 192.168.8.1 fe80::5044:fdff:fe85:29e3

If you have more than one DNS server (and as far as it's concerned two
different addresses for the same server are two servers), standard
behaviour *was* always to try the first one, then only try the second
one if the first one didn't respond (if it responds, but doesn't have
the answer it has still responded, and the second server is not
consulted).  Every time there's a DNS query, it'll poll the first
server, first.

Other systems (and I don't know if Fedora does this now) may switch
over to the second server if the first one didn't respond, and continue
to use it as first choice.  Only switching back if the *now* first
server doesn't respond.

> which does not let me having a connection to the rest of the world while it 
> was OK just before?
> It seems to be due to IPV6.
> 
> Do I need to switch IPV6 from automatic to
> Disable or Automatic DHCP, manual ?
> or set the IPV6 DNS
> 
> Note that with the working dongle, I have
>     Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6
>          Protocols: +DefaultRoute LLMNR=resolve -mDNS -DNSOverTLS 
> DNSSEC=no/unsupported
> Current DNS Server: 192.168.1.1
>        DNS Servers: 192.168.1.1

If you want to force a specific server, then set your DHCP client
options to use the DNS server you specify and not get it from DHCP.

The "automatic DHCP addresses only" choice will only get your IP
address from the DHCP server, you will set your DNS server and it won't
change it.

You could be having IPv6 issues that may need you to disable it, or
configure it in a specific way.  I could hazard a guess that your IPv4
connection should have an IPv4 address for a DNS server and your IPv6
connection should have an IPv6 address for its DNS server.  It may be a
simple way that ensures least confusion and your IPv4 queries get IPv4
answers, your IPv6 queries only get IPv6 answers.

I really can't test IPv6 here, the ISPs support for it is erratic.

-- 
 
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Linux 3.10.0-1160.119.1.el7.x86_64 #1 SMP Tue Jun 4 14:43:51 UTC 2024 x86_64
 
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