The DNS issue seems related to my local network setup: I am connected to the wider internet via a FritzBox with local address 192.168.178.1 and the Turris Omnia connected as 192.168.178.20.
My Arch Linux system is behind the Turris Omnia and sees the Turris Omnia as 192.168.1.1. The Arch Linux machine has IPv4 address 192.168.1.164
In the status overview I see
IPv4 WAN Status
eth1 Type: dhcp
Address: 192.168.178.20
Netmask: 255.255.255.0
Gateway: 192.168.178.1
DNS 1: 192.168.178.1
Expires: 9d 23h 42m 30s
Connected: 0h 17m 30s
IPv6 WAN Status
eth1 Address: 2001:985:d31:1:da58:d7ff:fe00:43f0/64
Gateway: fe80::9ec7:a6ff:fec7:cbcb
DNS 1: fd00::9ec7:a6ff:fec7:cbcb
Connected: 0h 17m 5s
I have the impression that when switching from a wired connection via the Turris Omnia to a WIFI connection via the Fritzbox (as 192.168.178.22 – my Turris Omnia does not provide WIFI) these IPv4 and IPv6 statuses get messed up.
So I am wondering if I need to adapt my DHCP and DNS settings to handle this dual reality.
Probably I also need to learn more about local networks and subnets… Any suggestions on where I can read up on this issue are most welcome.