Did check this morning my /etc/resolve.conf and was surprised what I found in it:
# Generated by NetworkManager
search kpn lan
nameserver 192.168.2.254
In the past I had installed dnscrypt-proxy and that is still running. It needs nameserver 127.0.0.1 in resolve.conf and I know I had to do something to make sure resolve.conf was not overwritten. I checked my notes and see I had then to add NETCONFIG_DNS_POLICY="" to /etc/sysconfig/network/config. At that time I checked and things worked.
So it looks meanwhile things changed and NetworkManager took over resolve.conf
Searched the Internet and found you could prevent NetworkManager managing DNS by editing /etc/NetworkManager/NetworkManager.conf but I do not have that file, I have the /etc/NetworkManager/conf.d directory but that is empty. Reading “man NetworkManager.conf” it seems that is no problem and configuration can be done using files in conf.d
# cat /etc/NetworkManager/conf.d/do_not_touch_dns
[main]
dns=none
rc-manager=unmanaged
Restarted the network using sudo systemctl restart network but resolv.conf is still overwritten.
Could not find it in the documentation but renamed the file so it has a .conf extension and changed the access rights to 600
$ sudo mv /etc/NetworkManager/conf.d/do_not_touch_dns /etc/NetworkManager/conf.d/do_not_touch_dns.conf
$ sudo chmod 600 /etc/NetworkManager/conf.d/do_not_touch_dns.conf
$ ls -l /etc/NetworkManager/conf.d/do_not_touch_dns.conf
-rw------- 1 root root 37 May 8 10:20 /etc/NetworkManager/conf.d/do_not_touch_dns.conf
And now resolve.conf is no longer touched again.
Problem solved.