(originally was a forum post https://bbs.archlinux.org/viewtopic.php?id=256979, but after editing it a few times and adding to it, I realise it's probably a bug)

I am using NetworkManager & systemd-resloved in their default configuration.

/etc/resolv.conf is a symlink to /run/systemd/resolve/stub-resolv.conf

As it should, NetworkManager reports in the logs when it starts:

dns-mgr[0x55f2a8093240]: init: dns=systemd-resolved rc-manager=symlink, plugin=systemd-resolved

Which is what I want.

NetworkManager correctly picks-up the right DNS server from DHCP

NetworkManager[19709]: <info> [1593431290.2268] dhcp4 (enp0s13f0u3u3): option domain_name_servers => '192.168.199.1'

But it doesn't detect that there is a change with the running configuration:

dns-mgr: (device_ip_config_changed): queueing DNS updates (1)
dns-mgr: (device_ip_config_changed): DNS configuration did not change
dns-mgr: (device_ip_config_changed): no DNS changes to commit (0)

But then, systemd-resolved keeps on using the fallback DNS server:

$ systemd-resolve --status
Global
LLMNR setting: yes
MulticastDNS setting: yes
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Current DNS Server: 8.8.8.8
Fallback DNS Servers: 1.1.1.1
9.9.9.10
8.8.8.8
2606:4700:4700::1111
2620:fe::10
2001:4860:4860::8888
DNSSEC NTA: 10.in-addr.arpa
16.172.in-addr.arpa
168.192.in-addr.arpa
17.172.in-addr.arpa
18.172.in-addr.arpa
19.172.in-addr.arpa
20.172.in-addr.arpa
21.172.in-addr.arpa
22.172.in-addr.arpa
23.172.in-addr.arpa
24.172.in-addr.arpa
25.172.in-addr.arpa
26.172.in-addr.arpa
27.172.in-addr.arpa
28.172.in-addr.arpa
29.172.in-addr.arpa
30.172.in-addr.arpa
31.172.in-addr.arpa
corp
d.f.ip6.arpa
home
internal
intranet
lan
local
private
test

Link 12 (enp0s13f0u3u3)
Current Scopes: LLMNR/IPv4 LLMNR/IPv6
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no

Link 2 (wlp0s20f3)
Current Scopes: LLMNR/IPv4 LLMNR/IPv6
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no

Which https://www.dnsleaktest.com/ confirms.

If I manually set the DNS server for the interface with resolvectl, it works and the correct entries are reported in the status.