10

Anyone know how systemd-resolve voodo works?

192.168.1.30is the correct DNS server for my network, as returned by DHCP.

/etc/resolv.conf points to 127.0.0.53

Systemd claims to be using the correct server.

systemd-resolve --status | grep "DNS Servers"
192.168.1.30

But dig indicates it is not forwarding requests If I specify the server I can resolve shadowbox

dig @192.168.1.30 shadowbox

; <<>> DiG 9.16.1-Ubuntu <<>> @192.168.1.30 shadowbox
...

;; ANSWER SECTION:
shadowbox.      60  IN  A   192.168.1.34
...

systemd-resolve cannot

dig @127.0.0.53 shadowbox

; <<>> DiG 9.16.1-Ubuntu <<>> @127.0.0.53 shadowbox
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 60161
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 65494
;; QUESTION SECTION:
;shadowbox.         IN  A

;; Query time: 0 msec
;; SERVER: 127.0.0.53#53(127.0.0.53)
;; WHEN: Sun Jun 07 14:00:12 CEST 2020
;; MSG SIZE  rcvd: 38

I have tried bouncing the server, flusching acashed and mamually setting the server

systemd-resolve --flush-caches
systemd-resolve --set-dns=192.168.1.30 --interface=enp0s31f6

I can chattr +i /etc/resolv.conf to regain control of DNS, but it would be nice to know why systemd is not working, since I loose the benefits of DHCP.

muru
  • 207,228
teknopaul
  • 2,137

3 Answers3

3

Looks like this is by design. Pottering closed the issue https://github.com/systemd/systemd/issues/2514 with a wont-fix.

dig @127.0.0.53 shadowbox

systemd-resolved does not support simple names over DNS, only fqdn, and ignores the search directive.

teknopaul
  • 2,137
2

As hinted by @teknopaul (Jun 9, 2020 at 16:55) this has to do with resolved not resolving single-label domain names by default. I solved this same issue by creating the file /etc/systemd/resolved.conf.d/singlelabel.conf containing only

[Resolve]
ResolveUnicastSingleLabel=yes

Then single-label resolution works with the stub-resolver.

P.S.: Before making this change, the stub resolver had no problem resolving most of the single-label names on my LAN, which made this problem really hard to pin down.

Morten Lind
  • 21
0

To add specific upstream:

  • add upstream dns in /etc/systemd/resolved.conf

    [Resolve] DNS=192.168.1.123

  • restart service systemd-resolved restart

  • check with systemd-resolve --status

    Global DNS Servers: 192.168.1.123

To use DHCP provisioned DNS Server ( Since you stated in the comments that you want it to "just behave like normal" ) :

In the configuration file for local network interface (a file matching the name pattern /etc/systemd/network/*.network) either specify to obtain local DNS server address from DHCP server using DHCP= option:

[Network]
DHCP=yes

Also make sure resolvconf is not interfering:

systemd-resolved will work out of the box with a network manager using /etc/resolv.conf. No particular configuration is required since systemd-resolved will be detected by following the /etc/resolv.conf symlink. This is going to be the case with systemd-networkd or NetworkManager.

However, if the DHCP and VPN clients use the resolvconf program to set name servers and search domains (see openresolv#Users for a list of software that use resolvconf), the additional package systemd-resolvconf is needed to provide the /usr/bin/resolvconf symlink. Note: systemd-resolved has a limited resolvconf interface and may not work with all the clients, see resolvectl(1) for more information. (from archwiki )

Bash Stack
  • 171