domain name resolution with systemd-resolved

apex8 · 2018-06-12 12:07:02

Hi,

I have a setup where my network is configured completely via systemd. However I wasn´t able to access windows clients via their domain name. So to enable this I installed samba and added wins to /etc/nsswitch.conf. My hosts line looked like this:

hosts: files mymachines resolve [!UNAVAIL=return] dns wins myhostname

However pinging windows clients via domain name still didn´t work. I tried to remove the part 'resolve [!UNAVAIL=return]' and then it worked, so systemd-resolved might be configured wrong.
My /etc/resolv.conf is now symlinked from /run/systemd/resolve/resolv.conf. I also disabled dhcpcd. My current hosts line in nsswitch.conf looks like this:

hosts: files mymachines resolve  wins myhostname

I removed 'dns' as I read here that 'resolve' is intended to replace dns (However its still in the base config which is deliverd by arch) and I also removed the [!UNAVAIL=return] after resolve. With [!UNAVAIL=return] in place every ping to a NetBios name results in an 'Name or service not known'.

So everything at least seems to work now, but still I would like to know if this configuration is correct or if I forgot something that might lead to some bad surprises in the future.

Thanks and best regards
apex

Last edited by apex8 (2018-06-12 12:12:38)

lo1 · 2018-06-12 16:04:19

man nss-resolve:

it is recommended to place "resolve" early in
       /etc/nsswitch.conf's "hosts:" line (but after the "files" or "mymachines"
       entries), right before the "dns" entry if it exists, followed by
       "[!UNAVAIL=return]", to ensure DNS queries are always routed via systemd-
       resolved(8) if it is running, but are routed to nss-dns if this service is not
       available.

Most likely that you were right and systemd-resolved is not configured properly? What's the output of `systemctl status systemd-resolved` and `cat /etc/systemd/resolved.conf`.

See also https://wiki.archlinux.org/index.php/Do … d-resolved

apex8 · 2018-06-13 06:42:50

Thanks for your reply! Here's my output:

systemctl status systemd-resolved

● systemd-resolved.service - Network Name Resolution
   Loaded: loaded (/usr/lib/systemd/system/systemd-resolved.service; enabled; vendor preset: enabled)
   Active: active (running) since Wed 2018-06-13 08:24:45 CEST; 8min ago
     Docs: man:systemd-resolved.service(8)
           https://www.freedesktop.org/wiki/Software/systemd/resolved
           https://www.freedesktop.org/wiki/Software/systemd/writing-network-configuration-managers
           https://www.freedesktop.org/wiki/Software/systemd/writing-resolver-clients
 Main PID: 347 (systemd-resolve)
   Status: "Processing requests..."
    Tasks: 1 (limit: 4915)
   Memory: 1.6M
   CGroup: /system.slice/systemd-resolved.service
           └─347 /usr/lib/systemd/systemd-resolved

Jun 13 08:24:45 avv-pc-10 systemd[1]: Starting Network Name Resolution...
Jun 13 08:24:45 avv-pc-10 systemd-resolved[347]: Positive Trust Anchors:
Jun 13 08:24:45 avv-pc-10 systemd-resolved[347]: . IN DS 19036 8 2 49aac11d7b6f6446702e54a1607371607a1a41855200fd2ce1cdde32f24e8fb5
Jun 13 08:24:45 avv-pc-10 systemd-resolved[347]: . IN DS 20326 8 2 e06d44b80b8f1d39a95c0b0d7c65d08458e880409bbc683457104237c7f8ec8d
Jun 13 08:24:45 avv-pc-10 systemd-resolved[347]: Negative trust anchors: 10.in-addr.arpa 16.172.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 168.192.in-addr.arpa d.f.ip6.arpa corp home internal intranet lan local private test
Jun 13 08:24:45 avv-pc-10 systemd-resolved[347]: Using system hostname 'avv-pc-10'.
Jun 13 08:24:45 avv-pc-10 systemd[1]: Started Network Name Resolution.

I haven´t done any adjustments to /etc/systemd/resolved.conf, because using by dhcp (via systemd-networkd) a nameserver is found and network is working. Also I have found here that there may be cases when removing "[!UNAVAIL=return]" fixes issues. Unfortunately there are no reasons given.

cat /etc/systemd/resolved.conf

#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.
#
# Entries in this file show the compile time defaults.
# You can change settings by editing this file.
# Defaults can be restored by simply deleting this file.
#
# See resolved.conf(5) for details

[Resolve]
#DNS=
#FallbackDNS=8.8.8.8 8.8.4.4 2001:4860:4860::8888 2001:4860:4860::8844
#Domains=
#LLMNR=yes
#MulticastDNS=yes
#DNSSEC=no
#Cache=yes
#DNSStubListener=udp

systemd-resolved --status

Global
          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 2 (enp0s31f6)
      Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6
       LLMNR setting: yes
MulticastDNS setting: no
      DNSSEC setting: no
    DNSSEC supported: no
         DNS Servers: xxx.xxx.xxx.xx #correct dns server IP

Arch Linux

#1 2018-06-12 12:07:02

domain name resolution with systemd-resolved

#2 2018-06-12 16:04:19

Re: domain name resolution with systemd-resolved

#3 2018-06-13 06:42:50

Re: domain name resolution with systemd-resolved

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