Ubuntu – Wrong nameserver set by resolvconf and NetworkManager

17.10dhcpdnsnetworking

My DNS server is 192.168.1.152.

This DNS is provided to clients by DHCP. The windows clients on my LAN resolve names properly using that DNS, but my Ubuntu VM doesn't.

The VM is set up with bridge networking and is being properly provided the DNS server, but my local hostnames aren't being resolved by nslookup or browsers.

Here is an nslookup of one of my local domains:

# nslookup unraid.local
Server:     127.0.0.53
Address:    127.0.0.53#53

** server can't find unraid.local: SERVFAIL

Here is what it should resolve by using my DNS server:

# nslookup unraid.local 192.168.1.152
Server:     192.168.1.152
Address:    192.168.1.152#53

Name:   unraid.local
Address: 192.168.1.152

/etc/resolv.conf has a wrong nameserver:

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
# 127.0.0.53 is the systemd-resolved stub resolver.
# run "systemd-resolve --status" to see details about the actual nameservers.

nameserver 127.0.0.53

I ran that command. Under DNS Servers, confusingly, it specifies the correct server (and my default gateway).

root@ubuntu:~# systemd-resolve --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 (ens33)
      Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6
       LLMNR setting: yes
MulticastDNS setting: no
      DNSSEC setting: no
    DNSSEC supported: no
         DNS Servers: 192.168.1.152
                      192.168.1.1

I don't want to "hard code" the DNS server's IP in a config file because I won't be able to resolve when I change networks.

How can I get resolvconf and NetworkManager to automatically set the DHCP server's IP in /etc/resolv.conf?

Best Answer

Known systemd bug.

Temporary workaround with no need to reconfigure if the DNS IP's changes:

sudo rm -f /etc/resolv.conf
sudo ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf
reboot

Related Solutions

Ubuntu – How to set a static DNS nameserver address on Ubuntu Server

1: Resolvconf writes its dynamic resolv.conf file at /run/resolvconf/resolv.conf. /etc/resolv.conf is a symbolic link to the latter location. If you want to use a static resolv.conf file, simply replace the /etc/resolv.conf symbolic link with a file. This is currently supported but not recommended.

2: As I understand it, the affected machine is running Ubuntu Server edition. In that case it configures interfaces using the ifup program whose configuration file is /etc/network/interfaces. For interfaces configured via the dhcp method, ifup (normally) uses dhclient from the isc-dhcp-client package. Dhclient receives nameserver information from the DHCP server and its hook script /etc/dhcp/dhclient-enter-hooks.d/resolvconf sends this information to resolvconf which puts it into resolv.conf.

One thing you can do is edit /etc/resolvconf/interface-order such that eth0.dhcp comes before eth0.dhclient. (I assume that the relevant interface is eth0.) If you have the default interface-order you can, for example, just add a line eth0.dhcp before the line eth*.

--- interface-order_ORIG    2012-11-06 10:12:47.630529145 +0100
+++ interface-order 2012-11-06 10:13:16.410529800 +0100
@@ -9,6 +9,7 @@
 hso*
 em+([0-9])?(_+([0-9]))*
 p+([0-9])p+([0-9])?(_+([0-9]))*
+eth0.dhcp
 eth*
 ath*
 wlan*

Then add a dns-nameservers line to the iface eth0 stanza in /etc/network/interfaces with the correct nameserver address.

iface eth0 inet dhcp
    dns-nameservers 1.2.3.4

Because eth0.dhcp comes before eth0.dhclient, the correct nameserver address will be included in resolv.conf before the incorrect one.

Another way to override the unwanted behavior of including the DHCP-server-provided nameserver address is to edit the dhclient hook script. E.g., you can add a line like the following (where 1.2.3.4 is a nameserver address you would like to discard).

--- resolvconf_ORIG 2012-03-29 22:37:14.000000000 +0200
+++ resolvconf  2012-11-05 20:53:33.312681077 +0100
@@ -54,6 +54,7 @@
            fi
            shopt -s nocasematch
            for nameserver in $new_dhcp6_name_servers ; do
+               [ "$nameserver" = "1.2.3.4" ] && continue

Yet another possibility (a slightly crude one, since it's completely static) is to add a nameserver option to /etc/resolvconf/resolv.conf.d/head.

3: Setting DNS nameserver addresses has gotten more complicated because machines are becoming mobile, are getting more and more interfaces and static configuration is gradually being replaced by autoconfiguration.

Ubuntu – DNS at systemd’s 127.0.0.53 is ignoring some lookups

I found the fix that worked for me.

my resolv.conf file was pointing to the wrong place. This seems like a bug in Ubuntu as it happened on my laptop (the machine I first noticed this issue on) and on a fresh install of Ubuntu 18.04 Server.

The Default

$ ls -l /etc/resolv.conf

lrwxrwxrwx 1 root root 39 Apr 26 12:07 /etc/resolv.conf -> ../run/systemd/resolve/stub-resolv.conf

I deleted this and pointed to the correct file. After rebooting, this solved my issue. And I was even able to switch networks on my laptop and the DNS switched correctly. Of course when on external networks I can't resolve any of my local machines but that is expected. As soon as I switch back to my local network, all the local machines resolve correctly because my router is the DNS.

The Fix

$ sudo rm -f /etc/resolv.conf
$ sudo ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf
$ ls -l /etc/resolv.conf

lrwxrwxrwx 1 root root 32 May 29 08:48 /etc/resolv.conf -> /run/systemd/resolve/resolv.conf

$ sudo reboot

After that, everything worked as I expected and 127.0.0.53 is no longer being used at all.

The Correct Results

$ nslookup web1

Server:     192.168.1.1
Address:    192.168.1.1#53

Name:   web1
Address: 192.168.1.107

$ nslookup google.com

Server:     192.168.1.1
Address:    192.168.1.1#53

Non-authoritative answer:
Name:   google.com
Address: 172.217.7.174
Name:   google.com
Address: 2607:f8b0:4004:80e::200e

Best Answer

Related Solutions

Ubuntu – How to set a static DNS nameserver address on Ubuntu Server

Ubuntu – DNS at systemd’s 127.0.0.53 is ignoring some lookups

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