Disconnecting and reconnecting docking station breaks DNS

[Nico Orrù]

I'm not sure which package this bug should be submitted to as service troubleshooting in the latest few Ubuntu releases is a jumbled mess.

Anyway, here's how to repro the problem:
- Lenovo Carbon X1 2016 (4th gen), OneLink+ docking station
- Ethernet connected to docking station
- Disconnect docking station
- Reconnect docking station

From this point on all DNS requests fail. Workarounds I found so far:
- reboot the machine (not really a solution)
- sudo system network-manager restart (requires sudo access)
- usually in older releases I'd just poke around with the resolver config files, but anything I do seems to be ignored now so I gave up and posted a bug instead.

Here's the journalctl log for NetworkManager, followed by an example of the problem:

nico@nico-lenovo-ubuntu:~$ journalctl -u NetworkManager -f
-- Logs begin at Sun 2017-02-19 00:10:56 GMT. --
Feb 20 20:22:41 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622161.9976] dns-mgr: Writing DNS information to /sbin/resolvconf
Feb 20 20:22:42 nico-lenovo-ubuntu dnsmasq[6728]: setting upstream servers from DBus
Feb 20 20:22:42 nico-lenovo-ubuntu dnsmasq[6728]: using nameserver 194.168.4.100#53(via lan1)
Feb 20 20:22:42 nico-lenovo-ubuntu dnsmasq[6728]: using nameserver 194.168.8.100#53(via lan1)
Feb 20 20:22:42 nico-lenovo-ubuntu dnsmasq[6728]: using nameserver 194.168.4.100#53(via wifi0)
Feb 20 20:22:42 nico-lenovo-ubuntu dnsmasq[6728]: using nameserver 194.168.8.100#53(via wifi0)
Feb 20 20:22:42 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622162.0156] device (wifi0): Activation: successful, device activated.
Feb 20 20:22:42 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622162.0169] manager: startup complete
Feb 20 20:22:43 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622163.1408] manager: WiFi hardware radio set enabled
Feb 20 20:22:43 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622163.1409] manager: WWAN hardware radio set disabled
Feb 20 20:27:40 nico-lenovo-ubuntu dhclient[6736]: receive_packet failed on lan1: Network is down
Feb 20 20:27:40 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622460.1588] manager: NetworkManager state is now CONNECTED_LOCAL
Feb 20 20:27:40 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622460.1589] manager: NetworkManager state is now CONNECTED_GLOBAL
Feb 20 20:27:40 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622460.1590] policy: set 'Auto ITADINANTA' (wifi0) as default for IPv4 routing and DNS
Feb 20 20:27:40 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622460.1590] device (lan1): state change: activated -> unmanaged (reason 'removed') [100 10 36]
Feb 20 20:27:40 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622460.1594] dhcp4 (lan1): canceled DHCP transaction, DHCP client pid 6736
Feb 20 20:27:40 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622460.1595] dhcp4 (lan1): state changed bound -> done
Feb 20 20:27:40 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622460.1618] dns-mgr: Writing DNS information to /sbin/resolvconf
Feb 20 20:27:40 nico-lenovo-ubuntu dnsmasq[6728]: setting upstream servers from DBus
Feb 20 20:27:40 nico-lenovo-ubuntu dnsmasq[6728]: using nameserver 194.168.4.100#53(via wifi0)
Feb 20 20:27:40 nico-lenovo-ubuntu dnsmasq[6728]: using nameserver 194.168.8.100#53(via wifi0)
Feb 20 20:27:40 nico-lenovo-ubuntu NetworkManager[6715]: <error> [1487622460.1799] platform-linux: do-change-link[5]: failure changing link: failure 19 (No such device)
Feb 20 20:27:40 nico-lenovo-ubuntu NetworkManager[6715]: <warn> [1487622460.1800] device (lan1): failed to disable userspace IPv6LL address handling
Feb 20 20:27:40 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622460.1803] devices removed (path: /sys/devices/pci0000:00/0000:00:14.0/usb2/2-4/2-4.1/2-4.1.3/2-4.1.3:2.0/net/lan1, iface: lan1)
Feb 20 20:27:56 nico-lenovo-ubuntu NetworkManager[6715]: <warn> [1487622476.6972] device (eth0): failed to find device 6 'eth0' with udev
Feb 20 20:27:56 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622476.6990] manager: (eth0): new Ethernet device (/org/freedesktop/NetworkManager/Devices/4)
Feb 20 20:27:56 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622476.7679] device (eth0): interface index 6 renamed iface from 'eth0' to 'lan1'
Feb 20 20:27:56 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622476.7742] devices added (path: /sys/devices/pci0000:00/0000:00:14.0/usb2/2-4/2-4.1/2-4.1.3/2-4.1.3:2.0/net/lan1, iface: lan1)
Feb 20 20:27:56 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622476.7742] device added (path: /sys/devices/pci0000:00/0000:00:14.0/usb2/2-4/2-4.1/2-4.1.3/2-4.1.3:2.0/net/lan1, iface: lan1): no ifupdown configuration found.
Feb 20 20:27:56 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622476.7745] device (lan1): state change: unmanaged -> unavailable (reason 'managed') [10 20 2]
Feb 20 20:27:56 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622476.7752] device (lan1): link connected
Feb 20 20:27:56 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622476.7801] device (lan1): state change: unavailable -> disconnected (reason 'none') [20 30 0]
Feb 20 20:27:56 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622476.7864] policy: auto-activating connection 'Auto Ethernet'
Feb 20 20:27:56 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622476.7888] device (lan1): Activation: starting connection 'Auto Ethernet' (dc33bf7c-5a51-4b1d-af8a-8c723a132b81)
Feb 20 20:27:56 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622476.7890] device (lan1): state change: disconnected -> prepare (reason 'none') [30 40 0]
Feb 20 20:27:56 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622476.7896] device (lan1): state change: prepare -> config (reason 'none') [40 50 0]
Feb 20 20:27:56 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622476.7899] device (lan1): state change: config -> ip-config (reason 'none') [50 70 0]
Feb 20 20:27:56 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622476.7901] dhcp4 (lan1): activation: beginning transaction (timeout in 45 seconds)
Feb 20 20:27:56 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622476.7925] dhcp4 (lan1): dhclient started with pid 7552
Feb 20 20:27:56 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622476.7990] device (lan1): link disconnected (deferring action for 4 seconds)
Feb 20 20:27:56 nico-lenovo-ubuntu dhclient[7552]: DHCPREQUEST of 192.168.0.21 on lan1 to 255.255.255.255 port 67 (xid=0x1e395bfb)
Feb 20 20:27:57 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622477.9499] device (lan1): link connected
Feb 20 20:27:59 nico-lenovo-ubuntu dhclient[7552]: DHCPREQUEST of 192.168.0.21 on lan1 to 255.255.255.255 port 67 (xid=0x1e395bfb)
Feb 20 20:28:00 nico-lenovo-ubuntu dhclient[7552]: DHCPACK of 192.168.0.21 from 192.168.0.1
Feb 20 20:28:00 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622480.4534] address 192.168.0.21
Feb 20 20:28:00 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622480.4534] plen 24 (255.255.255.0)
Feb 20 20:28:00 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622480.4535] gateway 192.168.0.1
Feb 20 20:28:00 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622480.4535] server identifier 192.168.0.1
Feb 20 20:28:00 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622480.4536] lease time 86400
Feb 20 20:28:00 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622480.4536] nameserver '194.168.4.100'
Feb 20 20:28:00 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622480.4537] nameserver '194.168.8.100'
Feb 20 20:28:00 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622480.4537] dhcp4 (lan1): state changed unknown -> bound
Feb 20 20:28:00 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622480.4643] device (lan1): state change: ip-config -> ip-check (reason 'none') [70 80 0]
Feb 20 20:28:00 nico-lenovo-ubuntu dhclient[7552]: bound to 192.168.0.21 -- renewal in 36449 seconds.
Feb 20 20:28:00 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622480.4670] device (lan1): state change: ip-check -> secondaries (reason 'none') [80 90 0]
Feb 20 20:28:00 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622480.4679] device (lan1): state change: secondaries -> activated (reason 'none') [90 100 0]
Feb 20 20:28:00 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622480.4760] manager: NetworkManager state is now CONNECTED_LOCAL
Feb 20 20:28:00 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622480.4761] manager: NetworkManager state is now CONNECTED_GLOBAL
Feb 20 20:28:00 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622480.4762] policy: set 'Auto Ethernet' (lan1) as default for IPv4 routing and DNS
Feb 20 20:28:00 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622480.4764] dns-mgr: Writing DNS information to /sbin/resolvconf
Feb 20 20:28:00 nico-lenovo-ubuntu dnsmasq[6728]: setting upstream servers from DBus
Feb 20 20:28:00 nico-lenovo-ubuntu dnsmasq[6728]: using nameserver 194.168.4.100#53(via lan1)
Feb 20 20:28:00 nico-lenovo-ubuntu dnsmasq[6728]: using nameserver 194.168.8.100#53(via lan1)
Feb 20 20:28:00 nico-lenovo-ubuntu dnsmasq[6728]: using nameserver 194.168.4.100#53(via wifi0)
Feb 20 20:28:00 nico-lenovo-ubuntu dnsmasq[6728]: using nameserver 194.168.8.100#53(via wifi0)
Feb 20 20:28:00 nico-lenovo-ubuntu NetworkManager[6715]: <info> [1487622480.4828] device (lan1): Activation: successful, device activated.

nico@nico-lenovo-ubuntu:~$ host google.com
;; connection timed out; no servers could be reached
nico@nico-lenovo-ubuntu:~$ host google.com
^Cnico@nico-lenovo-ubuntu:~$ host google.com 8.8.8.8
Using domain server:
Name: 8.8.8.8
Address: 8.8.8.8#53
Aliases:

google.com has address 216.58.198.238
google.com has IPv6 address 2a00:1450:4009:803::200e
google.com mail is handled by 10 aspmx.l.google.com.
google.com mail is handled by 30 alt2.aspmx.l.google.com.
google.com mail is handled by 20 alt1.aspmx.l.google.com.
google.com mail is handled by 40 alt3.aspmx.l.google.com.
google.com mail is handled by 50 alt4.aspmx.l.google.com.
nico@nico-lenovo-ubuntu:~$ ip route print
Command "print" is unknown, try "ip route help".
nico@nico-lenovo-ubuntu:~$ ip route
default via 192.168.0.1 dev lan1 proto static metric 100
default via 192.168.0.1 dev wifi0 proto static metric 600
169.254.0.0/16 dev lan1 scope link metric 1000
192.168.0.0/24 dev lan1 proto kernel scope link src 192.168.0.21 metric 100
192.168.0.0/24 dev wifi0 proto kernel scope link src 192.168.0.26 metric 600

nico@nico-lenovo-ubuntu:~$ route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.0.1 0.0.0.0 UG 100 0 0 lan1
0.0.0.0 192.168.0.1 0.0.0.0 UG 600 0 0 wifi0
169.254.0.0 0.0.0.0 255.255.0.0 U 1000 0 0 lan1
192.168.0.0 0.0.0.0 255.255.255.0 U 100 0 0 lan1
192.168.0.0 0.0.0.0 255.255.255.0 U 600 0 0 wifi0

nico@nico-lenovo-ubuntu:~$ sudo service network-manager restart
[sudo] password for nico:
nico@nico-lenovo-ubuntu:~$ host google.com
google.com has address 172.217.23.14
google.com has IPv6 address 2a00:1450:400b:802::200e
google.com mail is handled by 20 alt1.aspmx.l.google.com.
google.com mail is handled by 50 alt4.aspmx.l.google.com.
google.com mail is handled by 30 alt2.aspmx.l.google.com.
google.com mail is handled by 10 aspmx.l.google.com.
google.com mail is handled by 40 alt3.aspmx.l.google.com.

nico@nico-lenovo-ubuntu:~$ route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.0.1 0.0.0.0 UG 100 0 0 lan1
0.0.0.0 192.168.0.1 0.0.0.0 UG 600 0 0 wifi0
169.254.0.0 0.0.0.0 255.255.0.0 U 1000 0 0 lan1
192.168.0.0 0.0.0.0 255.255.255.0 U 100 0 0 lan1
192.168.0.0 0.0.0.0 255.255.255.0 U 600 0 0 wifi0

ProblemType: Bug
DistroRelease: Ubuntu 16.10
Package: network-manager 1.2.6-0ubuntu1
ProcVersionSignature: Ubuntu 4.8.0-38.41-lowlatency 4.8.17
Uname: Linux 4.8.0-38-lowlatency x86_64
ApportVersion: 2.20.3-0ubuntu8.2
Architecture: amd64
CurrentDesktop: XFCE
Date: Mon Feb 20 20:34:07 2017
IfupdownConfig:
 # interfaces(5) file used by ifup(8) and ifdown(8)
 auto lo
 iface lo inet loopback
InstallationDate: Installed on 2016-10-20 (122 days ago)
InstallationMedia: Ubuntu 16.10 "Yakkety Yak" - Release amd64 (20161012.2)
IpRoute:
 default via 192.168.0.1 dev lan1 proto static metric 100
 default via 192.168.0.1 dev wifi0 proto static metric 600
 169.254.0.0/16 dev lan1 scope link metric 1000
 192.168.0.0/24 dev lan1 proto kernel scope link src 192.168.0.21 metric 100
 192.168.0.0/24 dev wifi0 proto kernel scope link src 192.168.0.26 metric 600
NetworkManager.state:
 [main]
 NetworkingEnabled=true
 WirelessEnabled=true
 WWANEnabled=false
SourcePackage: network-manager
UpgradeStatus: No upgrade log present (probably fresh install)
nmcli-dev:
 DEVICE TYPE STATE DBUS-PATH CONNECTION CON-UUID CON-PATH
 lan1 ethernet connected /org/freedesktop/NetworkManager/Devices/0 lan1 2097e759-20cc-4bb4-bed4-ff0cf368c856 /org/freedesktop/NetworkManager/ActiveConnection/0
 wifi0 wifi connected /org/freedesktop/NetworkManager/Devices/1 Auto ITADINANTA ff29b784-80e3-4500-b9a5-dc057d7f91e1 /org/freedesktop/NetworkManager/ActiveConnection/1
 lan0 ethernet unavailable /org/freedesktop/NetworkManager/Devices/2 -- -- --
 lo loopback unmanaged /org/freedesktop/NetworkManager/Devices/3 -- -- --
nmcli-nm:
 RUNNING VERSION STATE STARTUP CONNECTIVITY NETWORKING WIFI-HW WIFI WWAN-HW WWAN
 running 1.2.6 connected started full enabled enabled enabled enabled disabled

[Nico Orrù (nigu-orru)]

If it helps, commenting out/removing

  # dns=dnsmasq

from

 /etc/NetworkManager/NetworkManager.conf

makes the problem go away.