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I have a home server setup where Ubuntu 16.04 hosts a couple of Ubuntu server virtual machines. Everything ran smoothly for half a year until this week I installed the updates to the physical machine and after that the virtual machines lost their connection to internet.

Here are some details:

  • I'm using Virtual Machine Manager to manage the VMs
  • VMs are KVM
  • The physical host is behind a NAT and the network should bridged to VMs
  • VMs have static IP addresses
  • I am seeing their IP and MAC addresses on my router's active client list
  • I'm able to login via SSH to the VMs, but once in the VM is not able to ping anything (FQDNs nor direct IPs) nor reach apt repositories

Here is the content of a VM's /etc/network/interfaces:

$ cat /etc/network/interfaces
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto ens3
iface ens3 inet static
address 192.168.0.6
netmask 255.255.255.0
network 192.168.0.0
broadcast 192.168.0.255
gateway 192.168.0.1
dns-nameservers 192.168.0.1 8.8.8.8 8.8.4.4

VM's ifconfig:

$ ifconfig

ens3      Link encap:Ethernet  HWaddr 52:54:00:5c:7c:8b
          inet addr:192.168.0.6  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::5054:ff:fe5c:7c8b/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2855 errors:0 dropped:0 overruns:0 frame:0
          TX packets:9564 errors:0 dropped:0 overruns:0 carrier:0
          collisions:54129 txqueuelen:1000
          RX bytes:148974 (148.9 KB)  TX bytes:791122 (791.1 KB)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:22025 errors:0 dropped:0 overruns:0 frame:0
          TX packets:22025 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1
          RX bytes:2270863 (2.2 MB)  TX bytes:2270863 (2.2 MB)

Some connectivity tests I ran:

$ sudo apt update
Err:1 http://fi.archive.ubuntu.com/ubuntu xenial InRelease
  Temporary failure resolving 'fi.archive.ubuntu.com'
Err:2 http://security.ubuntu.com/ubuntu xenial-security InRelease
  Temporary failure resolving 'security.ubuntu.com'
Err:3 http://fi.archive.ubuntu.com/ubuntu xenial-updates InRelease
  Temporary failure resolving 'fi.archive.ubuntu.com'
0% [Working]^C

-

$ ping -v google.fi
^C

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$ ping 172.217.18.3
PING 172.217.18.3 (172.217.18.3) 56(84) bytes of data.
^C
--- 172.217.18.3 ping statistics ---
26 packets transmitted, 0 received, 100% packet loss, time 25198ms

Any idea what more could I check to resolve this issue?

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After further investigation I came to the conclusion that there must be something wrong with my bridge adapter. I ended up setting my bridge and network settings on the hypervisor from scratch and after a reboot all virtual machines were fully functioning again.

I have a hunch that a relatively fresh docker setup somehow conflicted with the parallel virtual infrastructure, but I failed to find the actual problem in the configuration so I cannot be 100% sure.

Anyway, this time the solution was a fresh build of a bridge configuration.

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