I'm running Ubuntu 16.04 on my server which is used for virtualization. It's running multiple Ubuntu 16.04 guest using the qemu-kvm software for virtualization. The server is using libvirt to manage the guest (autostart, start/stop etc.) and I have all of the guest set-up to autostart on host boot.
When the host is booting everything seems normal without any errors and the internet is working as it should. But when I open a VNC connection to any of the hosts while it's still booting I can see that the networking fails (Failed to start Raise network interfaces.). This only happens on a cold boot. By that I mean it only happens when I boot the server and the guest gets automatically booted after the host is online. When this happens, I can simply restart the host manually and it will work fine without any problems. I can also just restart the particular interfaces (ifdown -f eth0 && ifup eth0) to make the internet work again.
Most guests have only one interface (eth0) and is requesting a static IPv4 and a static IPv6 address from the router. One thing I've noticed is that the IPv6 route has the "expire x seconds" option on it, while the IPv4 does not. This causes the guest to not be accessible over IPv6 when the route expires. Is this expire there because of the Raise network interfaces failing on boot?
I'm trying to find out why the guests are all having problem getting the interface working on a cold boot. It's very annoying having to (re)start all guests manually. The hosts' syslog does not show any errors related to the networking service, and the guests only have this error: "RTNETLINK answers: File exists" without any further errors.