frequent network collapse possibly due to bridging

[Martin Kletzander]

On Fri, Jan 21, 2022 at 08:42:58AM -0600, Hakan E. Duran wrote:
>Hi,
>
>I would like some help to troubleshoot the problem I have been having
>lately with my VM host, which contains 5 VMs, one of which is for
>pi-hole, unbound services. It has been a relatively common occurrence in
>the last few weeks for me to find that the host machine has lost its
>network when I get back home from work. Restoring the VM/VMs do not fix
>the problem, the host needs to be restarted for a fix, otherwise there
>is both loss of name resolution, as well as an internet connection; I
>cannot ping even IPs such as 8.8.8.8. Since I use the pi-hole VM as the DNS
>server for my LAN, this means that my whole LAN gets disconnected from
>internet, until the host machine is rebooted. The host machine has a
>little complicated network setup: the two gigabit connections are bonded
>and bridged to the VMs; however this set up has been serving me so well
>for several years now. The problem, on the other hand, appeared a few
>weeks ago. This doesn't happen every day but often enough to be annoying
>and disruptive for my family.
>

Always good to check what has changed those weeks ago, but I understand
it is difficult to find out what you were updating and where.

>My question is, how can I troubleshoot this problem and figure out
>whether it is truly due to network bridging somehow collapsing or not? I
>tried to find some log files but all I could find were the
>/var/log/libvirt/qemu/$VM files, and the particular log file for the pi-hole
>VM reported the following lines; however, I am not sure if they are
>associated with a real crash or just due to shutting down and restarting
>the host (please excuse the word-wrapping):
>
>char device redirected to /dev/pts/2 (label charserial0)
>qxl_send_events: spice-server bug: guest stopped, ignoring
>2022-01-20T23:41:17.012445Z qemu-system-x86_64: terminating on signal 15 from pid 1 (/sbin/init)

Probably restarting the host as it got SIGTERM'd by init.  Maybe it was
restarted in a bad time and there is some inconsistency on the disk?
Using something like libvirt-guests which can manage your machines when
rebooting would be a good idea.

>2022-01-20 23:41:17.716+0000: shutting down, reason=crashed
>2022-01-20 23:42:46.059+0000: starting up libvirt version: 7.10.0, qemu
>version: 6.2.0, kernel: 5.10.89-1-MANJARO, hostname: -redacted-
>
>Please excuse my ignorance but is there a way to restart the
>networking without rebooting the host machine? This will not solve my

You can do:

virsh net-destroy <network_name>
virsh net-start <network_name>

but depending on what the network looks like, how it is set up etc. you
might need to restart some of the VMs or manually plug them in.

>problem since I won't be able to reach to the host remotely if the
>networking is down. The real solution would be preventing these network
>crashes and the first step in that would be effective troubleshooting in
>my opinion. Any input/guidance will be greatly appreciated.
>
>I can provide more info about my host/VM(s) if the above is not adequate.
>

I'm not sure how much more I can help as I do not understand what is the
actual setup.  What I would do is try to figure out what exactly happens
when it breaks and then go from that (setting up logging etc.), just
general tips I guess.

>Thanks,
>
>Hakan Duran
>


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