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I'm new to virt-manager, qemu and libvirt so I barely know how to use them. I use virt-manager's GUI to make it easier for me to do a transition from VirtualBox (including VBoxManage) to KVM.

By far I know how to make my Virtual Machine with the GUI, but there's a huge problem: Once my VM is started - The network of the host and the guest is losing connection.

No matter if it's NAT or Bridge, Once the VM is started - No network for the Host, nor the Guest. I can't browse the web to find a solution as long as the VM is running - I must shut it off and then the network is restored.

I went to journalctl -r (with sudo) to see what can cause it. I'm not that good at understanding the output of journalctl, so I'm sharing it here, and maybe someone can find the problem within my logs?

Apr 20 19:01:41 myuser systemd[1]: NetworkManager-dispatcher.service: Deactivated successfully.
Apr 20 19:01:32 myuser kernel: audit: type=1400 audit(1713628892.242:110): apparmor="STATUS" operation="profile_remove" profile="unconfined" name="libvirt-92b7cf2e-326>
Apr 20 19:01:32 myuser audit[59392]: AVC apparmor="STATUS" operation="profile_remove" profile="unconfined" name="libvirt-92b7cf2e-3262-4f04-ad63-37d5e4d94b70" pid=5939>
Apr 20 19:01:32 myuser connmand[1102]: virbr1 {newlink} index 7 operstate 2 <DOWN>
Apr 20 19:01:32 myuser connmand[1102]: virbr1 {newlink} index 7 address 52:54:00:6B:A6:9E mtu 1500
Apr 20 19:01:32 myuser connmand[1102]: virbr1 {update} flags 4099 <UP>
Apr 20 19:01:32 myuser connmand[1102]: virbr1 {TX} 28 packets 3938 bytes
Apr 20 19:01:32 myuser connmand[1102]: virbr1 {RX} 40 packets 3476 bytes
Apr 20 19:01:32 myuser connmand[1102]: vnet2 {dellink} index 8 operstate 2 <DOWN>
Apr 20 19:01:32 myuser connmand[1102]: virbr1 {newlink} index 7 operstate 6 <UP>
Apr 20 19:01:32 myuser connmand[1102]: virbr1 {newlink} index 7 address 52:54:00:6B:A6:9E mtu 1500
Apr 20 19:01:32 myuser connmand[1102]: virbr1 {update} flags 4163 <UP,RUNNING>
Apr 20 19:01:32 myuser connmand[1102]: virbr1 {TX} 28 packets 3938 bytes
Apr 20 19:01:32 myuser connmand[1102]: virbr1 {RX} 40 packets 3476 bytes
Apr 20 19:01:32 myuser connmand[1102]: Remove interface (null) [ ethernet ]
Apr 20 19:01:32 myuser connmand[1102]: (null) {remove} index 8
Apr 20 19:01:32 myuser connmand[1102]: vnet2 {dellink} index 8 operstate 2 <DOWN>
Apr 20 19:01:32 myuser connmand[1102]: vnet2 {newlink} index 8 operstate 2 <DOWN>
Apr 20 19:01:32 myuser connmand[1102]: vnet2 {newlink} index 8 address FE:54:00:DB:3A:50 mtu 1500
Apr 20 19:01:32 myuser connmand[1102]: (null) {del} address 169.254.64.167/16 label vnet2
Apr 20 19:01:32 myuser connmand[1102]: vnet2 {newlink} index 8 operstate 2 <DOWN>
Apr 20 19:01:32 myuser connmand[1102]: vnet2 {newlink} index 8 address FE:54:00:DB:3A:50 mtu 1500
Apr 20 19:01:32 myuser connmand[1102]: (null) {del} route fe80:: gw :: scope 0 <UNIVERSE>
Apr 20 19:01:32 myuser connmand[1102]: Removing default interface route failed (No such device)
Apr 20 19:01:32 myuser connmand[1102]: Removing default interface route failed (No such device)
Apr 20 19:01:32 myuser connmand[1102]: vnet2 {newlink} index 8 operstate 2 <DOWN>
Apr 20 19:01:32 myuser connmand[1102]: vnet2 {newlink} index 8 address FE:54:00:DB:3A:50 mtu 1500
Apr 20 19:01:32 myuser systemd-machined[935]: Machine qemu-3-linux2022 terminated.
Apr 20 19:01:32 myuser systemd[1]: machine-qemu\x2d3\x2dlinux2022.scope: Consumed 22.066s CPU time.
Apr 20 19:01:32 myuser systemd[1]: machine-qemu\x2d3\x2dlinux2022.scope: Deactivated successfully.
Apr 20 19:01:31 myuser systemd[1]: Started NetworkManager-dispatcher.service - Network Manager Script Dispatcher Service.
Apr 20 19:01:31 myuser dbus-daemon[928]: [system] Successfully activated service 'org.freedesktop.nm_dispatcher'
Apr 20 19:01:31 myuser systemd[1]: Starting NetworkManager-dispatcher.service - Network Manager Script Dispatcher Service...
Apr 20 19:01:31 myuser dbus-daemon[928]: [system] Activating via systemd: service name='org.freedesktop.nm_dispatcher' unit='dbus-org.freedesktop.nm-dispatcher.service>
Apr 20 19:01:31 myuser NetworkManager[1101]: <info>  [1713628891.9478] device (vnet2): released from master device virbr1
Apr 20 19:01:31 myuser NetworkManager[1101]: <info>  [1713628891.9474] device (vnet2): state change: activated -> unmanaged (reason 'unmanaged', sys-iface-state: 'remo>
Apr 20 19:01:31 myuser avahi-daemon[925]: Withdrawing address record for 169.254.64.167 on vnet2.
Apr 20 19:01:31 myuser avahi-daemon[925]: Withdrawing address record for fe80::fc54:ff:fedb:3a50 on vnet2.
Apr 20 19:01:31 myuser avahi-daemon[925]: Leaving mDNS multicast group on interface vnet2.IPv4 with address ***.***.**.***.
Apr 20 19:01:31 myuser avahi-daemon[925]: Interface vnet2.IPv4 no longer relevant for mDNS.
Apr 20 19:01:31 myuser connman-vpnd[927]: virbr1 {newlink} index 7 operstate 2 <DOWN>
Apr 20 19:01:31 myuser connman-vpnd[927]: virbr1 {newlink} index 7 address 52:54:00:6B:A6:9E mtu 1500
Apr 20 19:01:31 myuser connman-vpnd[927]: virbr1 {update} flags 4099 <UP>
Apr 20 19:01:31 myuser connman-vpnd[927]: vnet2 {dellink} index 8 operstate 2 <DOWN>
Apr 20 19:01:31 myuser connman-vpnd[927]: virbr1 {newlink} index 7 operstate 6 <UP>
Apr 20 19:01:31 myuser connman-vpnd[927]: virbr1 {newlink} index 7 address 52:54:00:6B:A6:9E mtu 1500
Apr 20 19:01:31 myuser connman-vpnd[927]: virbr1 {update} flags 4163 <UP,RUNNING>
Apr 20 19:01:31 myuser kernel: virbr1: port 1(vnet2) entered disabled state
Apr 20 19:01:31 myuser kernel: device vnet2 left promiscuous mode
Apr 20 19:01:31 myuser connman-vpnd[927]: vnet2 {remove} index 8
Apr 20 19:01:31 myuser connman-vpnd[927]: vnet2 {dellink} index 8 operstate 2 <DOWN>
Apr 20 19:01:31 myuser connman-vpnd[927]: vnet2 {newlink} index 8 operstate 2 <DOWN>
Apr 20 19:01:31 myuser connman-vpnd[927]: vnet2 {newlink} index 8 address FE:54:00:DB:3A:50 mtu 1500
Apr 20 19:01:31 myuser connman-vpnd[927]: vnet2 {newlink} index 8 operstate 2 <DOWN>
Apr 20 19:01:31 myuser kernel: virbr1: port 1(vnet2) entered disabled state
Apr 20 19:01:31 myuser connman-vpnd[927]: vnet2 {newlink} index 8 address FE:54:00:DB:3A:50 mtu 1500

I have enabled libvirt in firewalld's zones: home, trusted and even public. It doesn't seem to work.

Using Debian 12.5 (Bookworm), LXQt Desktop GUI

Update: When I set the network of the VM to "Isolate", I might not have any network on my VM, but the network on my host will work. It happens on non-isolate networks

Update 2: I stopped firewalld and that didn't helped, so it's not a firewall problem

Please help me to solve this problem. Thank you

Response for @A B -

Updated - When the VM is ON (Host)*:

$ sudo bash -c "ip link; ip -br addr; ip route; ip rule; ip neigh"
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 10:7b:44:93:7e:60 brd ff:ff:ff:ff:ff:ff
3: enx00e04c6802a7: <NO-CARRIER,BROADCAST,MULTICAST,DYNAMIC,UP> mtu 1500 qdisc fq_codel state DOWN mode DEFAULT group default qlen 1000
    link/ether 00:e0:4c:68:02:a7 brd ff:ff:ff:ff:ff:ff
5: virbr0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
    link/ether 52:54:00:3a:4a:9b brd ff:ff:ff:ff:ff:ff
6: vnet0: <BROADCAST,MULTICAST,DYNAMIC,UP,LOWER_UP> mtu 1500 qdisc noqueue master virbr0 state UNKNOWN mode DEFAULT group default qlen 1000
    link/ether fe:54:00:d6:4a:49 brd ff:ff:ff:ff:ff:ff
lo               UNKNOWN        127.0.0.1/8 ::1/128 
enp3s0           UP             192.168.1.9/24 fe80::127b:44ff:fe93:7e60/64 
enx00e04c6802a7  DOWN           
virbr0           UP             192.168.100.1/24 
vnet0            UNKNOWN        169.254.149.177/16 fe80::fc54:ff:fed6:4a49/64 
0.0.0.0 dev vnet0 scope link 
default dev vnet0 scope link 
169.254.0.0/16 dev vnet0 proto kernel scope link src 169.254.149.177 
192.168.1.0/24 dev enp3s0 proto kernel scope link src 192.168.1.9 
192.168.1.1 dev enp3s0 scope link 
192.168.100.0/24 dev virbr0 proto kernel scope link src 192.168.100.1 
0:      from all lookup local
32766:  from all lookup main
32767:  from all lookup default
192.168.1.6 dev enp3s0 lladdr 00:00:c0:34:14:db STALE 
192.168.100.202 dev virbr0 lladdr 52:54:00:d6:4a:49 STALE 
192.168.1.1 dev enp3s0 lladdr 74:da:88:d6:c8:e6 STALE 
198.252.206.25 dev vnet0 FAILED 
192.168.1.5 dev enp3s0 lladdr 50:eb:f6:24:85:a6 STALE 
fe80::76da:88ff:fed6:c8e6 dev enp3s0 lladdr 74:da:88:d6:c8:e6 router STALE 
fe80::9c7a:f1bb:ca7f:4c1e dev enp3s0 lladdr 50:eb:f6:24:85:a6 STALE 
$ sudo systemctl stop firewalld.service && sudo nft list ruleset
table ip filter {
}
table ip nat {
}
table ip mangle {
}
table ip6 filter {
}
table ip6 nat {
}
table ip6 mangle {
}
$ sudo cat /etc/resolv.conf
# Generated by resolvconf
nameserver 192.168.1.1
  • As I said - I don't have a terminal (or I don't know how to access it) while I'm installing debian on the guest, so I can't provide the information from the guest
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9
  • Maybe there's a resource that should be unique that isn't unique anymore? Could you give twice, in both the host and the VM, the output of ip link; ip -br addr; ip route; ip rule; ip neigh and also on the host (with the firewall deactivated) nft list ruleset. While at it also twice the content of /etc/resolv.conf. Commented Apr 20, 2024 at 18:43
  • @A.B Thank you for helping and answering - I've updated my question with a response ^ Commented Apr 20, 2024 at 19:06
  • It has to be run when the network problem happens: when VM is running (even if being installed), or it won't help . Try again when the problem is happening: loss of network (even try to navigate a bit) and rerun these commands on the host while network doesn't work, stop the VM (to get network back) and put back their result in the question. Commented Apr 20, 2024 at 19:09
  • @A.B Hi, Thank you again. I have updated my response Commented Apr 20, 2024 at 19:16
  • I can only confirm there's a wrong setting somewhere, triggering default dev vnet0 scope link : default route towards the VM's NIC instead of Internet. There has to be a setting that has been set wrong somewhere, but I can't guess what. Commented Apr 20, 2024 at 19:24

2 Answers 2

Reset to default
1

With the help of @A.B, I figured out what was the problem - And... HOW TO SOLVE IT!

A.B gave me a hint about using both connmand and NM (NetworkManager). I started to investigate the problem, and I've found out that Virt-manager is using NM for the networking, while my device/interface (enp3s0) is controlled through connmand (which is part of LXQt's GUI).

So I did the following:

  1. I've decided to enable my device using NetworkManager. NM said that my device is "Strictly unmanaged", So I decided to free my device from connman. It was complicated. I ran the find command over every connman's possible directory (in /var/lib and /etc), and found nothing related to my device.
  2. I decided to look for NM's directories - Maybe it's configured there? When I found out that nope:
  3. I've decided to stop and disable connmand for a while. But yet, Virt-manager still wasn't able to use this device.
  4. So I went to extreme - I've purged connman*, forever, and moved to NM.
  5. Still didn't worked, but it was for good - because once i've commented the device from the /etc/network/interfaces file, NM took control over it (with the help of sudo nmcli device set enp3s0 managed true), and I finally got it working through NM.
  6. A reboot (because i'm used to it since Windows, though I didn't had to), and now I have network in both client AND host!
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As you figured yourself, it's ConnMan. It seems to be incompatible with libvirt. ConnMan is installed by default in Devuan, which I use. When I uninstalled ConnMan and installed NetworkManager, the problem went away immediately. Then I uninstalled NetworkManager too, and left the built-in, basic ifupdown and /etc/network/interfaces file. It still works. Something in ConnMan causes libvirt to go haywire and spawn all these vnet networks. It's not happening when ifupdown or NetworkManager manages it.

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