libvirt QEMU/KVM guest cannot connect to network (NAT)

Question

An Ubuntu QEMU/KVM guest created in virt-manager with all default settings and network type NAT can't activate its network. My host is Fedora 35. A screenshot of the guest's NetworkManager log is below.

Here is the XML config from virt-manager's NIC tab in device settings:

<interface type="network">
  <mac address="redacted but present"/>
  <source network="default" portid="redacted but present" bridge="virbr0"/>
  <target dev="vnet2"/>
  <model type="virtio"/>
  <alias name="net0"/>
  <address type="pci" domain="0x0000" bus="0x01" slot="0x00" function="0x0"/>
</interface>

And virt-manager's virtual networks XML:

<network connections="2">
  <name>default</name>
  <uuid>redacted but present</uuid>
  <forward mode="nat">
    <nat>
      <port start="1024" end="65535"/>
    </nat>
  </forward>
  <bridge name="virbr0" stp="on" delay="0"/>
  <mac address="redacted but present"/>
  <ip address="192.168.122.1" netmask="255.255.255.0">
    <dhcp>
      <range start="192.168.122.2" end="192.168.122.254"/>
    </dhcp>
  </ip>
</network>

virsh net-list --all

 Name      State    Autostart   Persistent
--------------------------------------------
 default   active   yes         yes

brctl show

bridge name bridge id       STP enabled interfaces
virbr0      redacted    yes     

ip -br link show

lo               UNKNOWN        00:00:00:00:00:00 <LOOPBACK,UP,LOWER_UP>
enp34s0          UP             redacted <BROADCAST,MULTICAST,UP,LOWER_UP>
virbr0           DOWN           redacted <NO-CARRIER,BROADCAST,MULTICAST,UP>
wg-mullvad       UNKNOWN        <POINTOPOINT,UP,LOWER_UP>

nmcli connection show --active

NAME                UUID                                  TYPE       DEVICE
Wired connection 1  redacted  ethernet   enp34s0
virbr0              redacted  bridge     virbr0
wg-mullvad          redacted  wireguard  wg-mullvad

systemctl status libvirtd

○ libvirtd.service - Virtualization daemon
     Loaded: loaded (/usr/lib/systemd/system/libvirtd.service; disabled; vendor preset: disabled)
     Active: inactive (dead) since Mon 2022-04-04 05:13:01; 1min 40s ago
TriggeredBy: ○ libvirtd-tls.socket
             ● libvirtd-admin.socket
             ○ libvirtd-tcp.socket
             ● libvirtd.socket
             ● libvirtd-ro.socket
       Docs: man:libvirtd(8)
             https://libvirt.org
    Process: 36276 ExecStart=/usr/sbin/libvirtd $LIBVIRTD_ARGS (code=exited, status=0/SUCCESS)
   Main PID: 36276 (code=exited, status=0/SUCCESS)
        CPU: 439ms

Apr 04 05:12:49 host systemd[1]: Starting Virtualization daemon...
Apr 04 05:12:49 host systemd[1]: Started Virtualization daemon.
Apr 04 05:13:01 host systemd[1]: Stopping Virtualization daemon...
Apr 04 05:13:01 host systemd[1]: libvirtd.service: Deactivated successfully.
Apr 04 05:13:01 host systemd[1]: Stopped Virtualization daemon.
[user@host ~]$ sudo systemctl status libvirtd
○ libvirtd.service - Virtualization daemon
     Loaded: loaded (/usr/lib/systemd/system/libvirtd.service; disabled; vendor preset: disabled)
     Active: inactive (dead) since Mon 2022-04-04 05:13:01; 2min 1s ago
TriggeredBy: ○ libvirtd-tls.socket
             ● libvirtd-admin.socket
             ○ libvirtd-tcp.socket
             ● libvirtd.socket
             ● libvirtd-ro.socket
       Docs: man:libvirtd(8)
             https://libvirt.org
    Process: 36276 ExecStart=/usr/sbin/libvirtd $LIBVIRTD_ARGS (code=exited, status=0/SUCCESS)
   Main PID: 36276 (code=exited, status=0/SUCCESS)
        CPU: 439ms

Apr 04 05:12:49 host systemd[1]: Starting Virtualization daemon...
Apr 04 05:12:49 host systemd[1]: Started Virtualization daemon.
Apr 04 05:13:01 host systemd[1]: Stopping Virtualization daemon...
Apr 04 05:13:01 host systemd[1]: libvirtd.service: Deactivated successfully.
Apr 04 05:13:01 host systemd[1]: Stopped Virtualization daemon

systemctl --failed

  UNIT                  LOAD   ACTIVE SUB    DESCRIPTION
● nvidia-powerd.service loaded failed failed nvidia-powerd service

Things I've tried so far:

• Checked that I have the following packages installed: qemu dhclient netcat virt-viewer libvirt dnsmasq dmidecode ebtables virt-install virt-manager bridge-utils
• Checked that the network "default" is started in virsh
• Made sure that firewalld is installed and running
• Checked that virbr0 is in zone libvirt with firewall-cmd get-active-zones

CRUCIAL UPDATE:

Further troubleshooting showed that the VPN I am using is causing this issue. Launching VM's with the VPN disabled lets them connect to the network and internet. My VPN app is called Mullvad, and uses the Wireguard protocol. How can I make this work so that VM's connect to the internet through the VPN?

Answer 1

The problem was using a VPN without enabling an "allow local network sharing" setting. Enabling that made it work.

Answer 2

Enabling forwarding with

sysctl net.ipv4.ip_forward=1

might help.