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When I create a VM using virt-install, the VM gets connected to the virbr0 network interface automatically by generating this XML configuration:

<interface type="network">
  <source network="default"/>
  <mac address="52:54:00:6a:40:f8"/>
  <model type="e1000e"/>
</interface>

Now I'm trying to replicate that.

Checking the default libvirt network config at /var/lib/libvirt/dnsmasq/default.conf, I was able to tell the network interface name is virbr0.

I managed to tell qemu to use that same interface like this: qemu-system-x86_64 -net nic -net bridge,br=virbr0" ...

But I couldn't figure out how to specify a custom MAC address like it's done in the XML config. Could someone enlighten me?

For a tap device it seems you can set the MAC address like this

-netdev type=tap,id=net0,ifname=tap0,script=tap_ifup,downscript=tap_ifdown,vhost=on \
-device virtio-net-pci,netdev=net0,addr=19.0,mac=52:54:00:6a:40:f8

But that's not what I want. I just want to use that virbr0 bridge.

2
  • Yes, but the XML has nothing to do with qemu. It's just the libvirt XML generated by virt-install. I want to use qemu directly without the libvirt layer on top of it.
    – Forivin
    Aug 22 at 0:47
  • ok, i misunderstood
    – jsotola
    Aug 22 at 0:54
1

I finally figured it out!

So this is what virt-install will do by default:

sudo virt-install --network network=default,model=e1000,mac=00:11:22:33:44:55

And the equivalent with qemu-system-x86_64 would be:

INTERFACE_NAME="$(sudo cat /var/lib/libvirt/dnsmasq/default.conf | grep "^interface=" | cut -d'=' -f2-)"
sudo qemu-system-x86_64 -net nic,model=e1000,macaddr=00:11:22:33:44:55 -net bridge,br=${INTERFACE_NAME}

I would advise to make sure the default network is active first:

if ! sudo virsh net-list | grep default | grep --quiet active; then
    sudo virsh net-start default
fi

Note: The whole default network thing is provided by the package libvirt-daemon-config-network (at least on Fedora).

From the qemu man page:

   -net nic[,netdev=nd][,macaddr=mac][,model=type] [,name=name][,addr=addr][,vectors=v]
          Legacy  option to configure or create an on-board (or machine default) Network Interface Card(NIC) and connect it either to the emulated hub with ID 0 (i.e. the default hub), or to the netdev nd.  If model is omitted,
          then the default NIC model associated with the machine type is used. Note that the default NIC model may change in future QEMU releases, so it is highly recommended to always specify a model. Optionally, the  MAC  ad‐
          dress  can  be changed to mac, the device address set to addr (PCI cards only), and a name can be assigned for use in monitor commands. Optionally, for PCI cards, you can specify the number v of MSI-X vectors that the
          card should have; this option currently only affects virtio cards; set v = 0 to disable MSI-X. If no -net option is specified, a single NIC is created. QEMU can emulate several different models of network  card.   Use
          -net nic,model=help for a list of available devices for your target.

   -net user|tap|bridge|socket|l2tpv3|vde[,...][,name=name]
          Configure a host network backend (with the options corresponding to the same -netdev option) and connect it to the emulated hub 0 (the default hub). Use name to specify the name of the hub port.

From the virt-install man page:

NETWORKING OPTIONS
   -w, --network
       Syntax: -w, --network OPTIONS

       Connect the guest to the host network. Examples for specifying the network type:

       bridge=BRIDGE
              Connect to a bridge device in the host called BRIDGE. Use this option if the host has static networking config & the guest requires full outbound and inbound connectivity  to/from the LAN. Also use this if live migra‐
              tion will be used with this guest.

       network=NAME
              Connect  to  a virtual network in the host called NAME. Virtual networks can be listed, created, deleted using the virsh command line tool. In an unmodified install of libvirt there is usually a virtual network with a
              name of default. Use a virtual network if the host has dynamic networking (eg NetworkManager), or using wireless. The guest will be NATed to the LAN by whichever connection is active.

       type=direct,source=IFACE[,source.mode=MODE]
              Direct connect to host interface IFACE using macvtap.

       user   Connect to the LAN using SLIRP. Only use this if running a QEMU guest as an unprivileged user. This provides a very limited form of NAT.

       none   Tell virt-install not to add any default network interface.

       If --network is omitted a single NIC will be created in the guest. If there is a bridge device in the host with a physical interface attached, that will be used for connectivity. Failing that, the virtual network called  de‐
       fault will be used. This option can be specified multiple times to setup more than one NIC.

       Some example suboptions:

       model.type or model
              Network device model as seen by the guest. Value can be any nic model supported by the hypervisor, e.g.: 'e1000', 'rtl8139', 'virtio', ...

       mac.address or mac
              Fixed  MAC address for the guest; If this parameter is omitted, or the value RANDOM is specified a suitable address will be randomly generated. For Xen virtual machines it is required that the first 3 pairs in the MAC
              address be the sequence '00:16:3e', while for QEMU or KVM virtual machines it must be '52:54:00'.

       filterref.filter
              Controlling firewall and network filtering in libvirt. Value can be any nwfilter defined by the virsh 'nwfilter' subcommands. Available filters can be listed by running 'virsh  nwfilter-list',  e.g.:  'clean-traffic',
              'no-mac-spoofing', ...

       virtualport.* options
              Configure the device virtual port profile. This is used for 802.Qbg, 802.Qbh, midonet, and openvswitch config.

              Use --network=? to see a list of all available sub options.  Complete details at https://libvirt.org/formatdomain.html#elementsNICS

              This option deprecates -m/--mac, -b/--bridge, and --nonetworks

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