Re: virt-manager and networking

["Alexander V. Makartsev" <avbetev@gmail.com>]

On 06.06.2025 23:10, Charles Curley wrote:

> I'm setting up a new machine running trixie to run virtual machines,
> using virt-manager. virt-manager sets up a natted network for the
> virtual machines.
>
> Is it possible to set things up so that the virtual machines are on the
> same network as the host machine? The host is on 192.168.100.0/24. Can
> I have the virtual machines also on 192.168.100.0?
>
> Thank you.
>
>     
    Yes, you need to setup bridge interface on your host, think of it as
    virtual network switch and each VM and host would connect to its
    ports.
    Your host network config should look like this:
    $ sudo brctl show
      bridge name     bridge id               STP enabled     interfaces
      host-bridge             8000.fa04d78693ed       yes            
      VLAN20
                                                             
      srv-node1-vnet0
      ...
    
    $ sudo virsh net-dumpxml --network
      host-bridge
      <network>
        <name>host-bridge</name>
        <uuid>5b7b8ec5-ca1a-4066-8664-a2d107c9b083</uuid>
        <forward mode='bridge'/>
        <bridge name='host-bridge'/>
      </network>
    
    Network portion of VM config should look like this:
    $ sudo virsh dumpxml --domain srv-node1
      ...
      <interface type='bridge'>
            <mac address='52:54:00:34:55:2b'/>
            <source bridge='host-bridge'/>
            <target dev='srv-node1-vnet0'/>
            <model type='virtio'/>
            <alias name='net0'/>
            <address type='pci' domain='0x0000' bus='0x01'
      slot='0x00' function='0x0'/>
      </interface>
      ...
    
    <forward mode="bridge"/> part is essential. 
    The upside of this setup is that you will loose "double-NAT", which
    is default for libvirt\KVM, and prevent libvirt from modifying
    iptables ruleset.
    The downside is you'll have to provide DHCP service for VMs from
    external router and also make your host into a router to forward
    traffic from and to VMs.
    I wish I could provide a simple example from my system, but my
    configuration is more complicated, because I've split a single
    ethernet interface into multiple VLANs and use two bridges to
    completely isolate one VM from the host.
    It was easier for me to configure a complicated network setup like
    this with NetworkManager.
    
    The whole setup could be done by reading these articles:
    https://wiki.debian.org/BridgeNetworkConnections
https://wiki.libvirt.org/Networking.html#bridged-networking-aka-shared-physical-device

--

 With kindest regards, Alexander.

 Debian - The universal operating system
 https://www.debian.org