On 10/25/22 17:03, Armin Lepir wrote:
> Hi 
>
> I am using libvrt for the first time. Im building a KVM for multiple
> Virtual OS instances.
>
> The problem i have is with your official documentation for Virtual
> Networking.
>
> https://wiki.libvirt.org/page/VirtualNetworking
> <https://wiki.libvirt.org/page/VirtualNetworking>
>

Please note that our wiki page is obsolete and we tried to move
everything into our knowledge base articles:

  https://libvirt.org/kbase/

We're keeping the wiki around though, because maybe not everything was
moved.

>
> The following is wrong:
>
> The default mode is BRIDGE + NAT.
>
> Optional mode is ROUTING.
>
>
> It should be:
>
> The default mode is ROUTING + NAT.
>
> Optional mode is BRIDGE.
>
>
> As far as i know a bridge operates on the Layer2.
>
> IP and NAT operate on the Layer3.
>
> NAT can not operate on the L2.
>
> Please tell me that im wrong and explain how am i wrong.

If we'd be talking about bare metal network components then you are 100%
correct. Except, the Linux bridge is more than just plain L2 bridge. It
can have an IP address, route traffic, serve as network interface (when
a host is sending a packet to a guest, the packet is injected into said
bridge).

What the wiki page is trying to say, that by default you'll get this
'default' network which uses this Linux 'bridge' + NAT. Optionally, you
can define new network, or modify the existing one to switch to so
called routed mode.

Hope this clears things up.

Michal