libvirt users - Aug 2022 - libvirt can't setup simple bridged network?

I feel like I'm taking crazy pills!  I'm reading the libvirt network XML
format documentation[1], and I can't figure out how to create a simple
bridged network - no NAT, no routing, no OVS, no  macvtap, etc.  I.e.,
just a Linux bridge with a single physical interface attached.

None of the 3 scenarios listed for <forward mode='bridge'>
describe the
simple setup that I'm trying to create, so it looks like I'll need to
create the bridge separately.  (It's not hard to do, it just seems like
such a weird gap the in the functionality.)


[1] https://libvirt.org/formatnetwork.html

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=======================================================================Google   
Where SkyNet meets Idiocracy
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Not to tangent (top post), but ...

This is where I leverage NetworkManager in general (and have a set of
standard nmcli commands and Ansible tooling for common scenarios) ...
_avoiding_ libvirtd altogether.  I'm even debating about taking away the
default 192.168.122/24 NAT subnet as standard in new builds with QEMU/KVM
installed, just because of past issues with pre/post routing, or even IP
address range conflicts (long story).  It's easy to overlook those as well.

YMMV, including with oVirt.

On Mon, Aug 15, 2022 at 10:17 AM Ian Pilcher <arequipeno at gmail.com>
wrote:
> I feel like I'm taking crazy pills!  I'm reading the libvirt
network XML
> format documentation[1], and I can't figure out how to create a simple
> bridged network - no NAT, no routing, no OVS, no  macvtap, etc.  I.e.,
> just a Linux bridge with a single physical interface attached.
>
> None of the 3 scenarios listed for <forward mode='bridge'>
describe the
> simple setup that I'm trying to create, so it looks like I'll need
to
> create the bridge separately.  (It's not hard to do, it just seems like
> such a weird gap the in the functionality.)
>
> [1] https://libvirt.org/formatnetwork.html

-- 
Bryan J Smith  -  http://www.linkedin.com/in/bjsmith
E-mail:  b.j.smith at ieee.org  or  me at bjsmith.me
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On 8/15/22 10:11 AM, Ian Pilcher wrote:
> I feel like I'm taking crazy pills!? I'm reading the libvirt
network XML
> format documentation[1], and I can't figure out how to create a simple
> bridged network - no NAT, no routing, no OVS, no? macvtap, etc.? I.e.,
> just a Linux bridge with a single physical interface attached.
> 
> None of the 3 scenarios listed for <forward mode='bridge'>
describe the
> simple setup that I'm trying to create, so it looks like I'll need
to
> create the bridge separately.? (It's not hard to do, it just seems like
> such a weird gap the in the functionality.)
> 
> 
> [1] https://libvirt.org/formatnetwork.html
> 
libvirt's virtual network driver historically only creates networks that 
don't touch (and potentially mess up) the existing host system network 
config. But attaching a physical host system ethernet to a bridge 
requires moving the ethernet device's IP config over to the bridge, so 
that was considered "out of scope" for libvirt's network driver.

Back in 2008-2009, libvirt added an "interface driver" whose purpose
was
to configure/reconfigure host system network interfaces to, for example, 
attach a host ethernet to a bridge device, or add a vlan interface based 
on a host ethernet (and then attach that vlan interface to a bridge). 
This was initially supported on Fedora/CentOS/RHEL platforms using a (at 
the time new) library called netcf. After several years of floundering, 
I proposed in 2020 that we essentially admit failure and deprecate the 
netcf library (and libvirt's use of it). I don't have the energy to 
rehash the entire list of reasons here, but my message proposing the 
deprecation and listing all the reasons, is here:

https://listman.redhat.com/archives/libvir-list/2020-December/212781.html

These days (and even before, for the most part) if you want a bridge 
attached to a host system ethernet, it's recommended that you set that 
up using whatever host system network config you're using (e.g., 
NetworkManager, systemd-networkd, ifcfg files, /etc/network/interfaces 
file), and then either define your guest interfaces with <interface 
type='bridge'>, or if you want to use <interface
type='network'>
andrefer to that with a libvirt network name, create a libvirt network 
with <forward mode='bridge'> (which expects that a bridge device
will
have already been created in the host system network config).