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).
