CentOS - Dec 2021 - Qemu - enabling "bridge mode" for primary physical interface for VMs

I have a physical host with a single physical network adapter. I want to host 
several VMs on host. (guest1 - guest4) The guest systems are accessible via 
192.168.122.* as is the default with qemu/virsh. 

There are 4 IP addresses being routed to the primary interface on host. I can 
set up an alias for the NIC and "see" these ip addresses. 

I understand that it's possible to allow the 4 VM guest systems to each have
a
"direct" fixed IP address and access the addresses \via the host
network
adapter, while the host retains its fixed IP. 

I've been googling like crazy and there is a lot of stale and conflicting 
information. 

Has anybody here done this successfully? 

Host and all guests are running CentOS 8.

Thanks.

Ben S
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The easiest way to set up bridged mode is to use virsh to convert the 
eth0 configuration to a new bridge, br0:

 ??? virsh iface-bridge eth0 br0 --no-stp

Once upon a time, Lists <lists at benjamindsmith.com>
said:
> I understand that it's possible to allow the 4 VM guest systems to each
have a
> "direct" fixed IP address and access the addresses \via the host
network
> adapter, while the host retains its fixed IP. 
If you are running NetworkManager (the default), it's not too hard.
Here's an example step-by-step for changing an existing interface
"em1" to
be a bridge "br0":


# Create a bridge interface
nmcli con add type bridge ifname br0 bridge.stp no

# Copy all the IPv4/IPv6 config from an existing interface
nmcli con mod bridge-br0 $(nmcli -f
ipv4.method,ipv4.addresses,ipv4.gateway,ipv6.method,ipv6.addresses,ipv6.gateway
con show em1 | grep -v -- -- | sed 's/:  */ /')
# -or- just set an IPv4 address/gateway to known values
nmcli con mod bridge-br0 ipv4.method manual ipv4.address 10.1.1.2/24
ipv4.gateway 10.1.1.1 ipv6.method ignore

# Make a connection for the physical ethernet em1 to be part of the bridge
nmcli con add type ethernet ifname em1 master bridge-br0

# Switch from the "regular" em1 to the bridge
nmcli con down em1; nmcli con up bridge-br0; nmcli con up bridge-slave-em1

# Disable the original config
nmcli con mod em1 autoconnect 0


Then you set your VMs to use the bridge - in the libvirt XML for
example, you'd have something like:

    <interface type='bridge'>
      <mac address='52:54:00:12:34:56'/>
      <source bridge='br0'/>
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00'
slot='0x03' function='0x0'/>
    </interface>


Inside the VM, configure the interface just as if it was a physical system
on that subnet.

-- 
Chris Adams <linux at cmadams.net>