[CentOS] Qemu - enabling "bridge mode" for primary physical interface for VMs

Wed Dec 15 06:11:33 UTC 2021
Lists <lists at benjamindsmith.com>

Thank you, I'll be trying this on a spare machine here before I try it in 
production. Carefully reading the directions, although I see where bridge-br0 
is created, I don't see where bridge-slave-em1 is defined? 

On Tuesday, December 7, 2021 8:25:37 PM PST Chris Adams wrote:
> 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.gat
> eway 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
> ipv4.gateway 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.

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