Fedora 22 libvirt with bridge

Fedora 22 comes with libvirt and NetworkManager and it is pre-configured with “default” NAT network. That’s fine, until you want to reach the NATed servers from your LAN. By the way this works in CentOS 7 too.

Good solution is network interface bridging. It was always a pain to configure this, but in Fedora 21 most of bugs were fixed and now it is possible to configure everything via NetworkManager.

In this tutorial, I will show you how to configure things without GUI. The commands below adds bridge in the system and reconfigures primary wired connection over that bridge. Make sure you set MAIN_CONN variable to the correct connection (use nmcli c show to find it).

I recommend to execute this in screen or tmux because connection will be lost during execution! Comment out IPv4 static configuration, if that’s your case.

yum -y install bridge-utils
yum -y groupinstall "Virtualization Tools"
export MAIN_CONN=enp8s0
bash -x <<EOS
systemctl stop libvirtd
nmcli c delete "$MAIN_CONN"
nmcli c delete "Wired connection 1"
nmcli c add type bridge ifname br0 autoconnect yes con-name br0 stp off
#nmcli c modify br0 ipv4.addresses ipv4.method manual
#nmcli c modify br0 ipv4.gateway
#nmcli c modify br0 ipv4.dns
nmcli c add type bridge-slave autoconnect yes con-name "$MAIN_CONN" ifname "$MAIN_CONN" master br0
systemctl restart NetworkManager
systemctl start libvirtd
systemctl enable libvirtd
echo "net.ipv4.ip_forward = 1" | sudo tee /etc/sysctl.d/99-ipforward.conf
sysctl -p /etc/sysctl.d/99-ipforward.conf

Do not, I repeat, do not execute this one by one. You need to do this in one “transaction” because connection will be lost and screen wont help you in this case. That’s why I use bash -x HEREDOC there.

Reboot might be needed if you encounter networking issues.

Now, when creating a VM in libvirt, make sure you select “br0” as the interface to use bridged networking. That’s all for today!

24 September 2015 | linux | fedora
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