here are plenty of guides out there for making ethernet bridges in Linux to support virtual machines using built-in network scripts or NetworkManager. I decided to try my hand with creating a bridge using only systemd-networkd and it was surprisingly easy.
First off, you’ll need a version of systemd with networkd support. Fedora 20 and 21 will work just fine. RHEL/CentOS 7 and Arch Linux should also work. Much of the networkd support has been in systemd for quite a while, but if you’re looking for fancier network settings, like bonding, you’ll want at least systemd 216.