Understanding macvtap
This module works like a combination of the tap and macvlan modules. We already explained what the tap module does. The macvlan module enables us to create virtual networks that are pinned to a physical network interface (usually, we call this interface a lower interface or device). Combining tap and macvlan enables us to choose between four different modes of operation, called Virtual Ethernet Port Aggregator (VEPA), bridge, private, and passthru.
If we're using the VEPA mode (default mode), the physical switch has to support VEPA by supporting hairpin mode (also called reflective relay). When a lower device receives data from a VEPA mode macvlan, this traffic is always sent out to the upstream device, which means that traffic is always going through an external switch. The advantage of this mode is the fact that network traffic between virtual machines becomes visible on the external network, which can be useful for a variety of reasons. You can check...