Open vSwitch is a production quality open source software switch designed to be used as a vswitch in virtualized server environments. A vswitch forwards traffic between different VMs on the same physical host and also forwards traffic between VMs and the physical network. OpenvSwitch supports standard management interfaces (e.g. sFlow, NetFlow, RSPAN, CLI), and is open to programmatic extension and control using OpenFlow and the OVSDB management protocol.
Open vSwitch as designed to be compatible with modern switching chipsets. This means that it can be ported to existing high-fanout switches allowing the same flexible control of the physical infrastructure as the virtual infrastructure. It also means that Open vSwitch will be able to take advantage of on-NIC switching chipsets as their functionality matures.
OpenVSwitch URL: http://openvswitch.org/