openvswitch

Open vSwitch is a production quality, multilayer, software-based,
Ethernet virtual switch. It is designed to enable massive network
automation through programmatic extension, while still supporting
standard management interfaces and protocols (e.g. NetFlow, IPFIX,
sFlow, SPAN, RSPAN, CLI, LACP, 802.1ag). In addition, it is designed
to support distribution across multiple physical servers similar to
VMware's vNetwork distributed vswitch or Cisco's Nexus 1000V.