Broadcast traffic and multicast traffic are flooded through a Virtual Private LAN Service(VPLS) network. VPLS is a Metro Ethernet (ME) technology that is used to implement Ethernet Multipoint Service (EMS) and Ethernet Relay Multipoint Service (ERMS) over a Multiprotocol Label Switching (MPLS) network. With VPLS, the service provider (SP) network emulates a single Layer 2 switch, or Ethernet bridge. Customer edge (CE) devices in a VPLS network connect directly to an SP-provided user provider edge (UPE) device, and the UPEs use virtual connections known as pseudowires (PWs) to interconnect through the SP network. The PWs form a fullmesh topology that creates a virtual switch instance (VSI), which emulates an 802.1 bridge.
The VPLS architecture creates a topology wherein each CE device can function as though it were a member of a virtual LAN (VLAN) on a physical switch. Because the SP network functions as a Layer 2 switch, broadcast and multicast packets received by the SP are always flooded through the network. Additionally, packets destined to unknown Media Access Control (MAC) addresses are initially flooded through the network until their MAC addresses and associated ports are correlated.