of participating PEs. Three implementations are being worked on: LDP The LDP method of PE auto-discovery is based on that used by the Label Distribution Protocol to distribute labels across P and PE routers within a single autonomous system. BGP The BGP method of PE auto-discovery is based on that used by Layer-3 MPLS VPNs to distribute VPN routes among PEs participating in a VPN. The BGP4 Multi-Protocol (BGP-MP) extensions are used to distribute VPN IDs and VPN-specific reachability information. Since IBGP requires either a full mesh of BGP sessions or the use of a route reflector, enabling the VPN ID in a participating PEs existing BGP configuration provides it with a list of all PEs in that VPN. Note that this method is for auto-discovery alone; LDP is still used for signaling. The method of establishing VPLS with BGP described above accomplishes both auto-discovery and signalling. RADIUS This method requires ALL PEs to be configured with one or more RADIUS servers to use. When the first CE router in a particular VPLS VPN connects to the PE, it uses the CE's identification to request authentication from the RADIUS server. This identification may be provided by the CE or may be configured into the PE for that particular CE. In addition to a username and password, the identification string also contains a VPN name and an optional provider name. The RADIUS server keeps track of all PEs that requested authentication for a particular VPN and returns a list of them to the PE requesting authentication. The PE then establishes LDP sessions to every PE in the list. See also Multiprotocol Label Switching (MPLS) Virtual leased line (VLL) IEEE 1355, which does something broadly similar via hardware. Virtual private network (VPN) Virtual LAN (VLAN) Virtual Extensible LAN (VXLAN) Virtual network Carrier Ethernet Ethernet VPN References External links "Virtual Private LAN Service (VPLS) Using BGP for Auto-Discovery and Signalling" Network protocols MPLS networking Virtual private networks