VPLS

VPLS, or Virtual Private LAN Service, is a multipoint-to-multipoint Layer 2 VPN technology that extends an Ethernet LAN over an MPLS backbone. It allows geographically dispersed customer sites to appear as a single Ethernet broadcast domain, enabling transparent bridging and MAC learning as if the sites were locally connected.

In typical deployments, customer edge devices connect to provider edge routers at each site. The provider backbone carries labeled packets between these PEs using pseudowires, forming a virtual Ethernet switch across the network. Control planes for establishing the service commonly rely on MP-BGP (multiprotocol BGP) or, in some cases, LDP to signal and create the pseudowires between PEs. MP-BGP-based VPLS can carry multiple VPNs and supports scalable discovery and topology management, while LDP-based approaches use label distribution to set up the required tunnels.

Traffic handling in VPLS is managed at the provider edge. Each PE learns MAC addresses from its local access LAN and forwards unknown destination frames to the appropriate remote PEs via pseudowires. Broadcast, unknown unicast, and multicast traffic is typically replicated at the PEs and sent to all other participating sites, which can introduce flooding across the VPN. VLAN-aware variants allow segmentation of traffic within the same VPLS instance, and some implementations support service features such as Ethernet OAM for fault management.

VPLS offers quick extension of LAN services across wide areas and simplifies the deployment of centralized network policies. However, it requires careful MAC address planning and traffic management to mitigate broadcast load and scalability challenges in large networks. It is commonly contrasted with VPWS (point-to-point) and VLL, which provide different degrees of multipoint connectivity. Standards and vendor implementations are largely aligned around the pseudowire and MP-BGP/VPLS concepts.