L2VPNs are provider-provisioned Layer 2 VPNs that extend the customer’s Layer 2 connectivity through an MPLS network. They do so by emulating different types of traditional data-link layer protocols, including Ethernet, Frame Relay, ATM, and others.
Like L3VPNs, L2VPNs depend entirely on the PE devices. Unlike L3VPNs, L2VPNs do not require that the PE devices participate in the customer’s routing algorithms. The latter statement means that a customer may run any type of Layer 3 protocol between sites, including IP.
An L2VPN may be implemented as a VPWS or a VPLS, where a VPWS provides point-to-point connectivity between two sites, and a VPLS provides point-to-multipoint connectivity between multiple sites. The control plane for either implementation may use LDP or BGP.
The L2VPN data plane is based on the pseudowire, which represents two virtual circuits between a pair of PE devices that are participating in an L2VPN. One virtual circuit is carried over an outgoing LSP, and the other is carried over an incoming LSP. Together, the two virtual circuits provide bidirectional communication for a customer.
