L2VPN

From the perspective of the IETF, a L2VPN is a VPN where traffic is forwarded based on the information provided in layer 2 protocol headers, for example, Ethernet, Frame Relay and ATM. If an IP packet exists within a layer 2 protocol, that IP packet would typically not be used by the layer 2 VPN to make decisions.

In the words of the IETF:

“There are two fundamentally different kinds of Layer 2 VPN service that a service provider could offer to a customer: Virtual Private Wire Service (VPWS) and Virtual Private LAN Service (VPLS).”

“A VPWS is a VPN service that supplies an L2 point-to-point service.”

“A VPLS is an L2 service that emulates LAN service across a Wide Area Network (WAN)”

Source: IETF RFC 4664

IETF has standardized a number of approaches to L2VPNs.

EVPN is currently the approach generating the most interest for future implementation.

In the words of the IETF:

“An EVPN instance comprises Customer Edge devices (CEs) that are connected to Provider Edge devices (PEs) that form the edge of the MPLS infrastructure. A CE may be a host, a router, or a switch. The PEs provide virtual Layer 2 bridged connectivity between the CEs. There may be multiple EVPN instances in the provider’s network.”

“In an EVPN, MAC learning between PEs occurs not in the data plane (as happens with traditional bridging in VPLS [RFC4761] [RFC4762]) but in the control plane. Control-plane learning offers greater control over the MAC learning process, such as restricting who learns what, and the ability to apply policies. Furthermore, the control plane chosen for advertising MAC reachability information is multi-protocol (MP) BGP (similar to IP VPNs [RFC4364]). This provides flexibility and the ability to preserve the “virtualization” or isolation of groups of interacting agents (hosts, servers, virtual machines) from each other. In EVPN, PEs advertise the MAC addresses learned from the CEs that are connected to them, along with an MPLS label, to other PEs in the control plane using Multiprotocol BGP (MP BGP). Control-plane learning enables load balancing of traffic to and from CEs that are multihomed to multiple PEs. This is in addition to load balancing across the MPLS core via multiple LSPs between the same pair of PEs. In other words, it allows CEs to connect to multiple active points of attachment. It also improves convergence times in the event of certain network failures.”

IETF RFC 7432