MPLS in the SDN Era

Chapter 7. Virtual Private LAN Service

Using a rough analogy, you can view a Virtual Private LAN Service (VPLS) instance like a Layer 2 (L2) VRF. Following are two important differences with respect to L3 VRFs:

• A real (L3) VRF provides virtualized routing, and VPLS provides virtualized switching.

• PEs advertise L3 (e.g., IP VPN) routes, but they do not advertise VPLS MAC routes to remote PEs.

VPLS just provides Multipoint-to-Multipoint (MP2MP) L2 connectivity between sites; MAC learning is performed in the forwarding plane—unlike IP routes, which are advertised in the control plane. It is very likely that in the following years Ethernet VPN (EVPN) takes over VPLS progressively, but as of this writing, the installed base of VPLS is big, so it deserves its own chapter.

Introduction to VPLS

VPLS is a virtual LAN switching instance with two types of interfaces: traditional Attachment Circuits (ACs) and Pseudowires (PWs). VPLS is a natural extension of Virtual Private Wire Service (VPWS). In a nutshell, here are differences:

• VPWS can support many L2 technologies; VPLS supports only Ethernet.

• VPWS is Point-to-Point (P2P), and VPLS is truly MP2MP. Actually, the topology can be quite arbitrary (full-mesh E-LAN, hub-and-spoke E-TREE, etc.) because both the usage of RTs in BGP VPLS and the manual definition of targeted neighbors in LDP VPLS provide that topological flexibility.

• VPWS does not perform MAC learning (it is not needed), and VPLS does it in the forwarding plane.