Layer 2 Vpn Architectures [Electronic resources] نسخه متنی

Chapter 15. Virtual Private LAN Service

Understanding VPLS fundamentals

VPLS deployment models

VPLS configuration case studies

The Layer 2 VPN architectures that have been discussed in this book so far share one common characteristic: They provide only point-to-point connectivity.

Virtual Private LAN Service (VPLS), on the other hand, is a Layer 2 VPN architecture that was built for multipoint connectivity and has broadcast capability.

Like other Layer 2 VPN architectures, customer edge (CE) routers are connected through provider edge (PE) routers and pseudowires, but they no longer have the point-to-point peering relationship. Instead, VPLS enables CE routers to communicate with one another as if they were attached to a common LAN.

Interestingly, pseudowires that are used in VPLS are the same type of pseudowire as that used in the point-to-point Layer 2 VPN architectures. The point-to-point versus multipoint behavior is determined by the data packet forwarding behaviors of a given Layer 2 VPN architecture. This also implies that the pseudowire encapsulation is orthogonal to the functionality that VPLS provides. In theory, both Multiprotocol Label Switching (MPLS) and L2TP pseudowires satisfy the forwarding requirements of VPLS. In reality, the rapid growth of MPLS network deployment drives the momentum behind the MPLS-based VPLS in terms of standardization activities and product implementations. Therefore, this chapter focuses on VPLS concepts and examples that involve MPLS pseudowires.

This chapter begins with an overview of VPLS that describes the service definitions, signaling protocols, and more importantly the concept of virtual switch and its data forwarding characteristics. Then it describes VPLS deployment issues of network topology, complexity, and scalability. VPLS configuration case studies conclude the chapter.