VPLS: Extending LANs Across WANs

Author Ermias Teffera

At ITVue Networks, we specialize in high-performance WAN solutions that allow enterprises to connect multiple sites seamlessly. After exploring Fiber, SDH/SONET, and Metro Ethernet, it’s time to dive into VPLS (Virtual Private LAN Service) — a technology that extends Layer 2 LAN services across a wide-area network.

What is VPLS?

VPLS is a Layer 2 VPN technology that allows multiple geographically dispersed sites to appear as if they are on the same LAN. It uses MPLS (Multiprotocol Label Switching) or IP-based transport to provide transparent LAN connectivity over a provider network.

Key Benefits:

• LAN-like experience: Sites can communicate over a WAN as if they are on the same local network

• Transparency: Supports VLANs, multicast, and broadcast traffic

• Scalability: Connect multiple branches to a central VPLS domain

• Simplicity: Reduces the need for complex routing between sites

VPLS Architecture

A typical VPLS architecture uses provider edge (PE) routers to connect customer sites:

• Each customer site connects to a PE router.

• PE routers forward traffic over the provider network to other PE routers in the same VPLS domain.

• The WAN appears as a single broadcast domain to the customer.

Types of VPLS Services

1. Full-Mesh VPLS

   • Every site is connected to every other site via the provider network.

   • Advantage: True LAN connectivity, all-to-all communication

   • Disadvantage: Requires more resources as the number of sites grows

     
     

2. Hub-and-Spoke VPLS

   
   

   • A central site (hub) connects to all other sites (spokes)

   • Advantage: Scales better than full-mesh

   • Disadvantage: Traffic between spokes must pass through the hub

Key Components

• Customer Edge (CE) Router: Connects the customer site to the provider network

• Provider Edge (PE) Router: Terminates VPLS connections and forwards Layer 2 traffic across the provider network

• Provider Core (P) Router: Provides backbone forwarding, often MPLS-based

  
  

VPLS Over MPLS

Most VPLS implementations use MPLS in the provider backbone:

• Labels: MPLS labels forward Ethernet frames between PE routers

• Encapsulation: Customer VLANs are encapsulated in MPLS frames

• Loop Prevention: VPLS uses split-horizon rules to prevent loops within the LAN-like domain

Cisco Configuration Example

• l2vpn vfi context defines the VPLS instance

• autodiscovery bgp enables automatic neighbor discovery in MPLS-based VPLS

• neighbor specifies remote PE router participating in the VPLS

Real-World Applications

• Retail chains: Connect multiple stores to a central data center as if on the same LAN

• Financial institutions: Low-latency Layer 2 connectivity for trading applications

• Enterprise campuses: Branch offices share VLANs and multicast traffic transparently

  
  

Best Practices

• Use hub-and-spoke VPLS for large deployments to reduce PE router load

• Monitor MAC table size on PE routers to prevent flooding issues

• Combine with QoS policies to prioritize voice and video traffic

• Deploy redundant PE routers and WAN paths for high availability

Conclusion

VPLS provides a transparent, scalable, and LAN-like experience across WANs, making it ideal for enterprises that need Layer 2 connectivity between multiple sites. At ITVue Networks, we implement VPLS to enable seamless, high-performance connectivity for clients, supporting modern applications and workloads.