INTRODUCTION TO VPLS (VIRTUAL PRIVATE LAN SERVICE)

VPLS- It is a service that uses MPLS and Virtual Private Networking (VPN) to connect multiple LANs over the internet, thereby creating a logical LAN between geographically dispersed sites. It provides a secure and seamless connection. VPLS enables customers to maintain control of their own routing strategies. All customer routers in the VPLS service are part of the same subnet (LAN) which simplifies the IP addressing plan, especially when compared to a mesh constructed from many separate point-to-point connections.

So basically VPLS uses MPLS as a shared core network infrastructure enabling a service provider to extend a Layer 2 network across geographically separate/remote sites. It creates a virtual Ethernet switch at the provider’s edge to link remote sites.

VPLS is a mesh network topology which means each network device is connected to every other device through a dedicated link and there is no concept of a central hub, which acts as a central point of communication as figure-1 shows.

 

Figure-1

 

However, in VPLS, the service provider does not necessarily participate in the routing of customer sites. Thus the customer gets the option of doing routing on their own based on their needs.

How does VPLS work?

Consider Figure-1:

A packet originating within a service provider customer’s network is sent first to a customer edge-CE router /switch, which sends it to a provider edge-PE /router. Then the data is immediately sent to another router within the VPLS network using MPLS core infrastructure. The paths that carry VPLS network traffic are also called pseudo-wires. The pseudo-wires are signaled using either BGP or LDP as they provide a fast and direct connection similar to physical layer connections. Once the data packets arrive at the egress PE router, the traffic is forwarded to the CE device at the destination customer site.

Advantages of VPLS

  1. Routing Control- Service provider does not participate in the routing of customer routes.
  2. Level of Security- More secured since the provider does not participate in customer routing.
  3. Scalability- Less scalable than MPLS since Ethernet broadcast flooding consumes network bandwidth.
  4. Working Principle- VPLS uses the MAC address to locate the other endpoint

The difference between VPN  and VPLS is that VPLS, packets can traverse the service provider’s network in a point-to-multipoint fashion, meaning that a packet originating from a CE device can be broadcast to all the PE routers participating in a VPLS routing instance, while Layer 2 VPN forwards packets in point-to-point fashion only.

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