VPLS (Virtual Private LAN Service)
A proposed IETF standard, VPLS is a class of VPN that supports the connection of multiple sites in a single bridged domain over a managed IP/Multi-protocol Label Switching (MPLS) network.
The goal is to overcome the limitations of ATM and frame relay for providing a protocol-transparent, any-to-any, full-mesh service across a WAN.
All services in a VPLS appear to be on the same LAN, regardless of location. This removes complexity from enterprise networks, and lets carriers scale the networks.
A VPLS presents an Ethernet interface to customers, simplifying the LAN/WAN boundary for service providers and customers, and enabling rapid and flexible service provisioning, because the service bandwidth is not tied to the physical interface. A 100M bit/sec interface can support a service-level agreement with anywhere from 1M to 100M bit/sec of customer traffic, typically in increments of 1M bit/sec.
A VPLS uses edge routers that can learn, bridge and replicate on a per-VPLS basis. These routers are connected by a full mesh of MPLS label switched path (LSP) tunnels, enabling any-to-any connectivity. Multiple services can be carried within each LSP tunnel.
All services in a VPLS are identified by a unique virtual channel label, which is exchanged between each pair of edge routers.
Edge routers use these virtual channel labels to demultiplex traffic arriving from different VPLS nodes over the same LSP tunnel. Label switch routers in the path switch traffic based on the outer (transport) label, so the virtual channel label is only visible to the final edge router, where the service terminates.
As traffic arrives on access ports, edge routers collect customers' media access control (MAC) addresses. Each router populates the addresses in a forwarding information base, or table of MAC addresses, it maintains for each VPLS node. All customer traffic is switched according to MAC addresses, and forwarded across the service provider network using the appropriate LSP tunnels.
Because most companies use routers for their WAN connections, the edge routers in a VPLS are exposed only to a single MAC address at each customer location, thus each edge router can scale to support thousands of VPLS services.
From VPLS removes complexity from networks, Network World Tech Update, 06/16/03.
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Virtual Private LAN Service
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