Multiprotocol Label Switching

"MPLS" redirects here. For the U.S. city, see Minneapolis. For other uses, see MPLS (disambiguation).

Multiprotocol Label Switching (MPLS) is a routing technique in telecommunications networks that directs data from one node to the next based on labels rather than network addresses. Whereas network addresses identify endpoints, MPLS labels identify established paths between endpoints. MPLS can encapsulate packets of various network protocols and supports a range of access technologies, including T1/E1, ATM, Frame Relay, and DSL.

MPLS was originally developed to improve packet forwarding by reducing the reliance on complex routing table lookups. With the introduction of hardware-based forwarding engines, forwarding speed is no longer the main reason for deployment, and MPLS today is more often used for traffic engineering, differentiated services quality of service, and BGP/MPLS IP virtual private networks (VPNs).

In an MPLS network, packet-forwarding decisions are made solely on the contents of labels, without the need to examine the packet itself. This allows for the creation of end-to-end connections across any type of transport medium, using any protocol. The primary benefit is to eliminate dependence on a particular OSI data link layer technology, and eliminate the need for multiple layer-2 networks to satisfy different types of traffic. Multiprotocol label switching belongs to the family of packet-switched networks.

MPLS operates at a layer between traditional definitions of OSI Layer 2 (data link layer) and Layer 3 (network layer), and is often referred to as a layer 2.5 protocol. It was designed to provide a unified data-carrying service for both circuit-based clients and packet-switching clients which provide a datagram service model. It can be used to carry many different kinds of traffic, including IP packets, as well as native Asynchronous Transfer Mode (ATM), Frame Relay, Synchronous Optical Networking (SONET) or Ethernet.

MPLS can exist in both an IPv4 and an IPv6 environment, using appropriate routing protocols. The major goal of MPLS development was the increase of routing speed. This goal is no longer relevant because of the usage of newer switching methods such as ASIC, TCAM and CAM-based switching able to forward plain IPv4 as fast as MPLS labeled packets. Now, therefore, the main benefit of MPLS is to implement limited traffic engineering and layer 3 or layer 2 service provider type VPNs over IPv4 networks.

MPLS is standardized by the IETF in RFC 3031. It is deployed to connect as few as two facilities to very large deployments. In practice, MPLS is mainly used to forward IP protocol data units and Virtual Private LAN Service (VPLS) Ethernet traffic. Major applications of MPLS are telecommunications traffic engineering and MPLS VPN. MPLS works in conjunction with the Internet Protocol (IP) and its routing protocols, usually interior gateway protocols (IGPs) and supports the creation of dynamic, transparent virtual networks with support for traffic engineering, the ability to transport layer VPNs with overlapping address spaces, and for layer-2 pseudowires that are capable of transporting a variety of transport payloads (IPv4, IPv6, ATM, Frame Relay, etc.).

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