What is MPLS?

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What is MPLS?

MPLS is an IP-based Layer 3 networking technology developed in the late 1990s. It replaced Frame-Relay and ATM based Layer 2 networks prevalent at the time.

MPLS stands for Multi-Protocol Label Switching, and uses a tag attached to the packet by the network service provider to indicate to their network where to send the traffic. It provides virtualised Layer 3 routing within the service-providers network, segregating your traffic from other customers in separate routing tables.

Why is it better?

MPLS improves traffic-flow by eliminating the data sent through intermediate sites. This now happens earlier in the provider network, and has big impacts for latency and jitter; which is key for voice-over-IP technologies; as well as for bandwidth, as you don’t carry traffic at the central hubs for other sites.

Who administers and standardises it?

The IETF mpls group, part of the routing area, administers the industry standards. RFC3031 covers the basic MPLS infrastructure, and RFC4364 covers the use of BGP routing to create individual and segregated VPNs within the infrastructure.

How does it work?

The architecture consists of Customer Edge (CE) routers, which send data into the service providers network. The CE router sends data into the service-provider network to the Provider Edge router. This has a routing table for the customer, and selects the destination. This is the PE to which the destination CE attaches and adds a label to the packet. The central provider (P) routers switch packets, using the tag that the first PE router added.. The tag has the ID of the destination PE router at the far side of the network. This reduces the workload of the central provider (P) routers, meaning they can now forward packets faster.

There is nothing special or different about CE devices, and no labelling of the packets occurs at this point. (Indeed, many service providers are moving to device-less edges, with the functions previously carried out in their CE router equipment now being done by Layer 3 switches in the customer network.)

What of the future?

Developments expanded MPLS to support MPLS-TE (traffic engineered links within the network), as well as to carry Layer 2 traffic in EoMPLS.