Introduction to MPLS. Explaining Multi-Protocol Label Switching

Conceived and developed in the late '90s by the Internet Engineering Task Force, MPLS, or Multi-Protocol Label Switching is a network management protocol originally intended to integrate layer 2 information about network links (bandwidth, latency, utilization) into layer 3 (IP) elements within a particular system.

While traditional IP networks have no means of labeling, categorizing or monitoring the packets that traverse them, MPLS technology works to solve those IP shortcomings, placing labels on IP packets and providing that labeling function. And because MPLS is an overlay protocol it can operate over top of the IP protocol in the same network without interference. MPLS is not designed to replace IP. Rather, it is designed to add a set of rules to IP so that traffic can be classified, marked and policed.

MPLS-equipped networks use MPLS-aware devices known as label edge routers (LERs), positioned at the network’s edges. These devices are designed to inspect IP packets entering the network and add MPLS headers, as well as removing the headers from packets leaving the MPLS network. Inside the boundaries of the MPLS network, devices known as label switch routers (LSRs) look for an MPLS label on each packet that passes through them, looking up and following the instructions contained in those labels, routing them based on a list of instructions.

MPLS allows administrators to define routes known as label switched paths (LSPs) from one LER to another, through a series of LSRS, across the MPLS network. These LSPs are pre-assigned and pre-engineered paths that packets with a certain label should follow.

One of the most obvious advantages of MPLS is that it provides network administrators with a number of tools for traffic engineering. An MPLS network can offer the same sort of quality of service guarantees that data transport services like Frame Relay or ATM can, without requiring the use of any dedicated lines. An administrator, for example, can define a LSP that ensures VoIP traffic will be routed through the most reliable, highest performing sections of the network while less critical traffic, such as email, is sent across the slower sections.

The reason MPLS technology is contributing to the rapid growth of the virtual private networking market is that it provides service providers and network operators with a simpler means of adding VPN technology to their portfolios, and a simpler means of provisioning VPNs to their customers. Because MPLS allows service providers to create new virtual private networks without having to install new hardware, it significantly reduces the cost of implementation, which in turn reduces the overall cost of VPNs. And reduced cost is possibly the largest motivator in the migration from more infrastructure-heavy private networking.

While most of the benefits of MPLS lie on the service provider side of the network, there are results of the MPLS architecture that have direct benefits for the customer. MPLS-based service provider edge equipment is designed to communicate with customer premises equipment (CPE) in a standards-based environment, removing the need for customers to deploy new equipment, and protecting CPE investments.

Though MPLS is best suited to the needs of large-scale network operators, its implementation can benefit a range of network users, from service providers themselves, to enterprises and even small- and medium-sized businesses, with the ever-increasing functionality and cost-effectiveness of data transport services.