Multiprotocol Label Switching (MPLS)

It is a protocol for routing traffic within a telecommunications network, as data travels from one network node to the next. MPLs can provide applications including VPNs and Quality of Service (QoS). MPLs allows most data packets to be forwarded at Layer-2 --the switching level. In traditional IP routing, each router determines a packet's next hop by inspecting the packet's destination IP before consulting its own routing table. The router's forwarding tables contain information on the network topology, obtained via an IP routing protocol, such as OSPF, IS-IS, BGP, RIP or static configuration, which keeps that information synchronized with changes in the network. This process consumes time and hardware resources. However, in an MPLs network, the very first router to receive a packet determines the packet's entire route up front. This identity is conveyed to subsequent routers using a label in the packet header.

L in MPLS stands for Labels. Operating between layer 2 & 3, a label is a 4-BYTE (32-BIT). This identifies the packet's entire route in a MPLS network. Labels can also contain information related to Quality of service, indicating a packet's priority level.

Unlike traditional IP routing, MPLS flows are connection-oriented and packets are routed along pre-configured Label Switcher Paths (LSPs).

How Does MPLS work ?

Think of MPLS like mailing a package:

For most connections, networks need to look inside every data packet at each router to know where it’s going. It’s like having to look inside a shipped package at every post office along the way to find out its final destination.

An ingress router with MPLS will label data packets (mail packages) on entry to the network (post office), so routers (mail workers) know exactly where the data is going without having to open the package again and again. -- credit: itel.com