Chapter 1. Introduction

Multiprotocol Label Switching (MPLS) is over 10 years old. Born at a time when the Internet had just become a household word, MPLS had a hugely enthusiastic childhood and rapidly became one of the hottest buzzwords in the networking industry. Deployment, however, followed much more cautiously, and it was some years before MPLS saw wide rollout to carry live traffic in real operators’ networks. MPLS can certainly now be said to be a mature technology with extensive deployments around the world, and with new applications and enhancements being invented all the time.

Unlike some of its precursors (such as ATM and Frame Relay), MPLS deployments have seen extensive use of the control plane right from the very start. In part, that can be attributed to the fact that MPLS leveraged many already-mature control plane protocols from the TCP/IP suite of protocols, notably the routing protocols BGP, OSPF, and IS-IS. At times, it seemed that MPLS might suffer from a surplus of control plane protocols when the Constraint-based Routed Label Distribution Protocol (CR-LDP) and Traffic Engineering extensions to the Resource Reservation Protocol (RSVP-TE) were both fighting for the same role as members of the MPLS control plane to support constraint-based routing.