JUNOS Cookbook

Chapter 14. MPLS

Introduction

Multiprotocol Label Switching ( MPLS), as its name implies, is a switching protocol developed by the IETF to incorporate some of the benefits of network switching devices into an IP network. MPLS is designed to work with standard IP routing protocols—BGP, OSPF, and IS-IS—which have been extended to support MPLS.

Work on MPLS started as a response to the development of the Asynchronous Transfer Mode (ATM) protocol by the ITU and the ATM Forum in the late 1980s and early 1990s, and the propagation of ATM switches. By the early 1990s, the performance of ATM switches exceeded that of IP routers, but the architectural model, which is based on virtual circuits (a connection model) fundamentally differed from the IP connectionless model. In the early 1990s, it seemed that ATM-based applications might become dominant. However, when TCP/IP-based applications, such as the World Wide Web, became standard, the ATM Forum and the IP standards bodies designed a number of schemes, sometimes fairly complex, that allowed ATM and IP protocols to interoperate. The IETF borrowed a number of ATM switching design features when designing MPLS.

In response to ATM, several router vendors developed switching technologies compatible with IP routing. IPsilon, a now defunct startup, created IP Switching, Toshiba developed a Cell Switching Router (CSR), IBM introduced an approach called Aggregate Route-based IP Switching (ARIS), and Cisco Systems had Tag Switching. Cisco pursued ...