Chapter 24. MPLS

In my experience, there are two levels of involvement with MPLS (Multiprotocol Label Switching) networks. First, there are people who design and maintain the MPLS networks themselves. These people generally work for service providers such as AT&T, British Telecom, and the like. Second are the people who need to use MPLS in their corporate WANs. This chapter is written for the latter category—the people who need to employ an MPLS solution in their networks, not the people who actually design them. Why? Because the target audience for this book is composed mostly of the people who work with corporate networks on a daily basis. My goal is not to help you build an MPLS network from the ground up, it’s to help you deploy MPLS as handed to you from a provider. As a result, you will not see a lot of jargon like penultimate hop popping (possibly my favorite tech term ever) used here. Really, you don’t need to know this to make an MPLS WAN work for you. My goal, as always, is to help you get your job done.

In a nutshell, packets in an MPLS network are prefixed with an MPLS header (called a label stack). This header contains one or more labels, each of which contains a label value, a traffic-class field (used for quality of service [QoS]), a bottom-of-stack flag, and an 8-bit time-to-live (TTL) field. Sounds exciting, doesn’t it? For most people using MPLS, none of this matters. Bear with me, though, because you need to understand some history.

The label stack is the only thing ...

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