MPLS in the SDN Era

Chapter 2. The Four MPLS Builders

Depending on the function of a Multiprotocol Label Switching (MPLS) label, it can receive many names: transport label, service label, VPN label, entropy label, and so on. This chapter focuses on the original and primary function of MPLS labels: the transport of data packets through a labeled tunnel.

Chapter 1 describes how MPLS tunnels are provisioned by using a static label-mapping technique. However, this approach is limited in terms of scalability, operability, failure detection, and redundancy. There is fortunately a classic solution at hand: signaling the tunnels with protocols that create MPLS paths in a dynamic manner. What protocols? There are actually a few of them, each with their pros and cons.

This chapter covers the following alternatives:

• Two pure MPLS signaling protocols: Label Distribution Protocol (LDP) and Resource Reservation Protocol with Traffic Engineering (RSVP-TE)

• The modern MPLS extensions of classic IP routing protocols: Border Gateway Protocol (BGP), Intermediate System–to–Intermediate System (IS-IS), and Open Shortest-Path First (OSPF)

BGP has had MPLS extensions since the early times, and they keep evolving. As for IS-IS and OSPF, their MPLS extensions have come more recently with a technology called SPRING or Segment Routing. SPRING, which was still in IETF draft state at the time of the publication of this book, also has extensions for BGP.

The four MPLS Builders are therefore: LDP, RSVP-TE, BGP, and the Interior ...