Other MPLS Applications

The MPLS architecture, as discussed so far, enables the smooth integration of traditional routers and ATM switches in a unified IP backbone (IP+ATM architecture). The real power of MPLS, however, lies in other applications that were made possible, ranging from traffic engineering to peer-to-peer Virtual Private Networks. All MPLS applications use control-plane functionality similar to the IP routing control plane shown in Figure 1-6 to set up the label switching database. Figure 1-7 outlines the interaction between these applications and the label-switching matrix.

Figure 1-7. Various MPLS Applications and Their Interactions


Every MPLS application has the same set of components as the IP routing application:

  • A database defining the Forward Equivalence Classes (FECs) table for the application (the IP routing table in an IP routing application)

  • Control protocols that exchange the contents of the FEC table between the LSRs (IP routing protocols or static routing in an IP routing application)

  • Control process that performs label binding to FECs and a protocol to exchange label bindings between LSRs (TDP or LDP in an IP routing application)

  • Optionally, an internal database of FEC-to-label mapping (Label Information Base in an IP routing application)

Each application uses its own set of protocols to exchange FEC table or FEC-to-label mapping between nodes. Table 1-2 summarizes the protocols and the data structures.

The next few chapters cover the use of MPLS in IP routing; Part II, "MPLS-based Virtual Private Networks," covers the Virtual Private Networking application.

Table 1-2. Control Protocols Used in Various MPLS Applications


FEC Table

Control Protocol Used to Build FEC Table

Control Protocol Used to Exchange FEC-to-Label Mapping

IP routing

IP routing table

Any IP routing protocol

Tag Distribution Protocol (TDP) or Label Distribution Protocol (LDP)

Multicast IP routing

Multicast routing table


PIM version 2 extensions


FEC Table

Control Protocol Used to Build FEC Table

Control Protocol Used to Exchange FEC-to-Label Mapping

VPN routing

Per-VPN routing table

Most IP routing protocols between service provider and customer, Multiprotocol BGP inside the service provider network

Multiprotocol BGP

Traffic engineering

MPLS tunnels definition

Manual interface definitions, extensions to IS-IS or OSPF


MPLS Quality of Service

IP routing table

IP routing protocols

Extensions to TDP



    Part 2: MPLS-based Virtual Private Networks