MPLS Concepts

Introducing Basic MPLS Concepts

Outline

• Overview

• What Are the Foundations of Traditional IP Routing?

• Basic MPLS Features

• Benefits of MPLS

• What Are the MPLS Architecture Components?

• What Are LSRs?

• Summary

Foundations of Traditional IP Routing

• Routing protocols are used to distribute Layer 3 routing information.

• Forwarding decision is made based on:

–Packet header

– Local routing table

• Routing lookups are independently performed at every hop.

Traditional IP Routing

• Every router may need full Internet routing information.• Destination-based routing lookup is needed on

every hop.

Basic MPLS Features

• MPLS leverages both IP routing and CEF switching.

• MPLS is a forwarding mechanism in which packets are forwarded based on labels.

• MPLS was designed to support multiple Layer 3 protocols

• Typically, MPLS labels correspond to destination networks (equivalent to traditional IP forwarding).

Benefits of MPLS

• MPLS supports multiple applications including:

–Unicast and multicast IP routing

–VPN

– TE

–QoS

–AToM

• MPLS decreases forwarding overhead on core routers.

• MPLS can support forwarding of non-IP protocols.

MPLS Architecture: Control Plane

MPLS Architecture: Data Plane

MPLS Devices: LSRs

• The LSR forwards labeled packets in the MPLS domain.

• The edge LSR forwards labeled packets in the MPLS domain, and it forwards IP packets into and out of the MPLS domain.

Label Switch Routers: Architecture of LSRs

LSR Architecture Example

MPLS router functionality is divided into two major parts: the control plane and the data plane.

LSRs: Architecture of Edge LSRs

Basic MPLS Example

• MPLS core routers swap labels and forward packets based on simple label lookups.

• MPLS edge routers also perform a routing table lookup, and add or remove labels.

Summary

• Traditional IP routing forwards packets based on the destination address.

• MPLS forwards packets based on labels.

• MPLS supports multiple applications.

• MPLS has two major architectural components:

– Control plane (exchanges routing information, exchanges labels)

– Data plane (forwards packets)

• LSRs implement label exchange protocols and primarily forward packets based on labels. The role of Edge LSRs is primarily to forward packets into and out of the MPLS domain.