Specifications

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Multilayer Switching Overview

This chapter provides an overview of Multilayer Switching (MLS).

Note The information in this chapter is a brief summary of the information contained in the Catalyst 5000

Series Multilayer Switching User Guide. The commands and configurations described in this guide apply

only to the devices that provide routing services. Commands and configurations for Catalyst 5000 series

switches are documented in the Catalyst 5000 Series Multilayer Switching User Guide.

MLS provides high-performance Layer 3 switching for Cisco routers and switches. MLS switches IP

data packets between subnets using advanced application-specific integrated circuit (ASIC) switching

hardware. Standard routing protocols, such as Open Shortest Path First (OSPF), Enhanced Interior

Gateway Routing Protocol (Enhanced IGRP), Routing Information Protocol (RIP), and Intermediate

System-to-Intermediate System (IS-IS), are used for route determination.

MLS enables hardware-based Layer 3 switching to offload routers from forwarding unicast IP data

packets over shared media networking technologies such as Ethernet. The packet forwarding function is

moved onto Layer 3 Cisco series switches whenever a partial or complete switched path exists between

two hosts. Packets that do not have a partial or complete switched path to reach their destinations still

use routers for forwarding packets.

MLS also provides traffic statistics as part of its switching function. These statistics are used for

identifying traffic characteristics for administration, planning, and troubleshooting. MLS uses NetFlow

Data Export (NDE) to export the flow statistics

Procedures for configuring MLS and NDE on routers are provided in the “Configuring IP Multilayer

Switching” chapter.

Procedures for configuring MLS and NDE on routers are provided in the following chapters in this

publication:

• “Configuring IP Multilayer Switching” chapter

• “Configuring IP Multicast Multilayer Switching” chapter

• “Configuring IPX Multilayer Switching” chapter

This chapter describes MLS. It contains the following sections:

• Terminology

• Introduction to MLS