Specifications

Multilayer Switching Overview

Terminology

• Key MLS Features

• MLS Implementation

• Standard and Extended Access Lists

• Introduction to IP Multicast MLS

• Introduction to IPX MLS

• Guidelines for External Routers

• Features That Affect MLS

Terminology

The following terminology is used in the MLS chapters:

• Multilayer Switching-Switching Engine (MLS-SE)—A NetFlow Feature Card (NFFC)-equipped

Catalyst 5000 series switch.

• Multilayer Switching-Route Processor (MLS-RP)—A Cisco router with MLS enabled.

• Multilayer Switching Protocol (MLSP)—The protocol running between the MLS-SE and MLS-RP

to enable MLS.

Introduction to MLS

Layer 3 protocols, such as IP and Internetwork Packet Exchange (IPX), are connectionless—they deliver

each packet independently of each other. However, actual network traffic consists of many end-to-end

conversations, or flows, between users or applications.

A flow is a unidirectional sequence of packets between a particular source and destination that share the

same protocol and transport-layer information. Communication from a client to a server and from the

server to the client is in separate flows. For example, HTTP Web packets from a particular source to a

particular destination are in a separate flow from File Transfer Protocol (FTP) file transfer packets

between the same pair of hosts.

Flows can be based on only Layer 3 addresses. This feature allows IP traffic from multiple users or

applications to a particular destination to be carried on a single flow if only the destination IP address is

used to identify a flow.

The NFFC maintains a Layer 3 switching table (MLS cache) for the Layer 3-switched flows. The cache

also includes entries for traffic statistics that are updated in tandem with the switching of packets.

After the MLS cache is created, packets identified as belonging to an existing flow can be

Layer 3-switched based on the cached information. The MLS cache maintains flow information for all

active flows. When the Layer 3-switching entry for a flow ages out, the flow statistics can be exported

to a flow collector application.

For information on multicast MLS, see the “Introduction to IP Multicast MLS” section in this chapter.

Key MLS Features

Table 37 lists the key MLS features.