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This chapter provides an overview of Multilayer Switching (MLS) and is divided into these sections:
MLS provides high-performance Layer 3 switching for the Catalyst 5000 series LAN 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 (EIGRP), Routing Information Protocol (RIP), and Intermediate System-to-Intermediate System
(IS-IS), are used for route determination.
The Route Switch Module (RSM) performs route processing and central configuration and control for the Catalyst 5000 series switch. Routing services can also be provided by an externally attached router.
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.
MLS consists of the following:
Detailed procedures for configuring MLS and NDE are provided in Chapter 3, "Configuring Multilayer Switching."
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.
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.
Refer to Chapter 2, "Network Implementation" for a detailed description of MLS flows.
MLS allows you to monitor all intersubnet traffic through the NFFC and the RSM (or externally attached router). This feature complements the embedded Remote Monitoring (RMON) capabilities on the Catalyst 5000 series switch that allow you to see all port traffic.
Integrated MLS management includes products, management utilities, and partner applications designed to gather flow statistics, export the statistics, collect and perform data reduction on the exported statistics, and forward them to consumer applications for traffic monitoring, planning, and accounting. Flow collectors, such as the Cisco SwitchProbe and NetFlow FlowCollector, gather and classify flows. This flow information is then aggregated and fed to consumer applications such as TrafficDirector, NetSys, or NetFlow Analyzer.
We recommend the Cisco SwitchProbe device as the flow collector for MLS. The SwitchProbe device supports the two versions of data (Versions 1 and 7) exported from the RSM and NFFC using NDE. SwitchProbe proxies the data to RMON2 for viewing from the TrafficDirector application. Support is also included for the RMON2 Management Information Base (MIB) group.
Refer to the SwitchProbe Installation and Configuration Guide located on the CD-ROM that shipped with your Catalyst 5000 series product for information about SwitchProbe. Additional information for all of the management applications can be found on the
CD-ROM.
An external data collector gathers flow entries from the MLS cache of one or more
Catalyst 5000 series switches or routers. The switch or router transmits data to the flow collector by grouping flow entries for expired flows from its MLS cache into a User Datagram Protocol (UDP) datagram, which consists of a header and a series of flow entries. The gathered flow statistics enable several key customer applications and benefits illustrated in Figure 1-1 and described in the sections that follow.
MLS data allows you to understand your users' utilization of network and application resources. With this information, you can efficiently plan and allocate access, backbone, and application resources as well as detect and resolve potential security and policy violations. For example, you can use MLS data to deduce the Top N Talkers between a pair of subnets using the TrafficDirector application. (Top N Talkers is a graphical display in the TrafficDirector application that lists the top 20 talkers on a network segment.)
MLS data allows you to view application traffic patterns over the network. Content providers may utilize this information to plan and allocate network and application resources (such as Web server sizing and location) to meet customer demands. For example, the network administrator can see the percentage of traffic used by the Web, File Transfer Protocol (FTP), Telnet, and other Transmission Control Protocol/Internet Protocol (TCP/IP) applications.
MLS data allows you to monitor your network. With MLS, you can use RMON,
RMON2, and flow-based analysis techniques to visualize traffic patterns associated with individual switches as well as on a network-wide basis.
MLS data allows you to make both strategic network planning (such as backbone upgrade planning, routing, and policy planning), and tactical network engineering decisions (such as adding additional line cards to switches and upgrading link capacity) that minimize the total cost of network operations while maximizing network performance, capacity, and reliability.
MLS data provides you with metering (flow data includes details such as IP addresses, packet and byte counts, timestamps, application ports, and so on) information for flexible resource utilization accounting.
MLS allows you to debug and trace flows in your network. It enables you to identify which switch is handling a particular flow by using MLS explorer packets (initialized through the debug mls rp locator command), which aids you in path detection and troubleshooting.
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