Cisco Systems RJ-45-to-AUX manual MLS Components, Prioritizing Traffic Flows, 228

manner. This method is similar to sending a piece of mail: You put it in the mailbox, but you have no guarantee that it will arrive—just the likelihood it will reach its destination.

Using other protocols, including those at Layer 2 and Layer 4, the network traffic is made up of a series of end−to−end conversations also known as flows. These flows are connection−oriented in nature. Connection−oriented data traffic is similar to a certified letter. You put the letter in the mailbox, and you receive a signed notice saying the letter reached its destination.

MLS identifies network flows from a network source to a network destination by using the Network and Transport layer information in the packet headers; it then forwards the packets. This sequence of packets is sent in one direction between a particular source and destination and uses the same protocol and Layer 4 header information.

Let’s take a look at multiple flows. Suppose I am looking at Coriolis’s Web site to determine when the last book I wrote will be released. At the same time, I am using FTP to send the latest chapter I have written for review. Both data flows are traversing back and forth from the same source to the same destination and vice versa—two flows of data are traveling at the same time between my PC and a server at Coriolis. How does my host, a router, or even the switch know which conversation I want on my screen? Why don’t parts of the Coriolis Web site get mixed into the chapter I am uploading? The reason it works is that each flow is assigned an individual port number.

MLS should not be confused with NetFlow switching provided by the NetFlow Feature Card (NFFC) or the NFFC II, even though the NFFCs are used to provide MLS with the Catalyst 5000 and 6000 families of switches. MLS must use an external router or an internal route processor such as the Route Switch Module (RSM) to provide the routing resolution for the initial packet that is routed in an MLS flow (the connection−oriented session). Each subsequent packet in the flow is processed by the switch, not the router.

Prioritizing Traffic Flows

MLS identifies the unique flows between hosts by identifying the user application and classifying data traffic with the appropriate priority level. These flows can be either unicast or multicast traffic.

MLS identifies individual network traffic flows to provide predictable network services. It does this by supplying dedicated bandwidth to those applications that need it most. As an example, enterprise resource planning (ERP) application traffic (which can be mission−critical) can be identified as needing a higher priority and thus receive more network bandwidth than, say, Web or FTP traffic.

Before we go into more detail on packet flows, let’s take a more detailed look at the hardware and software used by MLS.

MLS Components

You should understand three components in the MLS process to resolve the destination path for the initial packet flow. These components are required in order to use MLS and send routing updates to Catalyst switches. The components are as follows:

∙MLS Switching Engine (MLS−SE)—The switch supporting MLS

∙MLS Route Processor (MLS−RP)—The internal route processor in the switch or external router that supports MLS

∙Multilayer Switch Protocol (MLSP)—The protocol that runs between the MLS−SE and MLS−RP to enable MLS

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