Benefits and Uses of Multilayer Switches

The multilayer switch is both faster and less expensive than a standalone router. These attributes make multilayer switches an attractive way to supplement a premise-edge router. Its best use is as a front end to an interior gateway router in a modified form of collapsed backbone LAN. Figure 15-3 illustrates this.

Figure 15-3: A multilayer switch reduces the workload of the interior gateway router.

Figure 15-3: A multilayer switch reduces the workload of the interior gateway router.

This arrangement features the following division of responsibilities:

• The hardware-based router is used as a gateway between the LAN and the internetwork beyond.

• The less-expensive IP switch helps reduce the workload of that interior gateway router by functioning as a collapsed backbone switch.

The Future of Routing

In this arrangement, the only datagrams that would be passed from the IP switch to the router would be those addressed to destinations that lie beyond the local LAN. All communications between clients and servers (which reside on separate LAN segments) would be spared the hop through the standalone router. There are three main benefits to using this configuration:

• The efficiency of the standalone router is greatly increased because its workload is limited to just WAN access functions.

• The cost per-port of LAN switches tends to be substantially less than the cost of a comparable router port. Reducing the router's workload may also enable the use of a smaller, less-expensive router.

• The efficiency of LAN-to-LAN communication is also increased, because the multilayer switch operates much faster than a traditional router in a collapsed backbone LAN.

After examining the benefits and limitations of multilayer switches, there can only be one conclusion: They are a wonderful complement to a standalone router in very large LAN environments.

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