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.Internetworking Design Basics 2-35 Identifying and Selecting Internetworking DevicesNetwork managers are adding LAN switches to their wiring closets to augment bandwidth andreduce congestion in existing shared-media hubs while using new backbone technologies, such asFast Ethernet and ATM.LAN SwitchesToday s cost-effective, high-performance LAN switches offer network managers the followingbenefits:" Superior microsegmentation" Increased aggregate data forwarding" Increased bandwidth across the corporate backboneLAN switches address end users bandwidth needs for wiring closet applications.By deployingswitches rather than traditional shared hubs, network designers can increase performance andleverage the current investments in existing LAN media and adapters.These switches also offerfunctionality not previously available, such as VLANs, that provide the flexibility to use software tomove, add, and change users across the network.LAN switches are also suited to provide segment switching and scalable bandwidth within networkdata centers by delivering switched links to interconnect existing hubs in wiring closets, LANswitches, and server farms.Cisco provides the Catalyst family of multilayer switches for connectingmultiple wiring closet switches or shared hubs into a backbone configuration.ATM SwitchesEven though all ATM switches perform cell relay, ATM switches differ markedly in the followingcapabilities:" Variety of interfaces and services that are supported" Redundancy" Depth of ATM internetworking software" Sophistication of traffic management mechanismJust as there are routers and LAN switches available at various price/performance points withdifferent levels of functionality, ATM switches can be segmented into the following four distincttypes that reflect the needs of particular applications and markets:" Workgroup ATM switches" Campus ATM switches" Enterprise ATM switches" Multiservice access switchesCisco offers a complete range of ATM switches.Workgroup and Campus ATM SwitchesWorkgroup ATM switches have Ethernet switch ports and an ATM uplink to connect to a campusATM switch.An example of a workgroup ATM switch is the Cisco Catalyst 5000.Campus ATM switches are generally used for small-scale ATM backbones (for example, to link ATMrouters or LAN switches).This use of ATM switches can alleviate current backbone congestion andenable the deployment of such new services as VLANs.Campus switches need to support a wide2-36 Cisco CCIE Fundamentals: Network Design Switches and Routers Comparedvariety of both local backbone and WAN types, but be price/performance optimized for the localbackbone function.In this class of switches, ATM routing capabilities that allow multiple switchesto be tied together is very important.Congestion control mechanisms for optimizing backboneperformance is also important.The LightStream 1010 family of ATM switches is an example of acampus ATM switch.For more information on deploying workgroup and campus ATM switches inyour internetwork, see Chapter 12, Designing Switched LAN Internetworks. Enterprise ATM SwitchesEnterprise ATM switches are sophisticated multiservice devices that are designed to form the corebackbones of large, enterprise networks.They are intended to complement the role played by today shigh-end multiprotocol routers.Enterprise ATM switches are used to interconnect campus ATMswitches.Enterprise-class switches, however, can act not only as ATM backbones but can serve asthe single point of integration for all of the disparate services and technology found in enterprisebackbones today.By integrating all of these services onto a common platform and a common ATMtransport infrastructure, network designers can gain greater manageability and eliminate the need formultiple overlay networks.Cisco s BPX/AXIS is a powerful broadband ATM switch designed to meet the demanding,high-traffic needs of a large private enterprise or public service provider.For more information ondeploying enterprise ATM switches in your internetwork, see Chapter 8, Designing ATMInternetworks. Multiservice Access SwitchesBeyond private networks, ATM platforms will also be widely deployed by service providers both ascustomer premises equipment (CPE) and within public networks.Such equipment will be used tosupport multiple MAN and WAN services for example, Frame Relay switching, LANinterconnect, or public ATM services on a common ATM infrastructure.Enterprise ATM switcheswill often be used in these public network applications because of their emphasis on high availabilityand redundancy, their support of multiple interfaces, and capability to integrate voice and data.Switches and Routers ComparedTo highlight the differences between switches and routers, the following sections examine thedifferent roles of these devices in the following situations:" Implementation of VLANs" Implementation of switched internetworksRole of Switches and Routers in VLANsVLANs address the following two problems:" Scalability issues of a flat network topology" Simplification of network management by facilitating network reconfigurations (moves andchanges)A VLAN consists of a single broadcast domain and solves the scalability problems of large flatnetworks by breaking a single broadcast domain into several smaller broadcast domains or VLANs.Virtual LANs offer easier moves and changes in a network design than traditional networks.LANswitches can be used to segment networks into logically defined virtual workgroups.This logicalsegmentation, commonly referred to as VLAN communication, offers a fundamental change in howInternetworking Design Basics 2-37 Identifying and Selecting Internetworking DevicesLANs are designed, administered, and managed
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