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.NetFlow has a flow cache that makes it possible to process access lists faster than processswitching.NetFlow also supports detailed traffic reporting that can be used for networkmanagement, planning, and departmental chargebacks.Choosing a Router PlatformYou need to provide your client with the right router platform, based on your customer srequirements.Remember to refer back to the Table 5-2 for selecting the right hardware.You willnotice that there are many variables that can affect your choice of router platform.For example, the section Provisioning a Frame Relay Network later in this chapter coversprovisioning a Frame Relay network and its equipment.The equipment choice depends directlyon various factors that are part of the implementation of Frame Relay.The problem of selecting a router in this situation is no different from the process of extractingthe customer s requirements for the new network.Identify existing equipment, define therequirements for the new network and apply them to features needed on the new equipment(performance, capacity, and scalability), and use tools to identify recommended equipment.This is a simplification of the process, but as you will see in the section for provisioning a FrameRelay network, the murkiness of choosing the equipment becomes clear when details of theimplementation are available.The router s ability to process packets quickly and efficiently will affect the router s overallperformance.Previously, many designers were concerned about the speed at which packetswere passed through the router.The following guide is a tool you can use to improve routerperformance.Merike Kaeo from the Enterprise Technical Marketing group at Cisco wrote a short guide thatprovides information on router performance, called the Router Performance Design andImplementation Guide. This guide is a strong overview on router performance and includesmany design tips, such as recognizing design flaws.This guide is included as the followingsection.It has been edited here for formatting.Router Performance Design and Implementation GuideThis Router Performance Design and Implementation Guide was originally written by MerikeKaeo from the Enterprise Technical Marketing group at Cisco.It has been edited here forformatting. CH01.book Page 172 Friday, January 7, 2000 5:35 PM172 Chapter 5: WAN DesignWith the proliferation of Cisco router products in the past few years and the ever-increasingfeatures and functionality available, understanding some of the intricate interworkings of thesedevices is necessary to design optimal performance networks.In the early days of routers, rawpacket-per-second performance was a valid concern, but with the increased improvements inprocessor power and memory management, the increasing performance numbers are reachinga point where perception and reality are becoming blurred.This paper focuses primarily on therealities of real network performance considerations and how the varying router platforms thatCisco provides can meet the appropriate criteria for any given network.The network performance considerations will not address issues regarding latency of routersbecause, in a network system as a whole, latency per switch or router has been found to benegligible when compared to normal workstation or PC disk access speeds and lower-speedmedia bandwidth considerations.It is important to note that raw performance numbers in packets per second should neverbe the sole criterion for choosing any product because criteria based on support responsiveness,company financials, feature enhancements, software reliability, troubleshooting capability, anda variety of other criteria factor heavily into a final product decision.Performance of the varyingplatforms should be understood to determine what meets the user s requirement, allowing forfuture growth and expansion of a user s network.A description of how to determine what a user s performance requirements may be follows,including some sample calculations that can then be used as a guideline and extrapolated to fitinto specific network designs.The traffic patterns and network applications may not be wellunderstood in new network designs, but it is important for some investigation to be done todetermine approximate traffic patterns and worst-case scenarios (not to be misconstrued astheoretical worst-case scenarios).Next, the switching paths of varying Cisco router platformsare listed and platform aggregate numbers are specified to help determine the most optimalplatform in a given network design scenario.The last section of the paper lists some commonfeatures that may affect switching paths and gives general guidelines for optimum networkdesigns.Realities of Network Performance CriteriaThe bottom line of any given network is that it becomes a medium whereby users (the peoplerelying on the network to do their work) accomplish their jobs without incurring any noticeabledelays.Performance criteria are met when every user is satisfied in terms of networkresponsiveness.To ensure user satisfaction, every aspect of the network must be examined,from the media to the applications to the individual devices creating the network as a whole.This task is complex. CH01.book Page 173 Friday, January 7, 2000 5:35 PMSelecting the WAN Hardware 173Differentiating Performance Tests Versus Real Network PerformanceThree areas require classification:" What comprises a performance test?" How does one interpret results?" How does one compare the results to any realistic performance requirements?The more common performance tests include blasting traffic from an input port to an outputport of a device.For a given device, injecting traffic through multiple input ports to multipleoutput ports on the same device gives aggregate performance numbers
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