Read an Excerpt
CCNP Remote Access Exam Certification Guide : Exam #640-505
Chapter 1: All About the Cisco Certified Network and Design Professional CertificationsThe Cisco Certified Network Professional (CCNP) and the Cisco Certified Design Professional (CCDP) certifications prove that an individual has completed rigorous testing in the network arena. In addition, the CCNP and CCDP certifications are becoming more important than ever because Cisco is providing greater and greater incentives to their partners that have employees with CCNP- and CCDP-level expertise.
The CCNP and CCDP tracks require the candidate to be comfortable with advance routing techniques, switching techniques, and dial-up or Remote Access Server (RAS) technology. On top of those areas, the CCNP must be able to, without a book, configure and troubleshoot a routed and switched network. In addition, the CCDP must digest a vast quantity of user requirements and prepare a scalable design that fits the customer needs and requirements.
The CCNP is a hands-on certification that requires a candidate to pass the Cisco Internetwork Troubleshooting exam, which is also called the Support exam. The emphasis in the exam is on troubleshooting the router if the configuration for it has failed. CCNP is currently one of the most sought after certifications, short of the Cisco Certified Internetworking Expert (CCIE).
The CCDP track focuses on designing scaleable networks using routing and switching technologies. The exam places heavy emphasis on the interplay between routed and routing protocols. This track has a more theoretical final exam-the Cisco Internetwork Design (CID) exam. This certification is veryimportant to the pre-sales engineer and the design engineer who want to prepare a network on paper, but who do not want to focus on the minor details of the syntax within the router.
Because both the CCNP and CCDP certifications are the same except for the final test, it should not be suprising that a CCNP can produce a solid, scalable design and that a CCDP can configure a router. The core issue between the certifications is the focus that the candidate wants to take into the business world.
The CCNP and CCDP tracks are daunting at first glance because they both require a number of tests. To become a CCNP or CCDP, a candidate must first be a Cisco Certified Network Associate (CCNA). The CCNP and CCDP certifications require study and proficiency in the three areas of advanced routing, in switching and RAS, and a specialization in either design or troubleshooting.
Neither CCNP or CCDP certification is a "one test and I'm home" exam. Each exam for these certifications is difficult in its own right because of the depth of understanding needed for each area of concentration. The focus of this book is the preparation for and passing of the CCNP/CCDP Remote Access Exam.
Some of the information in this book overlaps with information in the routing field, and you may have seen some of this book's information while studying switching. In addition, there are other certification books that specifically focus on advanced routing and switching. You might find some overlap in those manuals also. This is to be expected-all the information taken as a whole is what produces a CCNP or CCDP
The exam is a computer-based exam that has multiple choice, fill-in-the-blank, and list-in-order style questions. The fill-in-the-blank questions are filled in using the complete syntax for the command, including dashes and the like. For the fill-in-the-blank questions, a tile button is given to list commands in alphabetical order. This is a real life saver if you can't remember if there is a dash or an "s" at the end of a command. Knowing the syntax is key, however, because the list contains some bogus commands as well as the real ones.
The exam can be taken at any Sylvan Prometric testing center (1-800-829-NETS or www.2test.com). The test has 62 randomly generated questions, and you have 90 minutes to complete it. As with most Cisco exams, you cannot mark a question and return to it. In other words, you must answer a question before moving on, even if this means guessing. Remember that a blank answer is scored as incorrect.
Most of the exam is straightforward; however, the first answer that leaps off the page can be incorrect. You must read each question and each answer completely before making a selection. If you find yourself on a question that is incomprehensible, try restating the question a different way to see if you can understand what is being asked. Very few candidates score 100 percent in all catagories-the key is to pass. Giving up just one question because of lack of diligence can mean the difference between passing and failing because there are so few questions. Four questions one way or the other can mean a change of 10-20 percent!!
Many people do not pass on the first try, but success is attainable with study. This book includes questions and scenarios that are designed to be more difficult and more in depth than most questions on the test. This was not done to show how much smarter we are, but to allow you a certain level of comfort when you have mastered the material in this book.
The CCNP and CCDP certifications are difficult to achieve, but the rewards are there, and will continue to be there, if the bar is kept where it is.
How This Book Can Help You Pass the CCNP Remote Access Exam
The primary focus of this book is not to teach material in the detail that is covered by an instructor in a five-day class with hands-on labs. Instead, we tried to capture the essence of each topic and to present questions and scenarios that push the envelope on each topic that is covered for the Remote Access test.
The audience for this book includes candidates that have successfully completed the Building Cisco Remote Access Networks (BCRAN) class and those that have a breadth of experience in this area. The show and debug commands from that class are fair game for questions within the Remote Access exam, and hands-on work is the best way to commit those to memory.
If you have not taken the BCRAN course, the quizzes and scenarios in this book should give you a good idea of how prepared you are to skip the class and test out based on your experience. On the flip side, however, you should know that although having the knowledge from just a classroom setting can be enough to pass the test, some questions assume a CCNA-level of internetworking knowledge.
Overview of Cisco Certifications
Cisco fulfills only a small portion of its orders through direct sales; most times, a Cisco reseller is involved. Cisco's main motivation behind the current certification program was to measure the skills of people working for Cisco Resellers and Certified Partners.
Cisco has not attempted to become the only source for consulting and implementation services for network deployment using Cisco products. In 1996 and 1997 Cisco embarked on a channel program in which business partners would work with smaller and midsized businesses with whom Cisco could not form a peer relationship. In effect, Cisco partners of all sizes carried the Cisco flag into these smaller companies. With so many partners involved, Cisco needed to certify the skill levels of the employees of the partner companies.
The CCIE program was Cisco's first cut at certifications. Introduced in 1994, the CCIE was designed to be one of the most respected, difficult-to-achieve certifications. To certify, a written test (also at Sylvan Prometric) had to be passed, and then a two-day hands-on lab test was administered by Cisco. The certifications were a huge commitment for the smaller resellers that dealt in the commodity-based products for small business and home use.
Cisco certified resellers and services partners by using the number of employed CCIEs as the gauge. This criterion worked well originally, partly because Cisco had only a few large partners. In fact, the partners in 1995-1997 were generally large integrators that targeted the midsized coporations with whom Cisco did not have the engineering resources to maintain a personal relationship. This was a win-win situation for both Cisco and the partners. The partners had a staff that consisted of CCIEs that could present the product and configuration with the same adroitness as the Cisco engineering staff and were close to the customer.
Cisco used the number of CCIEs on staff as a criterion in determining the partner status of another company. That status in turn dictated the discount received by the reseller when buying from Cisco. The number of resellers began to grow, however, and with Cisco's commitment to the lower-tier market and smaller-sized business, it needed to have smaller integrators that could handle that piece of the market.
The CCIE certification didn't help the smaller integrators who were satisfying the small business and home market; because of their size, the smaller integrators were not able to attain any degree of discount. Cisco, however, needed their skills to continue to capture the small business market, which was-and is-one of the largest markets in the internetworking arena today.
What was needed by Cisco was a level of certification that was less rigorous than CCIE but that would allow Cisco more granularity in judging the skills on staff at a partner company. So Cisco created several additional certifications, CCNP and CCDP included.
Two categories of certifications were developed-one to certify implementation skills and the other to certify design skills. Service companies need more implementation skills, and resellers working in a pre-sales environment needed more design skills. So the CCNA and CCNP are implementation-oriented certifications; whereas, the Cisco Certified Design Associate (CCDA) and CCDP are design-oriented certifications.
Rather than just one level of certification besides CCIE, Cisco created two additional levelsAssociate and Professional. CCNA is more basic, and CCNP is the intermediate level between CCNA and CCIE. Likewise, CCDA is more basic than CCDP.
Several certifications require other certifications as a prerequsite. For instance, CCNP certification requires CCNA first. Also, CCDP requires both CODA and CCNA certification. CCIE, however, does not require any other certification prior to the written and lab tests. This is mainly for historical reasons.
Cisco certifications have become a much needed commodity in the internetworking world as companies scramble to position themselves with the latest e-commerce, e-business, and e-life that is out there. Because Novell, Windows NT, Linux, or any other routed protocols generally need to be routed somewhere, the integrators want a piece of that business as well. Because Cisco cannot form a relationship with every new startup business, it looks for certified partners to take on that responsibility. The CCNP and CCDP certifications are truly another win-win situation for resellers, integrators, you, and Cisco...
CCNP Routing Exam Certification Guide
Chatper 1: Cisco Certifications, the Routing Exam, and This Book's Features
The Cisco Certified Network Professional (CCNP) and Cisco Certified Design Professional (CCDP) certifications on the Routing and Switching career track are becoming increasingly popular. These certifications have as their foundation the Cisco Certifed Network Associate (CCNA) certification and these profesional-level certifications form the second rung in the ladder to the coveted Cisco Certified Internetwork Expert (CC1E) certification. The Routing 2.0 exam (#640-503) is one of three exams that you must pass to become a CCNP or CCDP. This book will help you prepare for that exam. Professional-level certification opens doors to career opportunities and is a prerequisite for other Cisco certifications as well. Generally, passing the Routing 2.0 exam means that you have mastered the concepts and implementation skills necessary to build a complex IP network of Cisco routers.
You must pass the Routing 2.0 exam (among other exams) to acheive either the CCNP or the CCDP certification. The CCNP and CCDP certifications are often referred to as the professional-level certifications throughout this book wherever the information at hand applies to CCNP and CCDP. For more information on the differences between the two professional-level certifications and the latest on Cisco exams and certifications, begin at the Cisco Career Certification page (www.cisco.coin/warp/public/ 10/wwtraining/certprog/ index.html) at Cisco Connection Online (CCO).
The Routing exam is a computer-based exam, with multiple-choice, fill-in-the-blank, and list-in-order style questions. The exam can be taken at any Sylvan Prometric testing center (1-800-829-NETS, www.2test.com). The exam will take about 75 minutes and has approximately 60 questions. You should check with Sylvan Prometric for the exact length of the exam. (Be aware that when you register for the exam, you might be told to allow a certain amount of time to take the exam that is longer than the testing time indicated by the testing software when you begin. This is because Sylvan Prometrics wants you to allow for some time to get settled and take the tutorial on the testing engine.)
This book uses the terms Routing exam and Routing 2.0 exam. These terms are used synonomously and refer to the the exam #640-503.
The Routing 2.0 exam is not an easy exam. This is to say that you cannot simply read one book and expect to pass it. In fact, the exam is surprisingly difficult; this is so that Cisco can be sure that everyone who passes the test thoroughly understands the subject matter on a conceptual level and is not just good at exams. More importantly, Cisco is very interested in making sure that passing proves that you have the skills to actually implement the features, not just talk about them. The exam is difficult in subject matter and also in format. You can expect multiplechoice questions-some with multiple answers. You can also expect questions requiring you to pick the correct answer from output screens and configurations. Another difficult aspect of the exam format is that, to ensure that you know your stuff, the exam does not allow you to go back and change an answer. Those CCNP/CCDP candidates who are unsure about the question will be forced to guess rather than have an extra 15 minutes to think about it at the end of the exam. Those who really know most of the answers will be rewarded by Cisco's attempts to preserve the integrety of the CCNP/CCDP certification. The professional-level certification will mean to all that you are highly qualified at the subject at hand.
Although this is a difficult exam, most networking professionals can expect to pass if they meet the prerequisites and spend the proper amount of time on training, on-the-job experience, and study. Like most certification exams, you might not pass the first time. Taking the exam a second time, however, might be easier because you have an idea of what to expect.
There are many questions on the Routing 2.0 exam that you might already know through your professional background and experiences, if you meet the prerequisites. This book offers you the opportunity to solidify and build on that knowledge as you make your final preparations to take the Routing exam. The concepts and commands covered on the exam are not secrets locked in some vault the information is available in many places and forms, including this book. So, although the exam is difficult, passing is certainly attainable with study.
Goals of This Book
The goals for this book became somewhat obvious to me after considering the exam itself, as well as Cisco's exam philosophy. The first goal came straight from Cisco, who asked that I write a book that not only helps you pass the exam, but that also ensures that you really understand the concepts and implementation details. The second goal of this book is that the content should be the most comprehensive coverage of Routing 2.0 exam-related topics available, without too much coverage of topics not on the exam. The third and ultimate goal is to get you from where you are today to the point that you can confidently pass the Routing 2.0 exam. Therefore, all this book's features, which are outlined in this chapter, are geared toward helping you discover the IP routing topics that are on the Routing exam, where you have a knowledge deficiency in these topics, and what you need to know to master these topics...
CCNP Support Exam Certification Guide
Chapter 1: Support Resources for TroubleshootingNetwork Management Systems
Computer networks have become complex for several reasons. There are many different makes and models of devices. Most networks deploy a variety of protocols and applications. Several local-area, wide-area, and remote access technologies and techniques have been invented. Making all of these components work together reliably with maximum availability is not a trivial task. Network management systems are tools to help understand, monitor, troubleshoot, modify, scale, and secure networks.
The five key functional areas of network management, as per the International Organization for Standardization (ISO) definition, are
Fault management, a major troubleshooting topic, is about discovering abnormal behavior before or shortly after it happens. Once a problem is detected, take the following sequence of actions:
1 Determine the problem area.
2 Isolate the problem area and take advantage of alternate paths (complex networks usually have fault-tolerance and/or redundancy built in).
3 Attempt to minimize the impact of the failure(s).
4 Discover the specific device(s) causing the fault(s).
5 Identify the component/subsystem that is malfunctioning and needs to be replaced or reconfigured.
6 Implement the solution and pave the way for restoring the normal network operation.
NOToblem is especially common with the 3Com Impact adapter running firmware version 2.02. If you think the second telephone number might be the problem, try reconfiguring your adapter to use only one of your ISDN numbers.
Drivers are not supported in Windows 98.
ISDN drivers from the ISDN version 1.0 Accelerator Pack are not supported in Windows 98. Contact your ISDN adapterc; The systematic troubleshooting methodology that guides you from problem definition through discovery of the problem and implementing the solution is discussed in Chapter 2, "Understanding Troubleshooting Methods."
The remainder of this section covers the following:
CiscoWorks is Cisco Systems' network management software. This software is based on Simple Network Management Protocol and it is for managing networks with one integrated platform. CiscoWorks provides services that have both operations and management value. Network managers can monitor routers (down to port activity), observe traffic patterns, modify configurations, observe and report inventory, capture data (for accounting purposes), and observe security settings all from their one central station. Some of the main components of CiscoWorks (classic-that is, prior to CiscoWorks 2000) are
There are other software applications, such as CiscoView, bundled with CiscoWorks. CiscoView is also available as a standalone product and can be integrated with other network management platforms such as SunNet Manager, HP OpenView, and IBM NetView. CiscoView is a GUI software that provides real-time device level monitoring (providing status and statistics information), fault management, and troubleshooting.
Another valuable network management tool is Cisco Resource Manager (CRM). CRM is web-based and among its components there are four essential applications: Inventory Manager, Availability Manager, Syslog Analyzer, and Software Image Manager. CRM complements CiscoView and other parts of CiscoWorks network management software.
CiscoWorks for Switched Internetworks Software
CWSI Campus is a suite of network management applications that together provide remote monitoring, configuration, and management of switched internetworks. The following are included in the CWSI Campus package:
For a description of these components, refer to www.cisco.com/univercd/cc/td/doc/ product/rtrmgmt/sw ntman/cwsimain/cwsi2/cwsiug2/gsg/gsin.htm at the Cisco Documentation site. CWSI can be integrated with other SNMP-based network management systems, such as SunNet Manager, HP OpenView, and IBM NetView. Protocols such as SNMP, Cisco Discovery Protocol (CDP), VLAN Trunking Protocol (VTP), and RMON form the foundation of the CWSI application suite. One of the valuable features of CWSI Campus is Network Map. This application provides a map of the physical devices and links in your network,which it automatically discovers, provided that there is a Cisco seed device present. You can then locate specific devices in the network and view how they are linked together. Network Map can also display the network virtual topology (virtual LAN configuration) in relation to the physical topology.
TrafficDirector Remote Monitoring Software
The TrafficDirector software is an application in the CWSI Campus suite of network management applications. This software allows you to monitor traffic (on network segments) leading to the diagnosis of any abnormalities. TrafficDirector obtains traffic information from embedded RMON agents (of Catalyst switches) and standalone Cisco SwitchProbe products. With this information, TrafficDirector can inform you of collisions, errors, utilization, and broadcast rates on a port (or port group) basis. You can also set up TrafficDirector to receive threshold-based traps from Catalyst switches. Hence, TrafficDirector is considered an excellent fault and performance management tool. Furthermore, since you can capture remote packets and profile network traffic on a multilayer basis, TrafficDirector is also considered a remote monitoring and traffic analysis tool.
Simulation and Modeling Tools
As the name implies, simulation and modeling tools are meant to allow you to put a network together (using the software) and see how it performs. You can use these tools to design a brand new network or to see how an existing network will perform if you modify it, expand it, or put traffic stress on it. Simulation tools allow you to select networking devices and interconnect them with a variety of serial, LAN media, dialup, and WAN services. You can configure the selected devices line by line or assign preexisting real configuration files to them, and analyze the simulated network's operation. If you have a network analyzer that can export captured data into a format that you can feed to your simulation software, you can then see how the simulated network behaves or reacts to the real traffic.
A useful function of simulation tools is reporting on throughput, utilization, response time, error rate, dropped packets, and other performance-related data during the simulation period. This capability is valuable for evaluating small or significant proposed changes before committing to them and, hence, can prevent financial and operational disasters. Additionally, the impact of failed segments and/or devices can be analyzed and used to evaluate options such as implementing fault tolerant devices, redundant links, or high capacity/reliable technologies. Cisco Netsys is a product that offers such services. The demonstration version of Netsys (installable on Windows NT platforms, for example) provides a video presentation about the capabilities of this software; furthermore, it provides you with a subset of the full version's capabilities for your evaluation.
Cisco Connection Online (CCO)
CCO provides a suite of interactive web-based services that offer open access to Cisco's information, systems, resources, and personnel-24 hours a day, 7 days a week, from anywhere in the world. Figure 1-4 displays CCO's home page (www.cisco.com).
The online/interactive services offered by Cisco over the Internet have evolved and grown over time. Today you have access to a wealth of technical knowledge, tips, bug information, support services, and other valuable resources all from one place. CCO is not only about obtaining information; you may, for example, access the online price list on Cisco products, place orders, download Cisco Internetwork Operating System (IOS) software images, or receive technical assistance and many other services. There are two levels of access available: guest access and registered access. Table 1-1 shows the benefits of each and how they relate to troubleshooting...
Cisco CCNP Switching Exam Certification Guide
Chapter 2: Campus Network Design Models...Shared Network Model
Campus networks have traditionally been constructed of a single LAN for all users to connect to and use. All devices on the LAN were forced to share the available bandwidth. LAN media such as Ethernet and Token Ring both have distance limitations, as well as limitations on the number of devices that could be connected to a single LAN.
Network availability and performance both declined as the number of connected devices increased. For example, an Ethernet LAN required all devices to share the available 10-Mbps half-duplex bandwidth. Ethernet also used the carrier sense multiple access collision detect (CSMA/CD) scheme to determine when a device could transmit data on the shared LAN. If two or more devices tried to transmit at the same time, network collisions occurred and all devices had to become silent and wait to retransmit their data. This type of LAN is a collision domain because all devices were susceptible to collisions. Token Ring LANs are not susceptible to collisions because they are deterministic and allow stations to transmit only when they receive a "token" that passes around the ring.
One solution used to relieve network congestion was to segment or divide a LAN into discrete collision domains. This solution used transparent bridges, which only forwarded Layer 2 data frames to the network segment where the destination address was located. Bridges enabled the number of devices on a segment to be reduced, lessened the probability of collisions on segments, and increased the physical distance limitations by acting as a repeater.
Bridges normally forward frames to the LAN segment where the destination address is located. However, frames containing the broadcast MAC address (ff:ff:ff:ff:ff:ff) must be flooded out to all connected segments. Broadcast frames are usually associated with requests for information or services, including network service announcements. IP uses broadcasts for Address Resolution Protocol (ARP) requests to ask what MAC address is associated with a particular IP address. Other examples of broadcast frames include IPX Get Nearest Server (GNS) requests, Service Advertising Protocol (SAP) announcements, Routing Information Protocol (RIP-both IP and IPX) advertisements, and NetBIOS name requests. A broadcast domain is a group of network segments where a broadcast is flooded.
Multicast traffic is traffic that is destined for a specific set or group of users, regardless of their location on the campus network. Multicast frames must be flooded to all segments because they are a form of broadcast. Although end users must join a multicast group to enable their applications to process and receive the multicast data, a bridge must flood the traffic to all segments because it doesn't know which stations are members of the multicast group. Multicast frames will use shared bandwidth on a segment, but will not force the use of CPU resources on every connected device. Only the CPUs that are registered as multicast group members will actually process those frames. Some multicast traffic is sporadic, as in the case of various routing protocol advertisements, while other traffic such as Cisco IP/TV multicast video can consume most or all the network resources with a steady stream of real-time data.
Broadcast traffic presents a two-fold performance problem on a bridged LAN because all broadcast frames flood all bridged network segments. First, as a network grows, the broadcast traffic can grow in proportion and monopolize the available bandwidth. Secondly, all end-user stations must listen to, decode, and process every broadcast frame. This function is performed by the CPU, which must look further into the frame to see with which upper layer protocol the broadcast is associated. While today's CPUs are robust and might not show a noticeable degradation from processing broadcasts, forcing unnecessary broadcast loads upon every end user is not wise.
LAN Segmentation Model
Referred to as network segmentation, localizing the traffic and effectively reducing the number of stations on a segment is necessary to prevent collisions and broadcasts from reducing a network segment's performance. By reducing the number of stations, the probability of a collision decreases because fewer stations can be transmitting at a given time. For broadcast containment, the idea is to provide a barrier at the edge of a LAN segment so that broadcasts cannot pass or be forwarded on outward. The network designer can provide segmentation by using either a router or a switch.
Routers can be used to connect the smaller subnetworks and either route Layer 3 packets or bridge Layer 2 packets. The effect of collisions can be improved with fewer stations on each segment. A router cannot propagate a collision condition from one segment to another. As well, broadcasts are not forwarded to other subnets by default, unless bridging (or some other specialized feature) is enabled on the router. Figure 2-2 shows an example of how a campus network can be segmented physically by a router. Although broadcasts are contained, the router becomes a potential bottleneck because it must process and route every packet leaving each subnet.
Another option is to replace shared LAN segments with switches. Switches offer greater performance with dedicated bandwidth on each port. A switch can be thought of as a very fast multiport bridge. Each switch port becomes a separate collision domain, and will not propagate collisions to any other port. However, broadcast and multicast frames are flooded out all switch ports unless more advanced switch features are invoked. Multicast switch features are covered in Chapter 11, "Configuring Multicast Networks."
To contain broadcasts and segment a broadcast domain, implement virtual LANs (VLANs) within the switched network. A switch can logically divide its ports into isolated segments. VLANs are groups of switch ports (and the end devices they are connected to) that communicate as if attached to a single shared-media LAN segment. By definition, a VLAN becomes a single broadcast domain. VLAN devices don't have to be physically located on the same switch or in the same building, as long as the VLAN itself is somehow connected between switches end-to-end. Figure 2-3 shows how a network can be segmented into three broadcast and collision domains using three VLANs on a switch. Note that stations on a VLAN cannot communicate with stations on another VLAN in the figure-the VLANs are truly isolated.
By default, all ports on a switch are assigned to a single VLAN. With additional configuration, a switch can assign its ports to many specific VLANs. Each VLAN, although present on the same switch, is effectively separated from other VLANs. Frames will not be forwarded from one VLAN to another. To communicate between VLANs, a router (or Layer 3 device) is required as illustrated by Figure 2-4.
Ports on the switch have been grouped and assigned to three VLANs. A port from each VLAN also connects to the router. The router then forwards packets between VLANs through these ports. Note that each switch link in the figure supports two VLANs. Because a switch link can be configured only for one VLAN, it has been configured for trunking, or carrying multiple VLANs. (Trunking is discussed in Chapter 4, "VLANs and Trunking.")
To gain the most benefit from routed approaches and VLAN approaches, most campus networks are now built with both LAN switches and routers. Again, the Layer 2 switches are generally placed where the small broadcast domains are located, linked by routers that provide Layer 3 functionality. In this manner, broadcast traffic can be controlled or limited. Users also can be organized and given access to common workgroups, while traffic between workgroups can be interconnected and secured. Figure 2-5 illustrates the structure of a typical routed and switched campus network.
Network Traffic Models
To design and build a successful campus network, you must gain a thorough understanding of the traffic generated by applications in use, plus the traffic flow to and from the user communities. All devices on the network will produce data to be transported across the network. Each device could involve many applications that generate data with differing patterns and loads.
Applications such as electronic mail, word processing, printing, file transfer, and most web browsers bring about data traffic patterns that are predictable from source to destination. However, newer applications such as videoconferencing, TV or video broadcasts, and IP telephony have a more dynamic user base, which makes traffic patterns difficult to predict or model.
Traditionally, users with similar applications or needs have been placed in common workgroups, along with the servers they access most often. Whether these workgroups are logical (VLAN) or physical networks, the idea is to keep the majority of traffic between clients and servers limited to the local network segment. In the case of the switched LANs connected by routers mentioned earlier, both clients and servers would be connected to a Layer 2 switch in the proximity of the workgroup. This connection provides good performance while minimizing the traffic load on the routed network backbone.
This concept of network traffic patterns is known as the 80/20 rule. In a properly designed campus network, 80 percent of the traffic on a given network segment is local (switched). No more than 20 percent of the traffic is expected to move across the network backbone (routed).
If the backbone becomes congested, the network administrator will realize that the 80/20 rule is no longer being met. What recourses are available to improve network performance again? Upgrading the campus backbone is not a desirable option, due to the expense and complexity. The whole idea behind the 80/20 rule is to keep traffic off the backbone in the first place. Instead, the administrator can implement the following solutions:
Needless to say, conforming modern campus networks to the 80/20 rule has become difficult for the network administrator. Newer applications still use the client/server model, but server portions have been centralized in most enterprises. For example, databases, Internet and intranet technologies, and electronic mail are all available from centralized servers. Not only do these applications involve larger amounts of data, they also require a greater percentage of traffic to cross a network backbone to reach common destinations-quite a departure from the 80/20 rule.
This new model of campus traffic has become known as the 20/80 rule. Now, only 20 percent of the traffic is local to the workgroup, while at least 80 percent of the traffic is expected to travel off the local network and across the backbone.
This shift in traffic patterns puts a greater burden on the Layer 3 technology of the campus backbone. Now, because traffic from anywhere on the network can be destined for any other part of the network, the Layer 3 performance ideally should match the Layer 2 performance...