CCNP Switching Exam Certification Guide

CCNP Switching Exam Certification Guide

by David Hucaby, Tim Boyles
The official study guide for CCNP and CCDP Switching Exam #640-504

Coverage of the CCNP/CCDP Switching exam topics enables you to identify and fill your knowledge gaps before the exam date. You will learn how to:

  • Design, build, and maintain high-speed, multilayer switched networks running Fast and Gigabit Ethernet
  • Define common workgroups


The official study guide for CCNP and CCDP Switching Exam #640-504

Coverage of the CCNP/CCDP Switching exam topics enables you to identify and fill your knowledge gaps before the exam date. You will learn how to:

  • Design, build, and maintain high-speed, multilayer switched networks running Fast and Gigabit Ethernet
  • Define common workgroups and configure and manage Virtual LANs with VTP
  • Utilize redundant switch links to increase campus network reliability
  • Understand ATM and use LAN Emulation (LANE) technology for trunking
  • Configure Catalyst switches and Cisco routers to enable interVLAN routing, providing complete connectivity across the switched network
  • Apply HSRP in the campus environment to provide load sharing and backup capabilities
  • Understand and configure basic multicast networks, implementing services at each layer of the network to enable access to multicast groups
  • Control network traffic with access policies

CCNP Switching Exam Certification Guide is a comprehensive study tool for the CCNP/CCDP Switching Exam #640-504. This exam evaluates your ability to build campus networks using multilayer switching technologies and to manage campus network traffic. This book covers all the major topics on the Switching Exam, enabling you to master the concepts and technologies upon which you will be tested, including switched Ethernet, trunking, multicasting, multilayer switching, VLANs, ATM, LANE, interVLAN routing, HSRP, network traffic control, and monitoring and troubleshooting techniques.

Each chapter of CCNP Switching Exam Certification Guide focuses your study and tests your knowledge of the subjects throughspecially designed assessment and study features. "Do I Know This Already?" quizzes assess your knowledge and help you decide how much time you need to spend on each section within a chapter. The well-organized Foundation Topics sections detail all of the exam topics you need to master. Each chapter includes a Foundation Summary section highlighting essential concepts for quick reference. Challenging chapter-ending review questions and exercises test your knowledge of the subject matter, reinforce key concepts, and provide you with the opportunity to apply what you have learned in the chapter. In addition, a final chapter of scenarios pulls together concepts from all of the chapters to ensure you can apply your knowledge in a real-world environment. Finally, the companion CD-ROM's robust testing engine enables you to take practice exams that mimic the real testing environment, focus on particular topic areas, randomize answers for reusability, track your progress, and refer to electronic text for review.

CCNP Switching Exam Certification Guide is part of a recommended study program from Cisco Systems that includes training courses and materials from Cisco's Internet Learning Solutions Group, hands-on experience, and Coursebooks and exam guides from Cisco Press. With experience and training under your belt, this book enables you to retain and master the multilayer switching knowledge vital for attaining CCNP or CCDP certification and succeeding in your daily job.

Companion CD-ROM
This companion CD-ROM contains a test bank with over 200 practice questions.

Editorial Reviews

A study guide for taking the Cisco-certified network professional (CCNP) switching exam #640-504. Quizzes at the beginning of each chapter assess areas of strength and weakness, and direct the reader to the appropriate sections for study. Topics include campus network design models, VLANs and trunking, redundant switch links, multilayer switching, configuring multicast networks, and the hot standby router protocol. The CD-ROM contains an exam simulation for practice. Annotation c. Book News, Inc., Portland, OR (

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Cisco Press
Publication date:
CCNP/Ccdp Certification and Training Series
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Read an Excerpt

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 segmentwhere 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:

  • Reassign existing resources to bring the users and servers closer together.
  • Move applications and files to a different server to stay within a workgroup.
  • Move users logically (assigned to new VLANs) or physically to stay near their workgroups.
  • Add more servers, which can bring resources closer to the respective workgroups.

    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...

  • Meet the Author

    Tim Boyles, CCNP, also is a senior network systems consultant with International Network Services, where he helps numerous customers with planning, configuration, and troubleshooting of multiprotocol networks. His areas of specialty include Cisco Catalyst switches, Cisco routers, LAN hardware, network protocols, and network operating systems.

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