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About the Author

David Hucaby, CCIE No. 4594, is a lead network engineer for the University of Kentucky, where he works with healthcare networks based on the Cisco Catalyst, ASA, FWSM, and VPN product lines. David has a bachelor of science degree and master of science degree in electrical engineering from the University of Kentucky. He is the author of three previous books for Cisco Press, including Cisco ASA and PIX Firewall Handbook, Cisco Field Manual Router Configuration, and Cisco Field Manual Catalyst...

Access Point Operation

An AP's primary function is to bridge wireless data from the air to a normal wired network. An AP can accept connections from a number of wireless clients so that they become members of the LAN, as if the same clients were using wired connections. An AP can also act as a bridge to form a single wireless link from one LAN to another over a long distance. In that case, an AP is needed on each end of the wireless link. AP-to-AP or line-of-sight links are commonly used for connectivity between...

Acknowledgments

It has been my great pleasure to work on another Cisco Press project. I enjoy the networking field very much, and technical writing even more. And more than that, I'm thankful for the joy and inner peace that Jesus Christ gives, making everything more abundant. Technical writing may be hard work, but I'm finding that it's also quite fun because I'm working with very good friends. I can't say enough good things about Chris Cleveland. Somehow Chris is able to handle many book projects all at...

Avoiding Collisions in a WLAN

When two or more wireless stations transmit at the same time, their signals become mixed. Receiving stations can see the result only as garbled data, noise, or errors. No clear-cut way exists to determine whether a collision has occurred. Even the transmitting stations won't realize it because their receivers must be turned off while they are transmitting. As a basic feedback mechanism, whenever a wireless station transmits a frame, the receiving wireless station must send an acknowledgement...

Backbone Fast Redundant Backbone Paths

In the network backbone, or core layer, a different method is used to shorten STP convergence. BackboneFast works by having a switch actively determine whether alternative paths exist to the Root Bridge, in case the switch detects an indirect link failure. Indirect link failures occur when a link that is not directly connected to a switch fails. A switch detects an indirect link failure when it receives inferior BPDUs from its designated bridge on either its Root Port or a blocked port....

Basic RF Operation

Radio frequency (RF) communication begins with an oscillating signal transmitted from one device to be received on one or more other devices. This oscillating signal is based around a constant, known frequency. Because the transmitter uses a set frequency, a receiver can tune to the same frequency and receive the same signal. You have probably had this experience by tuning a radio receiver in a car. Basically, the transmitting station has a transmitter that generates the RF signal, an antenna,...

BPDUs in RSTP

In 802.1D, BPDUs basically originate from the Root Bridge and are relayed by all switches down through the tree. Because of this propagation of BPDUs, 802.1D convergence must wait for steady-state conditions before proceeding. RSTP uses the 802.1D BPDU format for backward compatibility. However, some previously unused bits in the Message Type field are used. The sending switch port identifies itself by its RSTP role and state. The BPDU version also is set to 2 to distinguish RSTP BPDUs from...

Bridging Loops

Recall that a Layer 2 switch mimics the function of a transparent bridge. A transparent bridge must offer segmentation between two networks while remaining transparent to all the end devices connected to it. For the purpose of this discussion, consider a two-port Ethernet switch and its similarities to a two-port transparent bridge. A transparent bridge (and the Ethernet switch) must operate as follows The bridge has no initial knowledge of any end device's location therefore, the bridge must...

Bundling Ports with Ether Channel

EtherChannel bundles can consist of up to eight physical ports of the same Ethernet media type and speed. Some configuration restrictions exist to ensure that only similarly configured links are bundled. Generally, all bundled ports first must belong to the same VLAN. If used as a trunk, bundled ports must be in trunking mode, have the same native VLAN, and pass the same set of VLANs. Each of the ports should have the same speed and duplex settings before being bundled. Bundled ports also must...

Can I Use Layer 2 Distribution Switches

This chapter covers the best practice design that places Layer 3 switches at both the core and distribution layers. What would happen if you could not afford Layer 3 switches at the distribution layer Figure 2-5 shows a dual-core campus network with Layer 2 distribution switches. Notice how each access VLAN extends not only throughout the switch block but also into the core. This is because the VLAN terminates at a Layer 3 boundary present only in the core. As an example, VLAN A's propagation...

Command Syntax Conventions

The conventions used to present command syntax in this book are the same conventions used in the IOS Command Reference. The Command Reference describes these conventions as follows Boldface indicates commands and keywords that are entered literally as shown. In actual configuration examples and output (not general command syntax), boldface indicates commands that are manually input by the user (such as a show command). Italics indicate arguments for which you supply actual values. Vertical bars...

Configuring a LACP Ether Channel

To configure switch ports for LACP negotiation, use the following commands Switch(config) lacp system-priority priority Switch(config) interface type mod num Switch(config-if) channel-protocol lacp Switch(config-if) channel-group number mode on I passive I active Switch(config-if) lacp port-priority priority First, the switch should have its LACP system priority defined (1 to 65,535 default 32,768). If desired, one switch should be assigned a lower system priority than the other so that it can...

Contents

Part I Overview and Design of a Campus Network 3 Do I Know This Already Quiz 5 Switching Functionality 9 Layer 2 Switching 10 Layer 3 Routing 11 Layer 3 Switching 11 Layer 4 Switching 12 Multilayer Switching 12 Campus Network Models 13 Shared Network Model 13 LAN Segmentation Model 15 Network Traffic Models 18 Predictable Network Model 19 Hierarchical Network Design 20 Access Layer 21 Distribution Layer 21 Core Layer 22 Do I Know This Already Quiz 27 Modular Network Design 31 Switch Block 32...

Contents at a Glance

Overview and Design of a Campus Network Traditional Spanning Tree Protocol 181 Protecting the Spanning Tree Protocol Topology 243 Router, Supervisor, and Power Redundancy Chapter 17 Wireless LAN Overview 431 Chapter 18 Wireless Architecture and Design 471 Chapter 19 Cisco Unified Wireless Network 497 Part VI Scenarios for Final Preparation 533 Chapter 20 Scenarios for Final Preparation 535 Appendix A Answers to Chapter Do I Know This Already Quizzes and Q& A Sections 555

Core Layer

A campus network's core layer provides connectivity of all distribution-layer devices. The core, sometimes referred to as the backbone, must be capable of switching traffic as efficiently as possible. Core devices, sometimes called campus backbone switches, should have the following attributes Very high throughput at Layer 2 or Layer 3 No costly or unnecessary packet manipulations (access lists, packet filtering) Redundancy and resilience for high availability Devices in a campus network's core...

Deploying VLANs

To implement VLANs, you must consider the number of VLANs you need and how best to place them. As usual, the number of VLANs depends on traffic patterns, application types, segmentation of common workgroups, and network-management requirements. An important factor to consider is the relationship between VLANs and the IP addressing schemes used. Cisco recommends a one-to-one correspondence between VLANs and IP subnets. This recommendation means that if a subnet with a 24-bit mask (255.255.255.0)...

Distribution Layer

The distribution layer provides interconnection between the campus network's access and core layers. Devices in this layer, sometimes called building distribution switches, should have the following capabilities Aggregation of multiple access-layer devices High Layer 3 throughput for packet handling Security and policy-based connectivity functions through access lists or packet filters Scalable and resilient high-speed links to the core and access layers In the distribution layer, uplinks from...

Do I Know This Already

Put the following Ethernet standards in order of increasing bandwidth 2. What benefits does switched Ethernet have over shared Ethernet Answer Switched Ethernet ports receive dedicated bandwidth, have a reduced collision domain, and show increased performance because of segmentation or fewer users per port. 3. When a 10 100 Ethernet link is autonegotiating, which will be chosen if both stations can support the same capabilities 10BASE-T full duplex, 100BASE-TX half duplex, or 100BASE-TX full...

Do I Know This Already Quiz

The purpose of the Do I Know This Already quiz is to help you decide whether you need to read the entire chapter. If you already intend to read the entire chapter, you do not necessarily need to answer these questions now. The 12-question quiz, derived from the major sections in the Foundation Topics portion of the chapter, helps you determine how to spend your limited study time. Table 8-1 outlines the major topics discussed in this chapter and the Do I Know This Already quiz questions that...

Dynamic Trunking Protocol

You manually can configure trunk links on Catalyst switches for either ISL or 802.1Q mode. In addition, Cisco has implemented a proprietary, point-to-point protocol called Dynamic Trunking Protocol (DTP) that negotiates a common trunking mode between two switches. The negotiation covers the encapsulation (ISL or 802.1Q) and whether the link becomes a trunk at all. This allows trunk links to be used without a great deal of manual configuration or administration. The use of DTP is explained in...

Electing a Root Bridge

For all switches in a network to agree on a loop-free topology, a common frame of reference must exist to use as a guide. This reference point is called the Root Bridge. (The term bridge continues to be used even in a switched environment because STP was developed for use in bridges. Therefore, when you see bridge, think switch.) An election process among all connected switches chooses the Root Bridge. Each switch has a unique Bridge ID that identifies it to other switches. The Bridge ID is an...

Electing Designated Ports

By now, you should begin to see the process unfolding A starting or reference point has been identified, and each switch connects itself toward the reference point with the single link that has the best path. A tree structure is beginning to emerge, but links have only been identified at this point. All links still are connected and could be active, leaving bridging loops. To remove the possibility of bridging loops, STP makes a final computation to identify one Designated Port on each network...

Electing Root Ports

Now that a reference point has been nominated and elected for the entire switched network, each nonroot switch must figure out where it is in relation to the Root Bridge. This action can be performed by selecting only one Root Port on each nonroot switch. The Root Port always points toward the current Root Bridge. STP uses the concept of cost to determine many things. Selecting a Root Port involves evaluating the Root Path Cost. This value is the cumulative cost of all the links leading to the...

Ether Channel Configuration

For each EtherChannel on a switch, you must choose the EtherChannel negotiation protocol and assign individual switch ports to the EtherChannel. Both PAgP- and LACP-negotiated EtherChannels are described in the following sections. You also can configure an EtherChannel to use the on mode, which unconditionally bundles the links. In this case, neither PAgP nor LACP packets are sent or received. As ports are configured to be members of an EtherChannel, the switch automatically creates a logical...

Ethernet Concepts

This section reviews the varieties of Ethernet and their application in a campus network. Recall how the bandwidth requirements for each network segment are determined by the types of applications in use, the traffic flows within the network, and the size of the user community served. Ethernet scales to support increasing bandwidths and should be chosen to match the need at each point in the campus network. As network bandwidth requirements grow, you can scale the links between access,...

Evaluating an Existing Network

If you are building an enterprise network from scratch, you might find that it is fairly straightforward to build it in a hierarchical fashion. After all, you can begin with switches in the core layer and fan out into lower layers to meet the users, server farms, and service providers. In the real world, you might be more likely to find existing networks that need an overhaul to match the hierarchical model. Hopefully, if you are redesigning your own network, you already know its topology and...

Forwarding Information Base

The Layer 3 engine (essentially a router) maintains routing information, whether from static routes or dynamic routing protocols. Basically, the routing table is reformatted into an ordered list with the most specific route first, for each IP destination subnet in the table. The new format is called a Forwarding Information Base (FIB) and contains routing or forwarding information that the network prefix can reference. In other words, a route to 10.1.0.0 16 might be contained in the FIB along...

Foundation Summary

The Foundation Summary is a collection of information that provides a convenient review of many key concepts in this chapter. If you are already comfortable with the topics in this chapter, this summary can help you recall a few details. If you just read this chapter, this review should help solidify some key facts. If you are doing your final preparation before the exam, this information will hopefully be a convenient way to review the day before the exam. Table 17-5 Quick Comparison of...

Hierarchical Network Design

You can structure the campus network so that each of the three types of traffic flows or services outlined in Table 1-3 is best supported. Cisco has refined a hierarchical approach to network design that enables network designers to logically create a network by defining and using layers of devices. The resulting network is efficient, intelligent, scalable, and easily managed. The hierarchical model breaks a campus network into three distinct layers, as illustrated in Figure 1-5. Figure 1-5...

How to Use This Book for Study

Retention and recall are the two features of human memory most closely related to performance on tests. This exam-preparation guide focuses on increasing both retention and recall of the topics on the exam. The other human characteristic involved in successfully passing the exam is intelligence this book does not address that issue Adult retention is typically less than that of children. For example, it is common for 4-year-olds to pick up basic language skills in a new country faster than...

Inter Controller Roaming

In some cases, a client might roam from one controller to another. For example, a large wireless network might consist of too many LAPs to be supported by a single WLC. The LAPs could also be distributed over several controllers for load balancing or redundancy purposes. In Figure 19-10, a wireless client is using an association with WLC1 through API. This is similar to Figure 19-8, but now each of the adjacent LAP cells belongs to a different WLC. All the client's traffic passes through the...

Intra Controller Roaming

In Figure 19-8, a wireless client has an active wireless association at location A. The association is with WLC1 through AP1. As you might expect, all traffic to and from the client passes through the LWAPP tunnel between AP1 and WLC1. Figure 19-8 A Wireless Client in an LAP Cell Before Roaming Figure 19-8 A Wireless Client in an LAP Cell Before Roaming The client begins moving in Figure 19-9 and roams into the area covered by AP2. For this example, notice two things The cells provided by AP1...

Layer 2 QoS Classification

Layer 2 frames themselves have no mechanism to indicate the priority or importance of their contents. One frame looks just as important as another. Therefore, a Layer 2 switch can forward frames only according to a best-effort delivery. When frames are carried from switch to switch, however, an opportunity for classification occurs. Recall that a trunk is used to carry frames from multiple VLANs between switches. The trunk does this by encapsulating the frames and adding a tag indicating the...

Lightweight AP Operation

The lightweight AP is designed to be a zero-touch configuration. The LAP must find a WLC and obtain all of its configuration parameters, so you never have to actually configure it through its console port or over the network. The following sequence of steps detail the bootstrap process that an LAP must complete before it becomes active Step 1 The LAP obtains an IP address from a DHCP server. Step 2 The LAP learns the IP addresses of any available WLCs. Step 3 The LAP sends a join request to the...

Multiple Spanning Tree Protocol

Chapter 8 covered two flavors of spanning-tree implementations IEEE 802.1Q and PVST+ both based on the 802.1D STP. These also represent the two extremes of STP operation in a network 802.1Q Only a single instance of STP is used for all VLANs. If there are 500 VLANs, only one instance of STP will be running. This is called the Common Spanning Tree (CST) and operates over the trunk's native VLAN. PVST+ One instance of STP is used for each active VLAN in the network. If there are 500 VLANs, 500...

Objectives and Methods

The most important and somewhat obvious objective of this book is to help you pass the Cisco BCMSN exam (642-812). In fact, if the primary objective of this book were different, the book's title would be misleading however, the methods used in this book to help you pass the BCMSN exam are designed to also make you much more knowledgeable about how to do your job. Although this book and the accompanying CD-ROM have many sample test questions, the method in which they are used is not to simply...

Packet Forwarding Review

When a host must communicate with a device on its local subnet, it can generate an Address Resolution Protocol (ARP) request, wait for the ARP reply, and exchange packets directly. However, if the far end is located on a different subnet, the host must rely on an intermediate system (a router, for example) to relay packets to and from that subnet. A host identifies its nearest router, also known as the default gateway or next hop, by its IP address. If the host understands something about...

Overview and Design of a Campus Network

Chapter 1 Campus Network Overview Chapter 2 Modular Network Design This chapter covers the following topics that you need to master for the CCNP BCMSN exam Switching Functionality This section covers the use of switches in the OSI model layers. You learn about the functions and application of routing and switching in Layers 2, 3, and 4, along with the concept of multilayer switching. Campus Network Models This section presents the concept of a campus network, and describes the traditional...

Building a Campus Network

Chapter 4 Switch Port Configuration Chapter 6 VLAN Trunking Protocol Chapter 7 Aggregating Switch Links Chapter 8 Traditional Spanning Tree Protocol Chapter 9 Spanning Tree Configuration Chapter 10 Protecting the Spanning Tree Protocol Topology Chapter 11 Advanced Spanning Tree Protocol This chapter covers the following topics that you need to master for the CCNP BCMSN exam Layer 2 Switch Operation This section describes the functionality of a switch that forwards Ethernet frames. Multilayer...

Layer 3 Switching

Chapter 13 Router, Supervisor, and Power Redundancy This chapter covers the following topics that you need to master for the CCNP BCMSN exam InterVLAN Routing This section discusses how you can use a routing function with a switch to forward packets between VLANs. Multilayer Switching with CEF This section discusses Cisco Express Forwarding (CEF) and how it is implemented on Catalyst switches. CEF forwards or routes packets in hardware at a high throughput. Troubleshooting Multilayer Switching...

Campus Network Services

Chapter 14 IP Telephony Chapter 15 Securing Switch Access Chapter 16 Securing with VLANs This chapter covers the following topics that you need to master for the CCNP BCMSN exam Power over Ethernet This section discusses how a Catalyst switch can provide power to operate devices such as Cisco IP Phones. Voice VLANs This section explains how voice traffic can be carried over the links between an IP Phone and a Catalyst switch. Voice QoS This section provides an overview of the mechanisms that...

Wireless LANs

Chapter 17 Wireless LAN Overview Chapter 18 Wireless Architecture and Design Chapter 19 Cisco Unified Wireless Network This chapter covers the following topics that you need to master for the CCNP BCMSN exam Wireless LAN Basics This section discusses wireless networks as they compare to wired Ethernet networks. WLAN Building Blocks This section covers wireless service sets in addition to wireless access points and their coverage areas. An Introduction to Wireless LAN RF Wireless networks use...

Port Aggregation Protocol

To provide automatic EtherChannel configuration and negotiation between switches, Cisco developed the Port Aggregation Protocol. PAgP packets are exchanged between switches over EtherChannel-capable ports. Neighbors are identified and port group capabilities are learned and compared with local switch capabilities. Ports that have the same neighbor device ID and port group capability are bundled together as a bidirectional, point-to-point EtherChannel link. PAgP forms an EtherChannel only on...

Port Fast Access Layer Nodes

An end-user workstation is usually connected to a switch port in the access layer. If the workstation is powered off and then turned on, the switch will sense that the port link status has gone down and back up. The port will not be in a usable state until STP cycles from the Blocking state to the Forwarding state. With the default STP timers, this transition takes at least 30 seconds (15 seconds for Listening to Learning, and 15 seconds for Learning to Forwarding). Therefore, the workstation...

Predictable Network Model

Ideally, you should design a network with a predictable behavior in mind to offer low maintenance and high availability. For example, a campus network needs to recover from failures and topology changes quickly and in a predetermined manner. You should scale the network to easily support future expansions and upgrades. With a wide variety of multiprotocol and multicast traffic, the network should be capable of supporting the 20 80 rule from a traffic standpoint. In other words, design the...

Qa

The questions and scenarios in this book are more difficult than what you should experience on the actual exam. The questions do not attempt to cover more breadth or depth than the exam however, they are designed to make sure that you know the answer. Rather than allowing you to derive the answers from clues hidden inside the questions themselves, the questions challenge your understanding and recall of the subject. Hopefully, these questions will help limit the number of exam questions on...

R

Radius of Fresnel zones, calculating, 451-452 ranges of ports, selecting, 95 REAP (Cisco Remote Edge Access Point), 509 reception of RF signals, factors affecting absorption, 448-449 diffraction, 449-450 Fresnel zones, 450-452 reflection, 447-448 refraction, 448 scattering, 449 recovering from switch port error conditions, 99 redirect timer (AVFs), 332 redundancy, 313 gateway addresses, 317 HSRP, 318 of Catalyst switches non-stop forwarding, 343 power supplies, 343-345 supervisor...

Rapid PerVLAN Spanning Tree Protocol

Chapter 8, Traditional Spanning Tree Protocol, described PVST+ as the default STP mode on Catalyst switches. In PVST+, one spanning tree instance is created and used for each active VLAN that is defined on the switch. Each STP instance behaves according to the traditional 802.1D STP rules. You can improve the efficiency of each STP instance by configuring a switch to begin using RSTP instead. This means that each VLAN will have its own independent instance of RSTP running on the switch. This...

Router Redundancy in Multilayer Switching

Multilayer switches can act as IP gateways for connected hosts by providing gateway addresses at VLAN SVIs and Layer 3 physical interfaces. These switches can also participate in routing protocols, just as traditional routers do. For high availability, multilayer switches should offer a means of preventing one switch (gateway) failure from isolating an entire VLAN. This chapter discusses several approaches to providing router redundancy, including the following Hot Standby Router Protocol...

Router Supervisor and Power Redundancy

A multilayer switch can provide routing functions for devices on a network, as described in Chapter 12, Multilayer Switching. If that switch happens to fail, clients have no way of having their traffic forwarded their gateway has gone away. Other multilayer switches can be added into the network to provide redundancy in the form of redundant router or gateway addresses. This chapter describes the protocols that can be used for redundant router addresses, load balancing across multiple routers,...

Scenario 1 Trunking and DTP

This scenario is built around a network of switches connected by trunking links. You need to think about how DTP operates and how trunks are negotiated (or not) between switches. Consider the network shown in Figure 20-1 and answer the questions that follow. Assume that all switches shown support DTP. 1. What is the mode of the link between Catalyst A and Catalyst B 2. Suppose that the network administrator types these commands for interface GigabitEthernet 0 1 on Catalyst B Switch(config)...

Scenario 2 VLANs Trunking and VTP

This scenario is designed to stir your thinking about VLAN and trunking connectivity. You also need to examine switch configurations and apply them to a network diagram. See the diagram shown in Figure 20-2 and answer the questions that follow. Portions of the configurations of the three Catalyst switches are shown above them. interface gigabitethernet 0 1 switchport mode access switchport access vlan 2 interface fastethernet 0 1 switchport mode access switchport access vlan 2 interface...

Scenario 3 Ether Channels

This scenario focuses on EtherChannel links between switches. See the diagram shown in Figure 20-3 and answer the questions that follow. 1. Four GigabitEthernet interfaces on Catalyst A are to be bundled into a Gigabit EtherChannel with Catalyst B. If each of these interfaces also is configured as a trunk, what must be similar about them on both switches 2. Catalyst A should actively initiate an EtherChannel with Catalyst B. PAgP negotiation should be used. What commands should be used on each...

Scenario 4 Traditional STP

This scenario exercises your ability to think through the Spanning Tree Protocol operation. You are presented with a simple network of two switches. This keeps the STP complexity to a minimum while forcing you to think through the STP convergence process on a live network. Given the network diagram shown in Figure 20-4, complete the following exercises. Figure 20-4 Network Diagram for Scenario 4 1. Manually compute the spanning-tree topology. Note which switch is the root bridge, which ports...

Scenario 5 Advanced STP

A small network consists of two core switches, Catalyst C1 and C2, and an access switch, A1, as shown in Figure 20-5. Advanced Spanning Tree Protocol features will improve the convergence times and reduce the number of STP instances. Answer these questions. Figure 20-5 Network Diagram for Scenario 5 - , . . Bt VLAN 99 Catalyst A1 r I , , 1. To prevent the possibility of a unidirectional link occurring on switch A1's uplinks, what switch feature can be used What commands are necessary to enable...

Scenario 6 Router Redundancy with Hsrp Vrrp and GLBP

This scenario covers two methods by which you can configure multilayer switches to provide redundant router or gateway functionality HSRP, VRRP, and GLBP. A network consists of two VLANs 101 and 102. Suppose that the PCs in VLAN 101 (192.168.101.0 24) use address 192.168.101.1 as their default gateway. The PCs in VLAN 102 (192.168.102.0 24) use 192.168.102.1. 1. What commands are necessary to configure HSRP on a Catalyst switch so that it becomes the active router for VLAN 101 and the standby...

Scenario 7 IP Telephony in a Switched Network

This scenario uses a simple two-switch network to reinforce the concepts needed to properly implement IP telephony. Think about supplying power to the Cisco IP Phone, as well as how to implement QoS trust within this network. Use Figure 20-7 as a reference for the following questions. Figure 20-7 Network Diagram for Scenario 7 Figure 20-7 Network Diagram for Scenario 7 1. Assume that Catalyst B supports Power over Ethernet. If interface Fa1 0 1 has its default configuration, will power be...

Scenario 8 Securing Access and Managing Traffic in a Switched Network

This scenario is designed to stir your thinking about how to control access to switched networks, how to control traffic within a VLAN, and how to monitor traffic. 1. Network administrators want to have tight control over hosts moving around within their network. A Catalyst 3750 needs to have port-level security enabled on all 48 of its FastEthernet access-layer ports. Only one host should be connected per port, so the default behavior of shutting down the port is acceptable. What commands are...

Scenario 9 Implementing a Wireless LAN

This scenario is designed to stir your thinking about how to add WLAN components to an existing switched campus network, and how to extend network connectivity to wireless users. In this scenario, a Cisco Wireless LAN Controller (WLC) is positioned at the network core, and Cisco Lightweight Access Points (LAPs) are positioned at the access layer switches. Use Figure 20-8 as a reference for the questions that follow. 1. Suppose that LAP1 is configured to use 802.11g channel 1. What channel...

Shared Network Model

In the early 1990s, campus networks traditionally were 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 had distance limitations and limitations on the number of devices that could be connected to a single LAN. Network availability and performance declined as the number of connected devices increased. For example, an Ethernet LAN required all devices to share the...

Sizing AP Cells

The size of AP cells determines the number of APs that must be purchased and deployed to cover an area however, your design should not be driven by the cost alone. AP cell size can also affect the performance of the APs as clients move around or gather in one place. Remember that a WLAN is a shared medium. Within a single AP cell, all the clients associated with that AP must share the bandwidth and contend for access. If the cell is large, a large number of clients could potentially gather and...

Spanning Tree Instances Within MST

MST was designed to interoperate with all other forms of STP. Therefore, it also must support STP instances from each. This is where MST can get confusing. Think of the entire enterprise network as having a single CST topology so that one instance of STP represents any and all VLANs and MST regions present. The CST maintains a common loop-free topology while integrating all forms of STP that might be in use. To do this, CST must regard each MST region as a single black box bridge because it has...

STP Root Bridge

STP and its computations are predictable however, other factors might subtly influence STP decisions, making the resulting tree structure neither expected nor ideal. As the network administrator, you can make adjustments to the spanning-tree operation to control its behavior. The location of the Root Bridge should be determined as part of the design process. You can use redundant links for load balancing in parallel, if configured correctly. You can also configure Spanning Tree Protocol (STP)...

Strategies for Exam Preparation

The strategy you use to prepare for the BCMSN exam might be slightly different than strategies used by other readers, mainly based on the skills, knowledge, and experience you already have obtained. For example, if you have attended the BCMSN course, you might take a different approach than someone who learned switching through on-the-job training. Regardless of the strategy you use or the background you have, this book is designed to help you get to the point that you can pass the exam with...

Supplying Power to a Device

A switch first offers a default power allocation to the powered device. On a Catalyst 3750-24-PWR, for example, an IP Phone first receives 15.4W (0.32 amps at 48V DC). For Cisco ILP, inline power is provided over data pairs 2 and 3 (RJ-45 pins 1,2 and 3,6) at 48V DC. For IEEE 802.3af, power can be supplied in the same fashion (pins 1,2 and 3,6) or over pairs 1 and 4 (RJ-45 pins 4,5 and 7,8). Now the device has a chance to power up and bring up its Ethernet link, too. The power budget offered to...

Switch Port Configuration

Chapters 1, Campus Network Overview, and 2, Modular Network Design, dealt with the logical processes that you can use to design a campus network. Connections between switch blocks were discussed so that traffic can be transported efficiently across the campus. Single connections, load balancing, and redundant paths connected switches in modular blocks for complete connectivity. However, these paths were only functional paths no specifics were presented about how much traffic the network could...

Tables Used in Switching

Catalyst switches maintain several types of tables to be used in the switching process. The tables are tailored for Layer 2 switching or MLS and are kept in very fast memory so that many fields within a frame or packet can be compared in parallel. All Catalyst switch models use a CAM table for Layer 2 switching. As frames arrive on switch ports, the source MAC addresses are learned and recorded in the CAM table. The port of arrival and the VLAN both are recorded in the table, along with a time...

The Roaming Process

What enables a client to roam in the first place First, adjacent APs must be configured to use different nonoverlapping channels. For example, APs operating under 802.11b or 802.11g must use only channels 1, 6, and 11. An AP using channel 1 must not be adjacent to other APs using channel 1. This ensures that clients will be able to receive signals from a nearby AP without interference from other APs. The roaming process is driven entirely by the wireless client driver not by the AP. The client...

Topology Changes and RSTP

Recall that when an 802.1D switch detects a port state change (either up or down), it signals the Root Bridge by sending topology change notification (TCN) BPDUs. The Root Bridge, in turn, must signal the topology change by sending out a TCN message that is relayed to all switches in the STP domain. RSTP detects a topology change only when a nonedge port transitions to the Forwarding state. This might seem odd because a link failure is not used as a trigger. RSTP uses all of its rapid...

Trademark Acknowledgments

All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized. Cisco Press or Cisco Systems, Inc. cannot attest to the accuracy of this information. Use of a term in this book should not be regarded as affecting the validity of any trademark or service mark. The Cisco Press self-study book series is as described, intended for self-study. It has not been designed for use in a classroom environment. Only Cisco Learning Partners displaying...

Traditional WLAN Architecture

In Chapter 17, Wireless LAN Overview, and Chapter 18, Wireless Architecture and Design, the wireless LAN (WLAN) architecture centered around the wireless access point (AP). Each AP served as the central hub of its own BSS, where clients located with the AP cell gained an association. The traffic to and from each client had to pass through the AP in order to reach any other part of the network. Notice that even though an AP is centrally positioned to support its clients, it is quite isolated and...

Troubleshooting an Ether Channel

If you find that an EtherChannel is having problems, remember that the whole concept is based on consistent configurations on both ends of the channel. Here are some reminders about EtherChannel operation and interaction EtherChannel on mode does not send or receive PAgP or LACP packets. Therefore, both ends should be set to on mode before the channel can form. EtherChannel desirable (PAgP) or active (LACP) mode attempts to ask the far end to bring up a channel. Therefore, the other end must be...

Troubleshooting STP

Because the STP running in a network uses several timers, costs, and dynamic calculations, predicting the current state is difficult. You can use a network diagram and work out the STP topology by hand, but any change on the network could produce an entirely different outcome. Then, figure in something like PVST+, in which you have one instance of STP running for each VLAN present. Obviously, simply viewing the STP status on the active network devices would be better. You can display...

Troubleshooting VLANs and Trunks

Remember that a VLAN is nothing more than a logical network segment that can be spread across many switches. If a PC in one location cannot communicate with a PC in another location, where both are assigned to the same IP subnet, make sure that both of their switch ports are configured for the same VLAN. If they are, examine the path between the two. Is the VLAN carried continuously along the path If there are trunks along the way, is the VLAN being carried across the trunks To verify a VLAN's...

Tuning Spanning Tree Convergence

STP uses several timers, a sequence of states that ports must move through, and specific topology change conditions to prevent bridging loops from forming in a complex network. Each of these parameters or requirements is based on certain default values for a typical network size and function. For the majority of cases, the default STP operation is sufficient to keep the network loop free and enable users to communicate. However, in certain situations, the default STP can cause network access to...

Tuning the Port ID

The fourth criteria of an STP decision is the port ID. The port ID value that a switch uses is actually a 16-bit quantity 8 bits for the port priority and 8 bits for the port number. The port priority is a value from 0 to 255 and defaults to 128 for all ports. The port number can range from 0 to 255 and represents the port's actual physical mapping. Port numbers begin with 1 at port 0 1 and increment across each module. (The numbers might not be consecutive because each module is assigned a...

Tuning the Root Path Cost

The Root Path Cost for each active port of a switch is determined by the cumulative cost as a BPDU travels along. As a switch receives a BPDU, the port cost of the receiving port is added to the root path cost in the BPDU. The port or port path cost is inversely proportional to the port's bandwidth. If desired, a port's cost can be modified from the default value. NOTE Before modifying a switch port's path cost, you should always calculate the Root Path Costs of other alternative paths through...

Udld

In a campus network, switches are connected by bidirectional links, where traffic can flow in two directions. Clearly, if a link has a physical layer problem, the two switches it connects detect a problem and the link is shown as not connected. What would happen if just one side of the link (receive or transmit) had an odd failure, such as malfunctioning transmit circuitry in a gigabit interface converter (GBIC) or Small Form-Factor Pluggable (SFP) modules In some cases, the two switches still...

Verifying CEF

CEF operation depends on the correct routing information being generated and downloaded to the Layer 3 forwarding engine hardware. This information is contained in the FIB and is maintained dynamically. To view the entire FIB, use the following EXEC command Switch show ip cef Example 12-11 shows sample output from this command. Example 12-11 Displaying the FIB Contents for a Switch On this switch, only VLAN 1 has been configured with the IP address 192.168.199.1 255.255.255.0. Notice several...

Verifying Gateway Redundancy

To verify the operation of the features discussed in this chapter, you can use the commands listed in Table 13-4. In particular, look for the active, standby, or backup routers in use. Table 13-4 Gateway Redundancy Verification Commands Table 13-4 Gateway Redundancy Verification Commands

Verifying InterVLAN Routing

To verify the configuration of a Layer 2 port, you can use the following EXEC command Switch show interface type mod num switchport The output from this command displays the access VLAN or the trunking mode and native VLAN. The administrative modes reflect what has been configured for the port, whereas the operational modes show the port's active status. You can use this same command to verify the configuration of a Layer 3 or routed port. In this case, you should see the switchport (Layer 2)...

Verifying Power over Ethernet

You can verify the power status for a switch port with the following EXEC command Switch show power inline type mod num Example 14-2 provides some sample output from this command. If the class is shown as n a, Cisco ILP has been used to supply power. Otherwise, the IEEE 802.3af power class (0 through 4) is shown. Example 14-2 Displaying PoE Status for Switch Ports CAUTION A Catalyst switch waits for 4 seconds after inline power is applied to a port to see whether an IP Phone comes alive. If...

Verifying Voice VLAN Operation

You can verify the switch port mode (access or trunk) and the voice VLAN by using the show interface switchport command. As demonstrated in Example 14-3, the port is in access mode and uses access VLAN 10 and voice VLAN 110. Example 14-3 Verifying Switch Port Mode and Voice VLAN Switch show interfaces fastEthernet 1 0 1 switchport Administrative Trunking Encapsulation negotiate Operational Trunking Encapsulation native Trunking Native Mode VLAN 1 (default) Administrative Native VLAN tagging...

Virtual LANs

Consider a network design that consists of Layer 2 devices only. For example, this design could be a single Ethernet segment, an Ethernet switch with many ports, or a network with several interconnected Ethernet switches. A full Layer 2-only switched network is referred to as a flat network topology. A flat network is a single broadcast domain, such that every connected device sees every broadcast packet that is transmitted. As the number of stations on the network increases, so does the number...

VLAN Trunk Configuration

Use the following commands to create a VLAN trunk link Switch(config) interface type mod port Switch(config-if) switchport Switch(config-if) switchport trunk encapsulation isl dotlq negotiate Switch(config-if) switchport trunk native vlan vlan-id Switch(config-if) switchport trunk allowed vlan vlan-list all add except remove vlan-list Switch(config-if) switchport mode trunk dynamic desirable auto A switch port must be in Layer 2 mode before it can support a trunk. To accomplish this, you use...

VLAN Trunking Protocol

When VLANs are defined and used on switches throughout an enterprise or campus network, the administrative overhead can easily increase. Using the VLAN Trunking Protocol (VTP) makes VLAN administration more organized and manageable. This chapter covers VTP and its configuration. A similar standards-based VLAN-management protocol for IEEE 802.1Q trunks is called GARP VLAN Registration Protocol (GVRP). The GARP and GVRP protocols are defined in the IEEE 802.1D and 802.1Q (clause 11) standards,...

VTP Configuration

By default, every switch operates in VTP server mode for the management domain NULL (a blank string), with no password or secure mode. If the switch hears a VTP summary advertisement on a trunk port from any other switch, it automatically learns the VTP domain name, VLANs, and the configuration revision number it hears. This makes it easy to bring up a new switch in an existing VTP domain. However, be aware that the new switch stays in VTP server mode, something that might not be desirable. TIP...

VTP Modes

To participate in a VTP management domain, each switch must be configured to operate in one of several modes. The VTP mode determines how the switch processes and advertises VTP information. You can use the following modes Server mode VTP servers have full control over VLAN creation and modification for their domains. All VTP information is advertised to other switches in the domain, while all received VTP information is synchronized with the other switches. By default, a switch is in VTP...

Warning and Disclaimer

This book is designed to provide information about selected topics for the Building Converged Cisco Multilayer Switched Networks (BCMSN) exam for the CCNP certification. Every effort has been made to make this book as complete and as accurate as possible, but no warranty or fitness is implied. The information is provided on an as is basis. The authors, Cisco Press, and Cisco Systems, Inc. shall have neither liability nor responsibility to any person or entity with respect to any loss or damages...

Who Should Read This Book

This book is not designed to be a general networking topics book, although it can be used for that purpose. This book is intended to tremendously increase your chances of passing the Cisco BCMSN exam. Although other objectives can be achieved from using this book, the book is written with one goal in mind to help you pass the exam. The BCMSN exam is primarily based on the content of the Building Converged Cisco Multilayer Switched Networks (BCMSN) 3.0 CCNP course. You should have either taken...

Wireless Client Operation

Wireless devices can be purchased from a variety of vendors, each with its own set of features and requirements. As well, wireless clients can exist as internal or external adapters installed in PC platforms. They can also be embedded in other devices such as cell phones, wireless phones, PDAs, medical devices, and tags used for location tracking. These are usually called application-specific devices (ASDs). If you use Cisco APs in your network, knowing whether each wireless device is indeed...

Wireless LAN Cells

An AP can provide WLAN connectivity to only the clients within its range. The signal range is roughly defined by the AP's antenna pattern. In an open-air setting, this might be a circular shape surrounding an omnidirectional antenna. At least the pattern will appear as a circle on a floorplan keep in mind that the pattern is three-dimensional, also affecting floors above and below, in a multilevel building. The AP's location must be carefully planned so that its range matches up with the...

WLAN Building Blocks

At the most basic level, a wireless medium has no inherent organization. For example, a PC with wireless capability can simply bring up its wireless adapter anywhere at any time. Naturally, there must be something else that can also send and receive over the wireless media before the PC can communicate. TIP In IEEE 802.11 terminology, any group of wireless devices is known as a service set. The devices must share a common service set identifier (SSID), which is a text string included in every...

WLAN Channel Layout

To minimize channel overlap and interference, AP cells should be designed so that adjacent APs use different channels. With 802.11b and 802.11g, you are limited to using channels 1, 6, and 11. The cells could be laid out in a regular, alternating pattern, as Figure 18-6 illustrates. Figure 18-6 Holes in an Alternating Channel Pattern in 802.11b g Figure 18-6 Holes in an Alternating Channel Pattern in 802.11b g However, notice what is happening in the center where the cells meet there is a small...

WLC Functions

Once LWAPP tunnels are built from a WLC to one or more lightweight APs, the WLC can begin offering a variety of additional functions. Think of all the puzzles and shortcomings that were discussed for the traditional WLAN architecture as you read over the following list of WLC activities Dynamic channel assignment The WLC chooses and configures the RF channel used by each LAP, based on other active access points in the area. Transmit power optimization The WLC sets the transmit power of each LAP...

Strategies for the Exam

Try to schedule the exam far enough in advance that you have ample time for study. Consider the time of day and even the day of the week so that you choose a time frame that suits your daily routine. Because the exam lasts 90 minutes, you should make sure that the exam time does not coincide with your regular lunchtime or some other part of the day when you are usually tired or trying to wake up. As for the day of the week, your work schedule might prevent you from studying a few days before...

For More Information

If you have any comments about the book, you can submit those via the ciscopress.com website. Just go to the website, select Contact Us, and type in your message. Cisco might make changes that affect the CCNP certification from time to time. You should always check cisco.com for the latest details. Also, you can look to www.ciscopress.com title 1587201712, where we will publish any information pertinent to how you might use this book differently in light of Cisco's future changes. For example,...

Root Guard

After an STP topology has converged and becomes loop free, switch ports are assigned the following roles Root port The one port on a switch that is closest (with the lowest root path cost) to the Root Bridge. Designated port The port on a LAN segment that is closest to the root. This port relays, or transmits, BPDUs down the tree. Blocking port Ports that are neither root nor designated ports. Alternate port Ports that are candidate root ports (they are also close to the Root Bridge) but are in...

InterVLAN Routing

Recall that a Layer 2 network is defined as a broadcast domain. A Layer 2 network also can exist as a VLAN inside one or more switches. VLANs essentially are isolated from each other so that packets in one VLAN cannot cross into another VLAN. To transport packets between VLANs, you must use a Layer 3 device. Traditionally, this has been a router's function. The router must have a physical or logical connection to each VLAN so that it can forward packets between them. This is known as interVLAN...