Wireless Networks
How Bandwidth Is Achieved from RF Signals
To send data over the airwaves, the IEEE has developed the 802.11 specification, which defines half-duplex operations using the same frequency for send and receive operations on a WLAN. No licensing is required to use the 802.11 standards however, you must follow the rules that the FCC has set forth. The IEEE defines standards that help to operate within the FCC rules. The FCC governs not only the frequencies that can be used without licenses but the power levels at which WLAN devices can...
Wireless LAN Fundamentals
Chapter 1 Introduction to Wireless Networking Concepts Chapter 4 WLAN Technologies and Topologies Chapter 5 Antenna Communications Chapter 6 Overview of the 802.11 WLAN Protocols Chapter 7 Wireless Traffic Flow and AP Discovery Chapter 8 Additional Wireless Technologies Chapter 9 Delivering Packets from the Wireless to Wired Network This chapter covers the following subjects Wireless Local-Area Networks A brief history of wireless networking and some of the basic concepts. How Bandwidth Is...
Modulation Techniques and How They Work
In short, the process of modulation is the varying in a signal or a tone called a carrier signal. Data is then added to this carrier signal in a process known as encoding. Imagine that you are singing a song. Words are written on a sheet of music. If you just read the words, your tone is soft and does not travel far. To convey the words to a large group, you use your vocal chords and modulation to send the words farther. While you are singing the song, you encode the written words into a...
Cisco Published 640721 Iuwne Exam Topics Covered in This Part
Describe the basics of the Cisco Unified Wireless Network architecture (Split MAC, LWAPP, stand-alone AP versus controller-based AP, specific hardware examples) Describe the Cisco Mobility Express Wireless architecture (Smart Business Communication System SBCS, Cisco Config Agent CCA, 526WLC, 521AP -stand-alone and controller-based) Describe the modes of controller-based AP deployment (local, monitor, HREAP, sniffer, rogue detector, bridge) Describe controller-based AP discovery and...
Vendor Specific Topology Extensions
The vendor-specific topology extensions are an enablement of additional network functionality by way of vendor-defined protocols, devices, and topologies. In this section you will learn how workgroup bridges, wireless repeaters, outdoor wireless bridges, and wireless mesh networks through the use of wireless controllers can enhance the functionality and capability of your wireless deployment. You will most likely have times when you have an isolated network that needs access to the rest of the...
Original 80211 Topologies
Although the previous sections discussed network topologies that you might encounter, it was a very general discussion. You also need to understand the original topologies, defined by the 802.11 committees, including the following The following sections give more details on these topologies. When two computers want to communicate directly with one another, they do so in the form of an ad hoc network. Ad hoc networks don't require a central device to allow them to communicate. Rather, one device...
Frame Types
For the most part, all frames are going to have the same type of header. The difference is in the body of the frame. The body is more specific and indicates what the frame is all about. Table 7-2 shows some frame types. Contention Free End + Acknowledgment (CF-End +ACK) Announcement traffic indication message (ATIM) Each frame type merits its own discussion to follow. Management frames, as their name indicates, are used to manage the connection. In looking at a frame capture, the Type field...
Maps and APs in the WCS
Maps in the WCS are designed to give you a visual representation of the wireless network. Not only do maps help with monitoring after a deployment, but they help in the implementation and deployment process. You can use planning mode to determine how many APs you need in an area and where to place them. To access the maps, browse to Monitor > Maps. From here you can see a list of maps, as illustrated in Figure 18-10. You start by adding a building and then adding floors. After you have the...
General Wireless Topologies
When you're talking about wireless topologies, there are a number of ways it could go. If you are talking about how your wireless network looks next to your wired network, you are most likely talking about a wireless local-area network (WLAN). The goal of a WLAN versus a wireless personal-area network (WPAN) is quite different. The following sections discuss the purpose of each network type, what they try to accomplish, and what types of wireless technologies you might encounter there. Figure...
Wireless Standards and Regulatory Committees
Many people benefit from the availability of wireless Internet access as they travel to various parts of the world. Without regulatory committees and organizations to ensure the proper use and interoperability of equipment, it's likely that people could not connect from place to place. To ensure that certain rules governing the use of wireless RF are adhered to, numerous country-specific organizations and global committees monitor standards and usage. This chapter discusses some of them. The...
LWAPP Layer 2 Transport Mode
When operating in Layer 2 mode, LWAPP has the following characteristics and require- Topic LWAPP communication between the AP and the WLC is in native, Layer 2 Ethernet frames. This is known as Layer 2 LWAPP mode. In Layer 2 LWAPP mode, although the APs might get an IP address via DHCP, all LWAPP communications between the AP and WLC are in Ethernet encapsulated frames, not IP packets. The APs must be on the same Ethernet network as the WLC. This means that Layer 2 mode is not very scalable....
Connecting to a Standalone AP
Almost any AP that is capable of operating in both autonomous and lightweight mode ships in autonomous mode. You need to convert the device to lightweight mode if you plan to use it in that mode. Luckily, you can accomplish this conversion in two ways. You can get a Windows application called the Upgrade tool to do it, and you can get it done using the Cisco Wireless Control System (WCS). Either method accomplishes the same task it is simply a matter of what you prefer and what you have access...
The Cisco WiSM
The Cisco WiSM, shown in Figure 10-10, is a services module that installs in the 6500 series switch or 7600 series router with the Cisco Supervisor Engine 720. It has the same functionality as the 4400 series standalone controllers the difference is that it supports up to 300 APs. The WiSM supports 150 access points per controller, with each blade having two controllers. Thus, you can have a total of 300 access points. You can also cluster 12 of them into a mobility domain. This allows up to...
Understanding Mobility Groups
In simple terms, a mobility group is a setting on a controller that defines the controller as a member of a group. Other controllers would also be members of that group. These controllers share information about the clients that are roaming. In Figure 12-1, two controllers are in the same mobility group. They can exchange information about the client that is roaming. Figure 12-2 shows a network with three controllers. Controllerl and Controlled are in the same mobility group, and Controller3 is...
Using the CLI to Configure the Controller
To configure the Cisco Mobility Express solution, you need a console connection to the Cisco 526. You do not need to do anything on the AP because the controller takes care of it. After you have a console connection, you can power on the device and view the boot process. In Example 15-1, notice that if you press the Esc key, you are presented with multiple boot options. The normal selection is to run the primary image. Example 15-1 Booting the Cisco 526 Controller Booting Primary Image Press...
Diversity coding
Precoding is a function that takes advantage of multiple antennas and the multipath issue that was discussed in Chapter 3, WLAN RF Principles. 802.11n uses transmit beam-forming (TxBF), which is a technique that is used when more than one transmit antenna exists where the signal is coordinated and sent from each antenna so that the signal at the receiver is dramatically improved, even if it is far from the sender. This technique is something that you would use when the receiver has only a...
Mobility Anchors
With mobility anchors, also called guest tunneling or auto anchor mobility, all the client traffic that belongs to a WLAN (especially the Guest WLAN) is tunneled to a predefined WLC or set of controllers that are configured as an anchor for that specific WLAN. This feature helps restrict clients to a specific subnet and have more control over the user Figure 12-11 Mobility Anchor Configuration Figure 12-11 Mobility Anchor Configuration traffic. Normally what happens is that a client anchors to...
Do I Know This Already Quiz Yvy
The Do I Know This Already quiz helps you determine your level of knowledge of this chapter's topics before you begin. Table 16-1 details the major topics discussed in this chapter and their corresponding quiz questions. Table 16-1 Do I Know This Already Section-to-Question Mapping Table 16-1 Do I Know This Already Section-to-Question Mapping Using Windows to Connect to a Wireless LAN Using a Mac to Connect to a Wireless LAN Using Linux to Connect to a Wireless LAN Using the ADU to Connect to a...
Using Windows to Connect to a Wireless LAN
The wireless configuration tool for Microsoft Windows is called the Windows Wireless Zero Configuration Utility (WZC). The WZC is designed to provide the basic capabilities necessary to access most WLANs however, it is not very powerful when it comes to troubleshooting utilities. Many vendors such as IBM Lenovo install a custom client that can be used to create and manage profiles as an alternative to the WZC. So when you use these vendor-installed clients, you cannot use the Windows WZC. WZC...
Common Antenna Types
The two main types of antennas are directional and omnidirectional. In this section you will learn the difference between the two types and look at some of the antennas that Cisco offers. Both send the same amount of energy the difference is in how the beam is focused. To understand this, imagine that you have a flashlight. By twisting the head of the light, you can make the beam focus in a specific area. When the beam has a wider focus, it doesn't appear to be as bright. While you twist the...
Using the CLI to Troubleshoot
Sometimes resolving the common issues is not easy and they require further research. In these cases, you can use the CLI or the GUI tool to gather additional information. From the CLI, you have a few options for troubleshooting. First, you can use show commands on the CLI to gain valuable information related to the operational status of the controller, the APs, and the clients. Many of these show commands are available in various pages of the GUI tool, as you will see in later sections of this...
The CUWN Architecture
The Cisco Unified Wireless Network defines a total of five functional areas or interconnected elements, as shown in Figure 10-2. The five elements or components all work together. It's no longer about point products, where you can buy a standalone AP and deploy it and then later get management software to handle it. Today it is all about everything working together to create a smarter, more functional network. To illustrate how it all comes together, consider a Cisco wireless network. This type...
WPAWPA2 Passphrase Profiles
You can choose to use WPA WPA2 Passphrase. This method uses encryption with a rotated encryption key and a common authentication key, called a passphrase. To configure the passphrase, click the Configure button and enter the ASCII or hexadecimal passphrase, as shown in Figure 16-22. By following the preceding steps, you can create any of the available profiles. Table 16-3 compares the different security options. Figure 16-22 WPA WPA2 Passphrase Table 16-3 Security Options Comparison Figure...
Do I Know This Already Quiz Nne
The Do I Know This Already quiz helps you determine your level of knowledge of this chapter's topics before you begin. Table 5-1 details the major topics discussed in this chapter and their corresponding quiz questions. Table 5-1 Do I Know This Already Section-to-Question Mapping Table 5-1 Do I Know This Already Section-to-Question Mapping 1. Which of the following are types of polarization (Choose all that apply.) 2. All Cisco antennas use what type of polarization 3. In an electromagnetic...
The 80211g Protocol
The IEEE ratified 802.11g in June 2003. In addition to the four data rates of 802.11b, it added eight more. The maximum data rate of 54 Mbps places 802.11g in the same speed range as 802.11a however, it remains in the 2.4-Ghz frequency range. On the lower end, 802.11g is still compatible with 802.11b, using the same modulation and coding as 802.11b for the 1-, 2-, 5.5-, and 11-Mbps rates. To achieve the higher data rates, 802.11g uses orthogonal frequency division multiplexing (OFDM) for...
Distributedcoordination interframe space DIFS Used for data frames and is the normal spacing between frames
Each of these has a specific purpose as defined by the IEEE. SIFS is used when you must send a frame quickly. For example, when a data frame is sent and must be acknowledged (ACK), the ACK should be sent before another station sends other data. Data frames use DIFS. The time value of DIFS is longer than SIFS, so the SIFS would preempt DIFS because it has a higher priority. Figure 7-1 illustrates the transmission of a frame. In the figure, Station A wants to send a frame. As the process goes,...
The Layer 2 Roaming Process
As previously discussed, Layer 2 roaming happens when a user moves to another AP but stays on the same VLAN and the same IP subnet. As far as the user is concerned, nothing special has happened. The client isn't notified that he is roaming. He also keeps his IP address, and all active transmissions stay active. This process is handled within a single controller. This process is called intracontroller roaming and takes less than 10 ms. Behind the scenes, the client, when roaming to a new AP,...
Client Misassociation
When a client connects to an AP, operating system utilities normally allow the client to save the SSID. In the future, when that SSID is seen again, the client can create a connection automatically. There is a possibility that clients will be unaware of the connection. If the SSID is being spoofed, the client could connect to a potentially unsafe network. Consider the following scenario. An attacker learns the SSID of your corporate network. Using this information, he sends beacons advertising...
Figure 112 AP States
The process begins with the discovery of a controller. Because the lightweight APs are by definition zero-touch when deployed, you should only need to plug them in and let them do the rest. On the back end, the part you do not see is a little more complex. The steps in this process, beginning with discovery, are as follows Step 1. The APs send LWAPP discovery request messages to WLCs. This is broadcast at Layer 2. Because Layer 3 mode is what you want to use, this should fail. Step 2. Upon...
Converting to LWAPP
Three methods you can use to convert the AP to lightweight mode are as follows Use the IOS to LWAPP conversion utility. This is an installable application that you can download from Cisco.com. Use the WCS. If you have a WCS, this method is probably preferred however, it is not covered as part of the CCNA wireless certification. As of July 2005, simply archive the image to the AP to convert it to LWAPP. The section that follows examines the IOS-to-LWAPP conversion. Converting to LWAPP Using the...
The Cisco 44xx Series WLC
Topi c The Cisco 44xx series Wireless LAN Controller, shown in Figure 10-8, is a standalone appliance. Figure 10-8 Cisco 4400 Series Wireless LAN Controller Figure 10-8 Cisco 4400 Series Wireless LAN Controller It is designed to take up one rack unit. It has either two or four Gigabit Ethernet uplinks, and they use mini-GBIC FSG slots. It can support 12, 25, 50, or 100 APs, depending on the model. And it can support up to 5000 MAC addresses in its database. The 4400 series has a 10 100...
Configuring the Controller Using the Web Interface
Topic For this example, you build basic wireless connectivity. The process is as follows Build the controller interface. Create the WLAN and tie it to the interface. Building the controller interface is required because, as you might recall from the beginning of this chapter, the interface is a logical entity. It is not a physical port that you can touch, although the interface you create will end up having access to the network via one of the physical ports. After you have created the...
Using the Cisco Spectrum Expert
Cisco Spectrum Expert addresses the problem of RF interference in wireless networks. With Cisco Spectrum Expert, you can detect, classify, locate, and manually mitigate sources of wireless interference. The Cisco Spectrum Expert Wi-Fi is the industry-leading spectrum intelligence product for Wi-Fi networks. Cisco Spectrum Expert Wi-Fi offers complete visibility into the RF physical layer in the 2.4-GHz and 5-GHz frequencies, allowing for enhanced performance, security, and reliability of WLAN...
Cisco Wireless LAN Adapters
Cisco offers enterprise class wireless LAN adapters in the PCI and cardbus form factors. The AIR-CB21AG-X-K9 is a cardbus model, and the AIR-PI21AG-A-K9 is the PCI model. These adapters support most advanced wireless security configurations when you use Cisco software to manage them. You can, however, use the Windows WZC, but it's better to use the ADU and Aironet System Tray Utility (ASTU) if you want all the features of the cards to be available to you. The ADU has more configuration...
Upgrading a Controller
Management tasks in the controller involve upgrading or downgrading images as well as managing configuration files. You can begin working with these files by verifying the version currently running on the controller. Figure 19-1 shows the MONITOR > Summary page, which indicates that the version of code on this particular controller is software version 4.1.192.17M (Mesh). 5.x is the current version of code, so you need to obtain the version you want to have loaded before performing the...
Monitoring with the Controller
As far as the management and monitoring of the network go, you have much power by way of the controller. The controller is a central point of intelligence that can give you valuable information regarding the network overall as well as specifics related to APs, clients, rogues, and more. The main login page of the controller provides an excellent starting point. The Controller Summary page is the first thing you see when you log in. At first glance, it might seem like a simple overview, but it...
Cisco Learning Network
Cisco provides a wide variety of CCNA wireless preparation tools at a Cisco Systems website called the Cisco Learning Network. The Cisco Learning Network includes Quick Learning Modules, interviews with Cisco's Portfolio Manager for Wireless Certifications, documents that give you a sneak peek of what's included in the Instructor-Led Training Course, and blogs and discussion forums to help you on your way. To use the Cisco Learning Network, you do not need a registered login at http www....
Determining Signal Strength Influences
Although it might seem hopeless to deploy a network that is susceptible to various forms of interference, you can fight back. To fight back, you need to know what tools are available out there for you to determine signal strength, noise levels, and potential sources of interference in the path. This section discusses these tools. To give you a little background, Augustin-Jean Fresnel was a French physicist and civil engineer who lived from 1788 to 1827. He correctly assumed that light moved in...
The Cisco Secure Services Client
The Cisco Secure Services Client (SSC) is client software that provides 802.1x (Layer 2) user and device authentication for access to both wired and wireless networks. The SSC does not need a Cisco wireless card to operate the software. It's really an alternative to the WZC, with some major benefits. From the wired network side, it provides 802.1x capabilities for user and device authentication, which is more extensive than the standard wired LAN connection. On the wireless side, it provides...
CCNA Wireless Official Exam Certification Guide
Published by Cisco Press 800 East 96th Street Indianapolis, IN 46240 USA All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without written permission from the publisher, except for the inclusion of brief quotations in a review. Printed in the United States of America First Printing October 2008...
Cisco Mobility Express
Cisco Mobility Express was designed to offer wireless services to small businesses in a form factor similar to the lightweight architecture. It is not the full Lightweight Access Point Protocol (LWAPP) but rather a subset of LWAPP functionality. This means that although the 521 AP runs the subset of LWAPP, it cannot communicate with enterprise controllers. The Cisco Mobility Express solution delivers best-in-class wireless capabilities that until recently had been reserved for enterprises. The...
The 1400 Series Wireless Bridge
The Cisco Aironet 1400 series wireless bridge, shown in Figure 10-7, is designed for outdoor environments. It has a rugged enclosure that can withstand the elements. It is designed for point-to-point or point-to-multipoint networks. It can be mounted on poles, walls, or even roofs. You can also change the polarization, which, depending on how the wireless bridge is mounted, could be a very important aspect of deploying this wireless bridge. As far as the antennas go, it has a high-gain internal...
Tools for Final Preparation
This section describes the available tools and how to access them. Exam Engine and Questions on the CD The CD in the back of the book includes an exam engine software that displays and grades a set of exam-realistic questions. The question database includes simulation (sim) questions, drag-and-drop questions, and many scenario-based questions that require the same level of analysis as the questions on the CCNA Wireless exam. Using the exam engine, you can either study by practicing using the...
How the WZC Tool Works
When a Windows-based computer boots up, the Wireless Zero Configuration reports any network that is being broadcast, usually via a balloon window at the bottom right of the screen. This is because when a WZC client attempts to access a network, it uses an active scanning process. This differs from other methods, such as passive scanning, which is used by other clients. Note The concept of passive scanning simply involves the client's waiting until it hears a beacon from an access point. With...
The Layer 3 Roaming Process
As with Layer 2 roaming, the goal of Layer 3 roaming is for a client to roam transparently. The difference is that you are working with multiple controllers on different subnets. The catch is that although the controllers are on different subnets, the user does not change IP addresses. Instead, the controllers tunnel the traffic back to the original controller. So it's a smoke-and-mirrors configuration. You are literally making the network believe that the user hasn't roamed. The two tunneling...
WLCs in the CUWN
A single WLC can manage from six to 300 access points. You can create groupings of controllers for more scalability. This type of network could easily get out of hand if you had more than 300, 600, or 900 APs. In cases such as this, a WCS application can manage a number of controllers as well as a location appliance that can help track where devices are in the network. Note There is obviously more to the solution that what has been discussed in this section. For more information on the Unified...
Administration Options in the WCS
In the WCS interface, you have tabs or horizontal menus across the top that access various configuration elements, including these Each of these menus cascade to drop-down submenus that you can access. When you log in, the page you see is called the WCS Home, which has four primary tabs that we will discuss out of the six seen in Figure 18-2 General Provides information about the inventory, the coverage, and the client count Client Provides information about the top APs by client count, clients...
Frame bridging
Part of the control traffic that is sent back and forth via LWAPP is information that provides radio resource management (RRM). This RRM engine monitors the radio resources, performs dynamic channel assignments, provides detection and avoidance of interference, and provides the dynamic transmit power control (TPC) that was discussed in Chapter 1, Introduction to Wireless Networking Concepts. Also, whenever coverage holes (such as when one AP goes down) are detected by another access point, the...
Wireless Local Area Networks
Although wireless networking began to penetrate the market in the 1990s, the technology has actually been around since the 1800s. A musician and astronomer, Sir William Her-schel (1738 to 1822) made a discovery that infrared light existed and was beyond the visibility of the human eye. The discovery of infrared light led the way to the electromagnetic wave theory, which was explored in-depth by a man named James Maxwell (1831 to 1879). Much of his discoveries related to electromagnetism were...
Wlan Rf Principles
In wireless technologies, you need to understand what influences act on wireless transmissions. This chapter reviews the characteristics of wireless transmissions and the influences that act on them, sometimes causing problems. Some of the material covered in the first section, Characteristics of Wireless Networks, is a review of information you learned in Chapter 1, Introduction to Wireless Networking Concepts. If you are comfortable with your knowledge of this information, you can just review...
Management Frame Protection
One method of Management Frame Protection (MFP) is Infrastructure MFP. With this method, each management frame includes a cryptographic hash called a Message Integrity Check (MIC). The MIC is added to each frame before the Frame Check Sequence (FCS). When this is enabled, each WLAN has a unique key sent to each radio on the AP. Then, the AP sends management frames, and the network knows that this AP is in protection mode. If the frame were altered, or if someone spoofs the SSID of the WLAN and...
The 3750G WLC
The 3750-G Wireless LAN Controller, shown in Figure 10-9, is integrated into a switch. There are two assemblies the WS-C3750G-24PS-E and the AIR-WLC4402-*-K9. The two assemblies are connected to the SEPAPCB assembly, which has two Gigabit Ethernet links connecting through SFP cables and two GPIO control cables. The major benefits of this integration into the switching platform include the following Figure 10-9 Cisco 3750-G Series Wireless LAN Controller Figure 10-9 Cisco 3750-G Series Wireless...
The Cisco 2106 WLC
The Cisco 2106 Wireless LAN Controller, shown in Figure 10-11, is also a single-rack unit design with eight 10 100 Ethernet ports. Courtesy of Cisco Systems, Inc. Unauthorized use not permitted. Figure 10-11 Cisco 2106 Series Wireless LAN Controller Courtesy of Cisco Systems, Inc. Unauthorized use not permitted. Figure 10-11 Cisco 2106 Series Wireless LAN Controller It can support up to six primary access points. It has an RJ-45 console port and two RJ-45 ports that support PoE. It has nearly...
The Cisco WLCM
The Wireless LAN Controller Module (WLCM), shown in Figure 10-12, is designed for the ISR routers. You would see this controller in a small office. It has the same functionality as the 2106, but it does not have the directly connected AP and console port. It supports six APs. The WLCM-Enhanced (WLCM-E) supports eight or 12 APs, depending on which module you get. Chapter 10 Cisco Wireless Networks Architecture 185 Of course, some limitations apply. Most of the features are similar to the 4000...
How the Air Port Extreme Tool Works
When you access the main AirPort configuration interface in Mac OSX 10.5 and above, you can disable the card, join networks, and even perform advanced configurations. To access the main AirPort interface, click the Open Apple icon and select System Preferences > Network. If you want to create a profile, select the Network Name drop-down menu. Here you can choose Join Other Network or Create Network. The Create Network option allows you to set up an ad hoc network of computer-to-computer...
WLAN Technologies and Topologies
When you work in a wireless network, you can encounter a number of technologies and deployment options. Sometimes your situation calls for a peer-to-peer connection, and other times you will want to connect to users who are in another room or on another floor, yet on the same network. In this chapter you will learn what these networks are and when they are appropriate. You will also look at which types of equipment are appropriate for certain situations and environments. Use the Do I Know This...
Influences on Wireless Transmissions
Now that you clearly understand wireless transmissions and what is involved, it is a good time to discuss the influences on wireless signals. Some influences can stop a wireless signal from propagating altogether, whereas others might simply shorten the transmission distance. Either way, you should be aware of these factors so you can plan and adjust your deployment accordingly. In this section, you learn about the Free Path Loss model, absorption, reflection, scattering, multipath, refraction,...