Wireless Networking Chapter 14.

Wireless Networking Chapter 14

Objectives Explain wireless networking standards
Describe the process for implementing Wi-Fi networks Describe troubleshooting techniques for wireless networks

Historical/Conceptual

Introduction to Wireless Networking
Wireless network uses radio frequency (RF) waves to communicate between devices Enables flexibility and mobility Uses the same OSI layers as wired networks Except first two OSI layers Differs from wired networking in type of media and protocols for transmitting and accessing data The dominant wireless implementation is Wi-Fi IEEE wireless Ethernet standard Note (p. 413): Because the networking signal is freed from wires, you’ll sometimes hear the term unbounded media to describe wireless networking.

Test Specific Wi-Fi Standards

Wi-Fi Standards Wi-Fi is by far the most widely adopted wireless networking type today Wi-Fi technologies have been around since the late 1990s Supported and standardized under the umbrella IEEE standard Examples of amendments: g and ac Note (p. 413): Wi-Fi originally stood for wireless fidelity, to make it cutely equated with high fidelity (Hi-Fi), but it doesn’t really stand for anything anymore.

802.11 Standards define how wireless devices communicate
Also address communication security established the baseline features common to all Wi-Fi standards Wireless network cards, configuration software, capability to run in multiple network styles How transmissions work Note (p. 413): It’s the same concept, but frames are not addressed and encapsulated the same way as Ethernet frames.

Hardware (1 of 3) Wireless Ethernet NICs
Same function as wired, except transmission uses radio waves Networking capabilities are built into many modern devices Can add an expansion card to desktop computers USB NICs are placeable

Figure 14.1 Wireless PCIe NIC
Hardware (2 of 3) Figure Wireless PCIe NIC

Figure 14.2 External USB wireless NIC
Hardware (3 of 3) Figure External USB wireless NIC

Wireless Access Point (WAP) (1 of 2)
Interconnects wireless network nodes with wired networks A basic WAP operates like a hub at Layer 1 Often multiple devices combined in one box Built-in switch and/or router Cross Check: Using Routers (p. 415) You’ve seen wired routers before, and wireless routers function similarly, so cross-check your memory. Think way back to Chapter 1, “Net-work Models,” and see if you can answer these questions. What can a router do for your network? Can you use a router to connect to the Internet? At what layer of the OSI seven-layer model do routers function? How do routers handle addressing? Note (p. 415): Many manufacturers drop the word “wireless” from wireless access points and simply call them access points. Furthermore, many sources abbreviate both forms, so you’ll see the former written as WAP and the latter as AP.

Wireless Access Point (WAP) (2 of 2)
Figure 14.3 Linksys device that acts as wireless access point, switch, and DSL router

Software (1 of 2) Wireless device drivers
Consult your vendor’s instructions Wireless configuration utility settings Link state Signal strength Wireless network modes Security encryption Power-saving options

Figure 14.4 Wireless client configuration utility
Software (2 of 2) Figure Wireless client configuration utility

Wireless Network Modes (1 of 4)
Ad hoc mode Also called peer-to-peer mode Uses a mesh topology Works well for small groups of computers or temporary networks Independent Basic Service Set (IBBS) Two or more wireless nodes communicating in ad hoc form

Figure Wireless ad hoc mode network

Infrastructure mode Uses one or more WAPs to connect the wireless network nodes centrally Similar to a wired star topology Basic service set (BSS) Serviced by a single WAP Extended service set (ESS) Serviced by two or more WAPs Cross Check: Topologies (p. 417) The physical topology of a network represents the connectivity between nodes. This seems as good a time as any to cross-check your knowledge of topologies, so recall Chapter 2 and answer these questions. What are the four standard topologies? What are the hybrid topologies? If you connect a wireless network in infrastructure mode to a wired Ethernet network, what topology would that combined network have? Tech Tip: EBSS vs. ESS (p. 417) Many techs have dropped the word “basic” from the Extended Basic Service Set, the early name for an infrastructure-mode wireless network with more than one WAP. Accordingly, you’ll see the initials for the Extended Basic Service Set as ESS. Using either EBSS or ESS is correct.

Figure Wireless infrastructure mode network

Range Wireless networking range is hard to define
Greatly affected by environmental factors Qualifiers such as around 150 feet and about 300 feet Actual range is about half of manufacturer’s listed maximum range

Basic Service Set Identifier (BSSID)
The most basic infrastructure mode network A BSS of one WAP and one or more wireless clients The BSSID is the same as the MAC address of the WAP IBSS nodes (ad hoc mode) generate a 48-bit string as the BSSID BSSID is added in every frame

Service Set Identifier (SSID)
Another level of naming Standard name applied to the BSS or IBSS Sometimes called a network name 32-bit identification string In the header of each frame processed by a WAP Every Wi-Fi device must share the same SSID to communicate in a network

Extended Service Set Identifier (ESSID)
A Wi-Fi network with multiple WAPs (ESS) Each WAP is connected to a central switch or switches to become part of a single broadcast domain Clients connect to whichever WAP has the strongest signal Roaming: process of changing WAP connections Most Wi-Fi devices use the term SSID

Broadcasting Frequency
Potential for interference from other wireless devices Wireless devices must operate in specific broadcasting frequencies A tech must know frequencies of other wireless devices in troubleshooting interference issues Original standards use 2.4-GHz or 5.0-GHz frequencies

Broadcasting Methods Original IEEE standard used spread-spectrum radio waves Broadcasts data in small, discrete chunks Uses different frequencies within a range

Spread-Spectrum Broadcasting Methods
Direct-sequence spread-spectrum (DSSS) Frequency-hopping spread-spectrum (FHSS) Orthogonal frequency-division multiplexing (OFDM).

Direct-Sequence Spread-Spectrum (DSSS)
Sends simultaneously on different frequencies Used by early standards Uses about 22 MHz of bandwidth Capable of greater data throughput than OFDM More prone to interference than FHSS

Frequency-Hopping Spread-Spectrum (FHSS)
Constantly shifts (hops) from frequency to frequency Sends on one frequency at a time Uses less bandwidth than DSSS (~1MHz)

Orthogonal Frequency-Division Multiplexing (OFDM)
Latest method Combines multiple frequencies of DSSS with FHSS’s hopping capability Used on all but the earliest networks

Channels (1 of 2) A channel is a portion of the spectrum
standard defined 14 channels of 20MHz each Different countries may limit channels In the U.S., WAP may use channels 1 through 11 Do not use adjacent channels on nearby WAPs Most WAPs use channels 1, 6, or 11

Channels (2 of 2) The 5.0-GHz band offers many more channels than the 2.4-GHz band There are 40 different channels in the spectrum versions that use the 5.0-GHz band use automatic channel switching

Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA)
Wireless devices cannot detect collisions Cannot listen and send at the same time If two clients were to collide, there is no simple-to-detect electrical peak Two collision avoidance methods Distributed Coordination Function (DCF) Point Coordination Function (PCF) Exam Tip (p. 419): Wired Ethernet networks use CSMA/CD. Wi-Fi networks use CSMA/CA.

DCF and PCF Only DCF is implemented
DCF specifies rules for sending data onto the network media Defines a backoff period in addition to the normal interframe gap (IFG) wait period Requires an ACK from receiving nodes Exam Tip (p. 420): Current CSMA/CA devices use the Distributed Coordination Function (DCF) method for collision avoidance. Optionally, they can use Ready to Send/ Clear to Send (RTS/CTS) to avoid collisions.

802.11b Data throughput up to 11 Mbps Range up to 300 feet Popular
Uses the crowded 2.4-GHz frequency More likely to have interference from other wireless devices Signal interference can increase latency Exam Tip (P. 420): As you read about the many speeds listed for , you need to appreciate that wireless networking has a tremendous amount of overhead and latency. WAPs send out almost continuous streams of packets that do nothing more than advertise their existence or maintain connections. Wireless devices may sometimes stall due to processing or timeouts. The end result is that only a percentage of the total throughput speed is actually achieved in real data bits getting to the applications that need them. The actual number of useful bits per second is called the goodput of the wireless network. Note (p. 421): Despite the a designation for this extension to the standard, a was available on the market after b.

802.11a (1 of 2) Devices on market after 802.11b
Different from all other standards 5-GHz frequency range Speeds up to 54 Mbps Short range: about 150 feet Never as popular as b Incompatible with b

802.11a (2 of 2) Table 14.1 802.11 Summary Standard Frequency Spectrum
Speed Range Compatibility 2.4 GHz DSSS 2 Mbps ~300’ 802.11 Table 14.2 802.11b Summary Standard Frequency Spectrum Speed Range Compatibility 802.11b 2.4 GHz DSSS 11 Mbps ~300’ n/a Table 14.3 802.11a Summary Standard Frequency Spectrum Speed Range Compatibility 802.11a 5.0 GHz OFDM 54 Mbps ~150’ n/a

802.11g Up to 54 Mbps Range of 802.11b: about 300 feet
Backward compatible with b WAP can service both b and g All g network runs in native mode Runs in mixed mode if b devices added Communications drop to 11 Mbps max

802.11n Faster and newer antenna technology
Most devices must use multiple antennas Multiple in/multiple out (MIMO) Up to 600 Mbps theoretically Many WAPs employ transmit beamforming Dual-band WAPs run at 2.4- and 5.0 GHz WAPs support b/g/n devices Exam Tip (p. 422): If an g device shows a connection type of g-ht, this means it is connecting to an n WAP running in mixed mode.

802.11ac (1 of 2) Expansion of the 802.11n standard
Incorporates additional streams Wider bandwidth Better speed Only operates in the 5.0 GHz band Multiuser Mimo (MU-MIMO) Can broadcast to multiple users simultaneously Note (p. 423): For a broadcasting method, the n and ac devices use a special version of OFDM called quadruple-amplitude modulated (QAM).

802.11ac (2 of 2) Table 14.4 802.11g Summary Standard Frequency
Spectrum Speed Range Compatibility 802.11g 2.4 GHz OFDM 54 Mbps ~300’ b Table 14.5 802.11n Summary Standard Frequency Spectrum Speed Range Compatibility 802.11n 2.4 GHz1 OFDM (QAM) 100+ Mbps ~300’ 802.11b/g/n2 1 Dual-band n devices can function simultaneously at both 2.4- and 5.0-GHz bands. 2 Many dual-band n WAPs support a devices as well as b/g/n devices. This is not part of the standard, but something manufacturers have implemented. Table 14.6 802.11ac Summary Standard Frequency Spectrum Speed Range Compatibility 802.11ac 5 GHz OFDM (QAM) Up to 1 Gbps ~300’ 802.11a

Wi-Fi Protected Setup (WPS)
A special standard created by the wireless industry to makes configuration easier Works in two modes Push button PIN method Easy to use Susceptible to various WPS attacks Exam Tip (p. 423): Expect a question about wireless authentication and authorization, comparing techniques and technologies between a shared or open network. The latter, of course, doesn’t have any authentication or authorization by default!

Wi-Fi Security Problem Three wireless security methods
Easy-to-install devices have no default security Network data frames are in radio waves Three wireless security methods MAC address filtering Authentication Data encryption Note (p. 423): All the methods used in wireless network security— authentication, encryption, MAC address filtering—can be considered network hardening techniques.

MAC Address Filtering Limits access to specific NICs
Lists MAC addresses for accepted users The list is stored in a table in the WAP Rejects frames with other MAC addresses Alternatively create an exclusion list Not scalable on a modern network Problem: hackers can spoof MAC addresses Exam Tip (p. 424): WAPs use an access control list (ACL) to enable or deny specific MAC addresses. Note that a WAP’s ACL has nothing to do with ACL in NTFS; it’s just the same term used for two different things. Exam Tip (p. 424): MAC filtering with a whitelist means you allow only specific computers to join the network. When you deny specific computers, you create a blacklist. Whitelisting and blacklisting are labor-intensive processes, with whitelisting requiring far more work.

Wireless Authentication (1 of 3)
Users with proper credentials get access Can use a centralized security database Requires extra steps for wireless users 802.1X standard RADIUS server Extensible Authentication Protocol (EAP) password encryption

RADIUS server Provides authentication for network access Enables access to user’s rights on the network Client wireless computer is called a supplicant WAP is the Network Access Server (NAS) NAS contacts the RADIUS server RADIUS server checks the security database User is given access if credentials are correct Note (p. 424): RADIUS stands for Remote Authentication Dial In User Service. Say that five times.

Figure Authenticating using RADIUS

Wireless Authentication Problem Areas (1 of 3)
Connection between devices must be secure PPP between supplicant and WAP/NAS IPsec between NAS and RADIUS server RADIUS server uses an authentication protocol (EAP) WAP and wireless NICs must use the same authentication scheme

Figure Authentication using RADIUS with protocols in place

Figure Setting EAP authentication scheme

Data Encryption Encryption electronically scrambles data packets
The receiving network device requires the encryption key to unscramble the packet WPA2 provides a good level of security to data packets in transit Note (p.427): The encryption/decryption works with both symmetric encryption, where both parties have the same key, and asymmetric encryption, where parties use public and private keys. Note (p. 427): By the time you read this, WPA3 will have debuted (it was announced during this writing). WPA3 solves the problem with open Wi-Fi networks (think neighborhood café), creating individual security channels. Once you connect with your portable device, in other words, nothing can snoop on your communication.

Data Encryption Using WEP
Wired Equivalent Privacy (WEP) 64- or 128-bit encryption algorithm called RC4 Uses an initialization vector (IV) of 24 bits Issues with WEP IV length uses 24 of the 64 (or 128) bits Encryption key is static and shared No user authentication Outdated and easily cracked

Wi-Fi Protected Access (WPA)
Dynamic encryption key generation Issued per user and per session Temporal Key Integrity Protocol (TKIP) 128-bit encryption key Problem: key can be broken

Wi-Fi Protected Access 2 (WPA2)
Uses Advanced Encryption Standard (AES) 128-bit block cipher Not completely hack proof Difficult enough to deter casual hackers Adding a RADIUS server for authentication enables WPA2-Enterprise Note (p. 428): CCMP stands for Counter Mode Cipher Block Chaining Message Authentication Code Protocol. Whew! That’s why we commonly just use the initials, CCMP. AES stands for Advanced Encryption Standard.

Enterprise Wireless Enterprise devices differ from SOHO devices
Robust construction Centralized management VLAN pooling Power over Ethernet Bringing personal wireless devices into the enterprise environment

Robust Device Construction (1 of 2)
Enterprise WAP is made of better materials More configurable Can swap out antennas and radios making it possible to upgrade to the latest technologies

Robust Device Construction (2 of 2)
Figure Cisco Enterprise WAP

Enterprise Wireless Administration (1 of 3)
Large number of WAPs Offload configuration job to a wireless controller Switch designed to handle multiple WAPs Thick client: configurable via its own interface Thin clients: configurable by a wireless controller Standard protocol: Lightweight Access Point Protocol (LWAPP) Note (p. 429): Wireless controllers have a number of names. Wireless Switch, Wireless LAN switch, wireless controller, etc.

Figure Configuring WAPs

Figure Wireless Controller

VLAN Pooling A large number of clients may be on a single SSID at a given moment Traditional solution Divide the WLAN into multiple broadcast domains Use routers to interconnect the domains VLAN pooling Create a pool of VLANs for a single SSID Randomly assign wireless clients to one VLAN

Power over Ethernet (PoE)
Power and Ethernet signals via Ethernet cables Good for WAPs far from power outlets The WAP and the switches must support PoE 2003: original PoE standard 802.3af Supported a maximum 15.4 watts of DC power Revised in 2009 to support 25.5 watts New amendment called 802.3at or PoE+

Implementing Wi-Fi

Steps for Installing a Wireless Network
Perform a site survey Install one or more access points Configure the access point(s) and wireless clients Test the network to verify that it works as intended

Performing a Site Survey (1 of 6)
Reveals obstacles and determine best locations for access points Main components for crating a site survey Floor plan of the area Wireless survey tools

What wireless is already there? Discover wireless networks in the same area Today’s challenge is the preexistence of high device density environments Tools are available to assist with the survey Interference sources Create a sketch of potential interference sources Plan the network to eliminate dead zones Check out the excellent Chapter 14 Show! Sim about third-party wireless utilities at It’s a cool sim about non-Microsoft implementations.

Figure AirMagnet Survey Pro

Figure Acrylic Wi-Fi

Figure Site survey with heat map

Figure Site survey with interference sources noted

Installing the Client (1 of 2)
Install Wi-Fi hardware and software PCIe NIC Install the NIC onto a free slot on the motherboard May need to attach the antenna USB NIC Install drivers and software before you connect the NIC to the computer

Installing the Client (2 of 2)
Figure Wi-Fi NIC installed

Setting Up an Ad Hoc Network (1 of 2)
Set NICs for ad hoc mode SSID Each wireless node must use the same network name IP addresses No two nodes can use the same IP address Ensure the File and Printer Sharing service is running on all nodes Try This! Ad Hoc-ing (p. 435) If you have access to a Wi-Fi-enabled device and a friend or classmate has one as well, try this! Set up your Wi-Fi for ad hoc using the configuration utility, and then try to connect with your partner. Use default settings. Once you connect with the defaults, you can start playing with your ad hoc network! If you’re in Windows 7, select Home for your network and set up a HomeGroup. Copy the sample images from one machine to another. Throw a big file into a Public folder and try copying that one, too. Then do it again, but with variations of distance and channels. How far can you separate your devices and still communicate? What happens if you change channels in the configuration utility, such as moving both devices from channel 6 to channel 4?

Setting Up an Ad Hoc Network (2 of 2)
Figure Selecting ad hoc mode in a wireless configuration utility

Setting Up an Infrastructure Network
Determine the optimal location for the WAP Configure the WAP Configure any clients to access the WAP

Placing the Access Points/Antennas (1 of 6)
Omnidirectional antenna Radiates outward from the WAP in all directions Antenna is place the in the center of the area Standard straight-wire dipole antennas are used Omnidirectional and centered does not work for every network The gain from a typical WAP is 2 dB Increase gain with one or more bigger antennas

Figure WRT54G showing two antennas

Figure Room layout with WAP in the center

Figure Dipole radiation pattern

Figure Replacement antenna on a WAP

A unidirectional antenna focuses a radio wave into a beam Various types: parabolic, dish, and Yagi Patch antennas work well for a strong signal within a room Optimal placement depends on space needs and security concerns

Configuring the Access Point (1 of 11)
Log in to the browser-based setup utility Configure the SSID (ESSID) and beacon Configure MAC address filtering Configure encryption Configure channel and frequency Configure the client

Figure Security login for Linksys WAP

Figure Linksys WAP setup screen

Figure Setting the beacon interval

Figure MAC address filtering configuration screen for a Linksys WAP

Figure Encryption key configuration screen on Linksys WAP

Figure Encryption screen on client wireless network adapter configuration utility

Figure Encryption screen with RADIUS option

Figure Changing the channel

Figure Selecting frequency

Figure Typing in an SSID manually

Extending the Network (1 of 2)
Add a WAP to create an Extended Service Set Install a wireless bridge Connect two wireless networks; or join a wireless and a wired network together Types of wireless bridges: point-to-point and point-to-multipoint

Extending the Network (2 of 2)
Figure Linksys wireless bridge device

Verify the Installation
Move traffic between computers using the wireless connection Always verify installation before leaving

Troubleshooting Wi-Fi

Logical Troubleshooting Steps
Three types of symptoms Cannot get on the wireless network Wireless connections are way too slow Wireless connection is doing weird things Exam Tip (p. 445): Be prepared for scenario questions that quiz you about the limits of the wireless standards, or what CompTIA calls wireless standard related issues. This includes throughput speeds (11-, 54-, 100+-Gbps), frequencies, distances, and channel usage. See the above standards discussions for the limitations of each standard. Exam Tip (p. 445): You can use wireless scanning tools to check for wireless channel utilization. These are software tools that give you metrics and reports about nearby devices and which one is connected to which WAP. These tools enable you to discover overworked WAPs, saturated areas, and so on, so you can deploy WAPs to optimize your network.

No Connection (1 of 3) Channel problems Wrong encryption
Overlapping channels Mismatched channels Wrong encryption Entered the wrong encryption key Symptoms: not on network, continual prompting for password, APIPA address Solution: enter the correct password

No Connection (2 of 3) Signal/power issues
Symptoms: signal loss, not able to connect Solutions: Move closer to the WAP and avoid dead spots Turn up the power Replace the omnidirectional antenna with a unidirectional antenna Upgrade to newer n or ac Note (p. 446): Interference can also cause signal loss but I choose to treat this as a separate issue later in this section. For now we are talking about simple signal loss due to insufficient power.

Figure 14.38 Increasing power on a Cisco WAP
No Connection (3 of 3) Figure Increasing power on a Cisco WAP

Slow Wireless Connections
Clear connection to an SSID Good IP address Potential causes of slowness Too many devices overworking WAPs Too much RF interference on the network Insufficient RAM Malware Other non-wireless specific issues Note (p. 447): There are plenty of reasons for a device to run slowly that have nothing to do with wireless. Don’t forget issues such as insufficient RAM, malware, and so forth.

Overworked WAPs Device saturation Bandwidth saturation Bounce
Too many devices attaching to a single SSID over time Bandwidth saturation Bounce Solutions: add extra WAPs, upgrade hardware to ac

Interference (1 of 2) Sources of radio frequency interference (RFI)
Non-Wi-Fi sources including lighting, Bluetooth, wireless phones, and microwaves Wi-Fi networks Solution: abandon the 2.4-GHz channel Scan for RF sources using some type of RF scanner/analyzer

Figure 14.39 SNR on AirMagnet
Interference (2 of 2) Figure SNR on AirMagnet

Weird Connection Open (non-encrypted) 802.11 networks Wrong SSID
Untested updates/incompatibilities Rogue access point (rogue AP): an unauthorized access point War Driving/War chalking Looking for wireless networks using omnidirectional antennas connected to laptops using wireless sniffing programs. Marking (chalking) the location.

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