Installation Type
Let’s say you just bought a wireless NIC for your laptop and a WAP. What can you do with them? Well, that all depends on the type of installation you are going to do with these devices.
There are two major installation types: ad-hoc and infrastructure mode. Each 802.11 wireless network device is capable of being installed in one of these two modes.
Ad-Hoc Mode
The simplest installation type for wireless 802.11 devices is ad-hoc mode. In this mode, the wireless NICs (or other devices) can communicate directly without the need for a WAP. A good
example of this is two laptops with wireless NICs installed. If both cards were set up for ad-hoc mode, they could connect and transfer files (assuming the other network settings, such as protocols,
were set up correctly).
To set up a basic ad-hoc wireless network, all you need are two wireless NICs and two computers. Install the cards into the computers according to the manufacturer’s directions. During
the installation of the software, you will be asked at some point if you want to set up the NIC in ad-hoc mode or infrastructure mode. For an ad-hoc network, choose the ad-hoc mode setting.
Then bring the computers within range (90–100m) of each other.The computers will “see” each other and you will be able to connect to each other.
NOTE:
In order to transfer files, both computers will need to have security settings that will allow it.
Figure 6.6 shows an example of an ad-hoc wireless network. Note the absence of an access point.
FIGURE 6 . 6 A wireless network in ad-hoc mode
The most common use for wireless networking equipment is to provide the wireless equivalent of a wired network. To do this, all 802.11 wireless equipment has the ability to operate in what
is known as infrastructure mode. In this mode, NICs will only communicate with an access point (instead of each other as in ad-hoc mode). The access point will facilitate communication
between the wireless nodes as well as communication with a wired network (if present). In this mode, wireless clients appear to the rest of the network as standard, wired nodes. Figure 6.7 shows a typical infrastructure mode wireless network. Note the access point and
that it is connected to the wired network.
FIGURE 6 . 7 A wireless network in infrastructure mode
When configuring a client for wireless infrastructure mode, you need to understand a couple of basic wireless concepts: SSID and security. The SSID (short for Security Set Identifier) is the
unique 32-character identifier that represents a particular wireless network. All devices participating in a particular wireless network must be configured with the same SSID. If a wireless network
is to have more than one access point that provides access to the same wireless network, the access points must all have the exact same SSID.
NOTE:
Multiple access points with the same SSID spread over a large area allow a user to move around that area while maintaining a connection to the wireless network. This process is called roaming.
Because most access points are configured by default to broadcast their SSID so wireless clients can browse and find them, and because wireless signals can travel long distances (even outside
of a building), security is extremely important on wireless LANs. To that end, most access points have one or more of the following security measures in place: WEP Short for Wired Equivalent Privacy, this protocol, when enabled, requires that both
access point and workstation are configured with the same 64-bit, 128-bit, 152-bit, or 256-bit encryption key in order to communicate. This key is manually configured by the network
administrator and usually comprises a string of alphanumeric or hexadecimal characters.
NOTE:
You may also see WEP referred to as the Wired Equivalency Protocol, although that is not the original term for which the acronym was used.
MAC List Some WAPs are capable of restricting which clients can connect to the AP by keeping track of authorized MAC addresses. The administrator configures the AP with the list of all
the MAC addresses of wireless NICs that are authorized to connect to that AP. If a NIC with a MAC address not on the AP’s MAC list tries to connect, it will be rejected. Disabling SSID Broadcast By default, WAPs broadcast their SSID to make it easier for clients
to find them. For example, Windows XP has a built-in utility that allows users to browse for WAPs. However, you can turn this feature off. You then must configure each client with the
SSID of the WAP that client will connect to.
Real World Scenario
War Driving
Wireless networks are everywhere these days. Electronics retailers are selling wireless access points for less than $100 and they are flying off the shelves. You can find WAPs in public places
like shopping malls, coffee shops, airports, and hotels. In some cities, you can walk in a downtown area and find WAPs in almost every business. This proliferation of WAPs has led to a new hobby for the technologically savvy with time on their hands: war driving. This is the practice of driving around in a car with a laptop, a wireless NIC, and a high gain antenna to locate open WAPs (especially those with high-speed Internet access). There are various software programs that make this process easier (some even have Global Positioning System (GPS) interface software to make relocating the open access point again even easier). War drivers can be a threat because they can potentially access anything on
your wireless LAN (and anything it’s attached to). In addition, they are potentially consuming resources on your network. But, the threat is low in most cases. If you notice slow-moving vehicles
outside your home or business (especially those with computer equipment inside), you might be the target of a war driver.
TIP:
These features by themselves aren’t completely secure, but using multiple wireless security features together will make a wireless LAN much more secure.
Signal Degradation
Another factor to consider when installing a wireless network is signal degradation. Because the 802.11 wireless protocols use radio frequencies, the signal strength varies according to many
factors. The weaker the signal, the less reliable the network connection will be, and thus the less usable as well. These factors are included in the following list:
Distance This one should be fairly obvious. The farther away from the WAP you get, the weaker the signal. Most APs have a very limited maximum range (less than 100m for most systems).
To some degree, this can be extended using amplifiers or repeaters or using different antennas. Walls The more walls a wireless signal has to pass through, the more attenuated (reduced) the
signal becomes. Also, the thicker the wall, the more it interrupts the signal. In an indoor office area with lots of walls, the range of wireless could be a low as 25m. Protocols Used Another factor that determines the range of wireless LAN is the protocol used.
The various wireless 802.11 protocols have different maximum ranges. As discussed earlier in Table 6.2, you can see that the maximum effective range varies with the 802.11 protocol used.
Interference The final factor that affects wireless performance is outside interference. Since 802.11 wireless protocols operate in the 900 MHz, 2.4GHz, 5GHz range, interference can come from several sources, including other wireless devices, such as Bluetooth, cordless telephones, microwave ovens (a huge adversary of 802.11b and 802.11g), cell phones, other wireless
LANs, and any other device that transmits radio frequency (RF) near the frequency bands that the 802.11 protocols use.
Hardware Installation
The installation of 802.11 equipment is fairly simple. There are really two main types of components
in 802.11 networks: WAPs and NICs. Wireless NIC installation is just like installing any other network card (which you will learn later in this chapter). But, once it’s installed, you must connect to a WAP. WAP installation is fairly simple as well. Take it out of the box, connect the antenna(e), if necessary, and power, and place the WAP where it can reach the most clients. This last part is
probably the trickiest. You must place the WAP in such a way that it is servicing the most clients. This will involve a little common sense and a little trial and error. Knowing that walls
obstruct the signal, wide open spaces are better indoors. Also, it should be placed away from sources of RF interference, so right near all the other office equipment is probably not the best
place for an AP. You might have to move the AP around a bit to get the most signal strength for all the clients that need to use it.
Once you have the hardware installed, it is time to configure it properly.
Hardware/Software Configuration
Now that you have both the AP and NIC installed, you must configure them to work together. This isn’t as tricky as it sounds. Most wireless equipment is designed to work almost without
configuration. The only things you need to configure are customization settings (name, network address, etc.) and security settings.
NIC Configuration
Windows XP includes software to automatically configure a wireless connection and it installs this software automatically when you install a wireless NIC. The first time you reboot after the
installation of the NIC, you will see a screen like the one shown in Figure 6.8. This is the Windows wireless configuration screen. From this screen, you can see any available wireless networks
and configure how a computer connects to them. You can also configure several of the properties for how this wireless NIC connects to a particular wireless network:
Use Windows to Configure My Wireless Settings This check box determines whether or not Windows XP will configure the wireless settings. When it’s unchecked, Windows XP will need
an external program to configure how it connects to a wireless network, as is the case with some wireless NICs that have their own software program for this purpose. It is usually best to let
Windows XP manage your wireless settings.
Available Networks This list shows of all the wireless networks within range. The networks are listed by their SSID. From this list, you can choose which network you wish to connect to, and you
can configure how your workstation connects by clicking the Configure button. If you don’t see the wireless network you are looking for, and you are in range, click the Refresh button.
Preferred Networks This list details any wireless networks you have connected to before and want to connect to again automatically. If there is more than one wireless network in range, this list determines the order in which the workstation will try to connect to them. You can change this order using the Move Up and Move Down buttons. In addition to the general configuration, you may have to configure the encryption for the connection (if the wireless connection you are using requires it). To set up how your workstation uses encryption for a particular connection, from the screen shown in Figure 6.8, click the SSID of the wireless network you want to configure, and then click Configure. You will then see
the screen shown in Figure 6.9. From this screen, you can configure several parameters for the specific connection:
Network Name If for some reason the SSID of the WAP changes, you can change the name of the WAP you are connecting to in this field. Just delete the old one and type in the new name.
Wireless Network Key (WEP) This section contains all the parameters for configuring encryption for this connection. If the network you are connecting to uses WEP encryption,
this is the section where you will click the check boxes and configure how the wireless connection uses WEP, the key it uses, and what type of key it is. The following parameters are in
this section:
Data Encryption (WEP Enabled) If the network uses a key to encrypt data sent over the network, you should make sure this box is checked (it is checked by default). You will then
need to specify the key in the box labeled Network Key. You will also need to specify what type of key it is (ASCII or hex) by selecting the appropriate item from the drop-down list.
Network Authentication (Shared Mode) If your WAP uses shared mode authentication, you must check this box to ensure that your workstation will authenticate to the WAP using the
shared key. Often, the key is provided automatically by the WAP during the response to the initial request. If this is the case, you must check the checkbox labeled The Key Is Provided for Me
Automatically (the default). Otherwise, uncheck it and enter the key and related information in the appropriate boxes.
This Computer Is a Computer-to-Computer (Ad Hoc) Network Check this check box if you are connecting to another computer instead of an access point.
Once you have changed any settings you need to, click OK to save the changes and finish the configuration.
FIGURE 6 . 8 Windows XP wireless configuration screen
FIGURE 6 . 9 Configuring encryption
WAP Configuration
In addition to configuring the workstation(s), you must configure the WAP. There are literally hundreds of different WAPs out there, and each uses a different method to configure its internal
software. But, for the most part, they follow some general patterns.
First of all, out of the box, the WAP should come configured with an IP address (usually something similar to 192.168.1.1; check the documentation that comes with the AP to be sure).
You can take the WAP out of its box, plug it into a power outlet, and connect it to your network. But, in order for it to work, you’ve got to configure its IP address scheme to match your
network’s. To do that, you’ve usually got to do a little sleight of hand. Start by configuring a workstation on the wired network with an IP address (192.168.1.2 or similar) and subnet mask
on the same subnet as the WAP’s. You should then be able to connect to the AP to begin the configuration progress. Usually this is done either with a web browser or with a manufacturer-supplied configuration program. Once you have successfully connected to the WAP, you can configure its parameters. The following are a few parameters common to WAPs that must be configured at a minimum for the
AP to work properly.
NOTE:
Some of these parameters may require a complete WAP restart once they’ve been changed and this can interrupt your connection to the WAP (it may even require you to completely change your IP address on your workstation).
SSID As discussed earlier, this is the name of the wireless network that this AP will advertise. If this new WAP is to be part of an existing wireless network, it should be configured with the
same SSID as the existing network. In a network with only one WAP, you can think of the SSID as the “name” of the AP.
NOTE:
The SSID should not be confused with the WEP passphrase. See the discussion on WEP later in this section for details.
WAP IP Addresses Even though most WAPs come preconfigured with an IP address, it may not match the wired network’s IP addressing scheme. To that end, you should configure the
WAP’s IP addresses (including the address, subnet mask, and default gateway addresses) to match the wired network it is to be connected to.
Operating Mode (Access Point or Bridge) Access points can operate in one of two main modes: Access Point mode or Bridging mode. Access Point mode allows the WAP to operate as
a traditional access point to allow a wireless client transparent access to a wired network. On the other hand, two WAPs set to Bridging mode provide a wireless bridge between two wired
network segments.
Password Every access point has some kind of default password that is used to access the WAP’s configuration. However, for security reasons, you should change this as soon as you are
able to connect to and configure the WAP.
Wireless Channel 802.11 wireless networks can operate on different channels to avoid interference. Most wireless WAPs can be set to work on a particular channel from the factory, so for security reasons, you should change it as soon as you can.
WEP This is not a requirement, per se, but enabling it is advisable. WEP security is one of those parameters that should be enabled as soon as you turn the WAP on. WEP allows data to be encrypted before being put over the wireless connection. Configuring WEP means enabling it and choosing a key to be used for the connections.
NOTE:
You will likely be asked to enter one or more human-readable passphrases,
which are considered to be shared keys, or secret passwords that are never
sent over the wire. After entering each one, you will generally click a button to
initiate a one-way hash to produce a WEP key of a size related to the number of
bits of WEP encryption you choose. Entering the same passphrase on a wireless
client causes the hash (not the passphrase) to be sent from the wireless client
to the AP during a connection attempt. Most configuration utilities allow
multiple keys to be generated in case the administrator is granting temporary
access to the network and does not wish to divulge the primary passphrase.
This key can be deleted after the temporary access is no longer needed without
affecting access by primary LAN participants.
Hotel Wireless
For the last few years or so, I’ve been consulting with local hotels about the best way to offer in-room high-speed Internet. As you can well imagine, if your competitor is offering Internet,
you’d better as well. Now most hotels in Fargo, ND can’t afford to completely wire every room with Ethernet. With 100 rooms (on average) and an average cost of $105 per “drop,” just the
cabling installation could run into $10,000 easily.
I was able to help local hotels install wireless Internet in the main areas of the hotel and in a majority of the rooms for under $1,000. I simply installed an RF access point in the first floor and
by using special antennas, could get signal reception in almost all of the rooms in the hotel. Now, they didn’t all have the same signal level. The farther a guest was from the access point,
the weaker the signal. And, there were some rooms that were too far away from the access point to get a useable signal. But considering the price difference, many hotels were able to
take advantage of the features of wireless networking.
