Lowe D. Networking For Dummies

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Book V

Chapter 1

Setting Up a

Wireless Network

407

Wireless Access Points

Figure 1-3:

A typical

wireless

networking

adapter.

Wireless Access Points

Unlike cabled networks, wireless networks don’t need a hub or switch. If all

you want to do is network a group of wireless computers, you just purchase

a wireless adapter for each computer, put them all within 300 feet of each

other, and voilà! — instant network.

But what if you already have an existing cabled network? For example, sup-

pose that you work at an office with 15 computers all cabled up nicely, and

you just want to add a couple of wireless notebook computers to the net-

work. Or suppose that you have two computers in your den connected to

each other with network cable, but you want to link up a computer in your

bedroom without pulling cable through the attic.

That’s where a wireless access point, also known as a WAP, comes in. A WAP

actually performs two functions. First, it acts as a central connection point

for all your computers that have wireless network adapters. In effect, the

WAP performs essentially the same function as a hub or switch performs for

a wired network.

Second, the WAP links your wireless network to your existing wired network

so that your wired computer and your wireless computers get along like one

big happy family. Sounds like the makings of a Dr. Seuss story. (“Now the

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408

Wireless Access Points

wireless sneeches had hubs without wires. But the twisted-pair sneeches

had cables to thires. . . .”)

Wireless access points are sometimes just called access points, or APs. An

access point is a box that has an antenna (or often a pair of antennae) and

an RJ-45 Ethernet port. You just plug the access point into a network cable

and then plug the other end of the cable into a hub or switch, and your wire-

less network should be able to connect to your cabled network.

Figure 1-4 shows how an access point acts as a central connection point for

wireless computers and how it bridges your wireless network to your wired

network.

Infrastructure mode

When you set up a wireless network with an access point, you are creat-

ing an infrastructure mode network. It’s called infrastructure mode because

the access point provides a permanent infrastructure for the network. The

access points are installed at fixed physical locations, so the network has

relatively stable boundaries. Whenever a mobile computer wanders into the

range of one of the access points, it has come into the sphere of the network

and can connect.

Figure 1-4:

A wireless

access

point

connects

a wireless

network to

a cabled

network.

Notebook

Wireless Access

Point

10BaseT

Switch

Notebook

Computer

Wireless Network 10BaseT Network

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Book V

Chapter 1

Setting Up a

Wireless Network

409

Wireless Access Points

An access point and all the wireless computers that are connected to it are

referred to as a Basic Service Set, or BSS. Each BSS is identified by a Service

Set Identifier, or SSID. When you configure an access point, you specify the

SSID that you want to use. The SSID is often a generic name such as wire-

less, or it can be a name that you create. Some access points use the MAC

address of the WAP as the SSID.

Multifunction WAPs

Wireless access points often include other built-in features. For example,

some access points double as Ethernet hubs or switches. In that case, the

access point will have more than one RJ-45 port. In addition, some access

points include broadband cable or DSL firewall routers that enable you to

connect to the Internet. For example, Figure 1-5 shows a Linksys BEFW11S4

wireless access point router. I have one of these little guys in my home. This

inexpensive (about $60) device includes the following features:

Figure 1-5:

A typical

wireless

router.

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410

Roaming

✦ An 802.11b wireless access point that lets me connect a notebook com-

puter and a computer located on the other side of the house because I

didn’t want to run cable through the attic.

✦ A four-port 10/100 MHz switch that I can connect up to four computers

to via twisted-pair cable.

✦ A DSL/cable router that I connect to my cable modem. This enables all the

computers on the network (cabled and wireless) to access the Internet.

A multifunction access point that’s designed to serve as an Internet gateway

for home networks sometimes is called a residential gateway.

Roaming

You can use two or more wireless access points to create a large wireless

network in which computer users can roam from area to area and still be

connected to the wireless network. As the user moves out of the range of

one access point, another access point automatically picks up the user and

takes over without interrupting the user’s network service.

To set up two or more access points for roaming, you must carefully place

the WAPs so that all areas of the office or building that are being networked

are in range of at least one of the WAPs. Then, just make sure that all the

computers and access points use the same SSID and channel.

Two or more access points joined for the purposes of roaming, along with all

the wireless computers connected to any of the access points, form what’s

called an Extended Service Set, or ESS. The access points in the ESS are usu-

ally connected to a wired network.

One of the current limitations of roaming is that each access point in an ESS

must be on the same TCP/IP subnet. That way, a computer that roams from

one access point to another within the ESS retains the same IP address. If

the access points had a different subnet, a roaming computer would have to

change IP addresses when it moved from one access point to another.

Wireless bridging

Another use for wireless access points is to bridge separate subnets that

can’t easily be connected by cable. For example, suppose that you have

two office buildings that are only about 50 feet apart. To run cable from one

building to the other, you’d have to bury conduit — a potentially expensive

job. Because the buildings are so close, though, you can probably connect

them with a pair of wireless access points that function as a wireless bridge

between the two networks. Connect one of the access points to the first

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Book V

Chapter 1

Setting Up a

Wireless Network

411

Configuring a Wireless Access Point

network and the other access point to the second network. Then, configure

both access points to use the same SSID and channel.

Ad-hoc networks

A wireless access point is not necessary to set up a wireless network. Any

time two or more wireless devices come within range of each other, they

can link up to form an ad-hoc network. For example, if you and a few of your

friends all have notebook computers with 802.11b/g wireless network adapt-

ers, you can meet anywhere and form an ad-hoc network.

All of the computers within range of each other in an ad-hoc network are

called an Independent Basic Service Set, or IBSS.

Configuring a Wireless Access Point

The physical setup for a wireless access point is pretty simple: You take it

out of the box, put it on a shelf or on top of a bookcase near a network jack

and a power outlet, plug in the power cable, and plug in the network cable.

The software configuration for an access point is a little more involved, but

still not very complicated. It’s usually done via a Web interface. To get to

the configuration page for the access point, you need to know the access

point’s IP address. Then, you just type that address into the address bar of a

browser from any computer on the network.

Multifunction access points usually provide DHCP and NAT services for the

networks and double as the network’s gateway router. As a result, they typi-

cally have a private IP address that’s at the beginning of one of the Internet’s

private IP address ranges, such as 192.168.0.1 or 10.0.0.1. Consult the docu-

mentation that came with the access point to find out more.

If you use a multifunction access point that is both your wireless access

point and your Internet router and you can’t remember the IP address, run

the IPCONFIG command at a command prompt from any computer on the

network. The Default Gateway IP address should be the IP address of the

access point.

Basic configuration options

Figure 1-6 shows the main configuration screen for a Linksys BEFW11S4 wire-

less access point router that is pictured in Figure 1-5. I called up this configu-

ration page by entering 192.168.1.1 in the address bar of a Web browser and

then supplying the login password when prompted.

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412

Configuring a Wireless Access Point

Figure 1-6:

The main

configuration

page for

a Linksys

wireless

router.

This configuration page offers the following configuration options that are

related to the wireless access point functions of the device. Although these

options are specific to this particular device, most access points have simi-

lar configuration options.

✦ Enable/Disable: Enables or disables the device’s wireless access point

functions.

✦ SSID: The Service Set Identifier used to identify the network. Most

access points have well-known defaults. You can talk yourself into think-

ing that your network is more secure by changing the SSID from the

default to something more obscure, but in reality, that only protects you

from first-grade hackers. By the time most hackers get into the second

grade, they learn that even the most obscure SSID is easy to get around.

So I recommend that you leave the SSID at the default and apply better

security measures, as described in the next chapter.

✦ Allow broadcast SSID to associate? Disables the access point’s periodic

broadcast of the SSID. Normally, the access point regularly broadcasts

its SSID so that wireless devices that come within range can detect the

network and join in. For a more secure network, you can disable this

function. Then, a wireless client must already know the network’s SSID

in order to join the network.

✦ Channel: Lets you select 1 of 11 channels on which to broadcast. All the

access points and computers in the wireless network should use the

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Book V

Chapter 1

Setting Up a

Wireless Network

413

Configuring a Wireless Access Point

same channel. If you find that your network is frequently losing connec-

tions, try switching to another channel. You may be experiencing inter-

ference from a cordless phone or other wireless device operating on the

same channel.

Switching channels is also a friendly way for neighbors with wireless

networks to stay out of each other’s way. For example, if you share a

building with another tenant who also has a wireless network, you can

agree to use separate channels so that your wireless networks won’t

interfere with each other. Keep in mind that this doesn’t give you any

real measure of security because your neighbor could secretly switch

back to your channel and listen in on your network. So you still need to

secure your network as described in the next chapter.

✦ WEP — Mandatory or Disable: Lets you use a security protocol called

wired equivalent privacy. I have more to say about this in the next chapter.

DHCP configuration

You can configure most multifunction access points to operate as a DHCP

server. For small networks, it’s common for the access point to also be the

DHCP server for the entire network. In that case, you need to configure the

access point’s DHCP server. Figure 1-7 shows the DHCP configuration page

for the Linksys WAP router. To enable DHCP, you select the Enable option

and then specify the other configuration options to use for the DHCP server.

Figure 1-7:

Configuring

DHCP for

a Linksys

wireless

router.

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414

Configuring Windows XP for Wireless Networking

Larger networks that have more demanding DHCP requirements are likely

to have a separate DHCP server running on another computer. In that case,

you can defer to the existing server by disabling the DHCP server in the

access point.

For more information on configuring a DHCP server, please refer to Book IV,

Chapter 3.

Configuring Windows XP for Wireless Networking

The first step in configuring Windows XP for wireless networking is to install

the appropriate device driver for your wireless network adapter. To do that,

you need the installation CD that came with the adapter. Follow the instruc-

tions that came with the adapter to install the drivers.

Windows XP has some nice built-in features for working with wireless net-

works. You can configure these features by opening the Network Connections

folder. Choose Start➪Control Panel and then double-click the Network

Connections icon. Right-click the wireless network connection and then choose

Properties to bring up the Properties dialog box. Then, click the Wireless

Networks tab to display the wireless networking options shown in Figure 1-8.

Figure 1-8:

Configuring

wireless

networking

in Windows

XP.

Each time you connect to a wireless network, Windows XP adds that net-

work to this dialog box. Then, you can juggle the order of the networks

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Book V

Chapter 1

Setting Up a

Wireless Network

415

Using a Wireless Network with Windows XP

in the Preferred Networks section to indicate which network you’d prefer

to join if you find yourself within range of two or more networks at the

same time. You can use the Move Up and Move Down buttons next to the

Preferred Networks list to change your preferences.

To add a network that you haven’t yet actually joined, click the Add button.

This brings up the dialog box shown in Figure 1-9. Here, you can type the

SSID value for the network that you want to add. You can also specify other

information, such as whether to use data encryption, how to authenticate

yourself, and whether the network is an ad-hoc rather than an infrastructure

network.

Figure 1-9:

Adding a

wireless

network in

Windows

XP.

Using a Wireless Network with Windows XP

Windows XP also has some nice built-in features that simplify the task of

using a wireless network. For example, when your computer comes within

range of a wireless network, a pop-up balloon appears in the taskbar, indicat-

ing that a network is available.

If one of your preferred networks is within range, clicking the balloon auto-

matically connects you to that network. If Windows XP doesn’t recognize

any of the networks, clicking the balloon displays the dialog box shown in

Figure 1-10. With this dialog box, you can choose the network that you want

to join (if more than one network is listed) and then click Connect to join the

selected network.

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416

Using a Wireless Network with Windows XP

Figure 1-10:

Joining a

wireless

network in

Windows

XP.

After you’ve joined a wireless network, a network status icon appears in the

notification area of the taskbar. You can quickly see the network status by

hovering the mouse cursor over this icon; a balloon appears to indicate the

state of the connection. For more detailed information, you can click the

status icon to display the Wireless Network Connection Status dialog box,

shown in Figure 1-11.

Figure 1-11:

The

Wireless

Network

Connection

Status

dialog box

(Windows

XP).

This dialog box provides the following items of information:

✦ Status: Indicates whether you are connected.

✦ Duration: Indicates how long you’ve been connected.

✦ Speed: Indicates the current network speed. Ideally, this should say 11

Mbps for an 802.11b network, or 54 Mbps for an 802.11a or 802.11g network.

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