What to Look For When Using 802.11b Networking

Because they are so common now, Access Points are sometimes called broadband wireless routers. This is because most of the APs on the market today include a port that can be used to connect to a broadband Internet connection, such as a cable/DSL modem. Things to look for when purchasing an AP include the following:

• Broadband support, as mentioned previously

• Dynamic Host Configuration Protocol service (DHCP)

• Network Address Translation (NAT)

• RJ-45 ports

If you are going to use the Access Point only in a closed network, the broadband connection won't be necessary. However, you will be hard-pressed to find an Access Point that doesn't have this port. DHCP enables clients to obtain IP configuration from the Access Point. A DHCP server uses a private address range (one that is not valid for use on the Internet). When making a connection to the Internet, the Access Point substitutes its IP address in packets the client sends out onto the Internet. When packets for the client are returned to the Access Point, it removes its own address and replaces the client's address. This technique is known as Network Address Translation. Using NAT and a private address range enables you to use a single Internet connection and share it with two or more computers. A second benefit of NAT is that it helps keep other computers on the Internet from gaining addressing information about the computers on your local network. Although not a perfect firewall solution, NAT can prevent simple attempts at intrusion.

DHCP is usually employed by Internet service providers (ISPs). This is because the IP address space used on the Internet is finite, and there aren't enough addresses to go around for all the computers that connect to the Internet. Thus, if you have a broadband connection for your Access Point, network packets going to and from the Internet are going through two levels of NAT! The first level is between the ISP and your wireless Accent Point. The second is between the Accent Point and a client computer on the wireless network.

For more information about Network Address Translation, see Chapter 49, "Firewalls." DHCP is covered in Chapter 29, "BOOTP and Dynamic Host Configuration Protocol (DHCP)."

An Access Point that also has a few RJ-45 ports enables you to connect computers to the Access Point using a wired connection. This feature is useful when you only need to use wireless networking for a few computers (such as laptops that you move around the home or office), while other wired computers (such as a desktop workstation or server) are located in a fixed location. Another reason for using an Access Point that provides both wired ports and wireless networking is that 802.11b operates at speeds ranging from 1Mbps to 11Mbps. Although these rates may be sufficient for some computers, servers and other client computers that transfer large amounts of data are candidates for a wired 100Mbps connection. Thus, you get the best of both types of networking. This also enables you to add wireless capabilities to computers over time, allowing you to spread out your expenses when buying wireless network cards.

Note

802.11a wireless networks operate at rates up to 54Mbps. Although this is less than 100Mbps you can achieve using a wired connection, it might be sufficient for servers and some clients in your network, especially laptop computers.

Distance Limitations

In general, 802.11b networks can span a distance up to 100 meters indoors and up to 300 meters outdoors. However, such seemingly trivial things as buildings , trees (as well as the weather), and other similar barriers can dramatically reduce this distance. When planning for the installation of a wireless network that will require more than one Access Point, because of distance limitations, start with just one Access Point, and test using it at different parts of the building. Using this method, you can determine how many Access Points will be needed. Don't count on the distances provided for in the 802.11b specifications. Additionally, if you are going to use more than one type of network adapter card ”such as one for laptop computers and another for desktop computers ”or cards from different manufacturers, then be sure to perform the same tests using each type of adapter.

Firewalls

In addition to NAT, some Access Points come with minimal firewall capabilities. For example, you can use port blocking and packet filtering to help protect your LAN. Although not a necessity, a firewall, along with a good antivirus program, will help to protect your wireless network from many of the malicious attacks that periodically occur on the Internet. Even if the Access Point does provide a simple firewall, you should probably go the extra mile and buy a software-based firewall for each computer in your network that uses other firewall techniques. The costs for these programs is minimal (usually around $50). When you consider the time it takes to restore data from backups when a virus, a worm, or another similar program invades your computer, $50 is not much to pay for the extra security that a firewall and an antivirus program can give you.

Note

NAT and firewalls are covered in greater detail in Chapter 49. This is recommended reading for anyone who is thinking about connecting any LAN to the Internet. In addition, all chapters in Part VIII, "System and Network Security," should be required reading material for anyone who operates a network in which a high degree of security is desired.