The following is the second part of a six-part series on wireless security. Each tip is excerpted from the Cisco Press book, Network Security First-step by Tom M. Thomas. Check back frequently for the next installment, or go to the main series page for all installments.
The term wireless networking refers to radio technology that enables two or more computers to communicate using standard network protocols such as IP, but without cables. Wireless networking hardware requires the use of underlying technology that deals with radio frequencies and data transmission. The most widely used standard is 802.11, which produced by the Institute of Electrical and Electronic Engineers (IEEE). This is a standard defining all aspects of Radio Frequency Wireless networking.
802.11b specifies that radios talk on the unlicensed 2.4GHz band at 11-Mbps transmission rate on one of 15 specific channels (in the United States, use is limited to only the first 11 of those 15 channels because of government regulations). Wireless network cards automatically search through these channels to find WLANs, so there is no need to configure client stations to specific channels. When the NIC finds the correct channel, it begins talking to the access point. As long as all the security settings on the client and AP match, communications across the AP can begin, and the user can participate as part of the network.
802.11g is a new high-speed wireless standard that allows users to transmit data at rates of up to 54 Mbps—nearly five times faster than 802.11b technology. Because it operates in the 2.4GHz frequency band, 802.11g is completely compatible with 802.11b and available for use worldwide. Apple currently has support for 802.11g in all its devices, with Cisco to follow shortly.
Modes of Operation
Two types of wireless networks are possible, and they differ on how wireless devices communicate to each other. WLANs operate either in ad-hoc or infrastructure. Ad-hoc networks have multiple wireless clients talking to each other as wireless peers to share data among themselves without the aid of a wireless access point. An infrastructure WLAN consists of several clients talking to a central device called an access point (AP), which is usually connected to a wired network like a corporate or home LAN:
Every wireless access point has a finite range within which a wireless connection can be maintained between the client computer and the access point. The actual distance varies depending on the environment; manufacturers typically state both indoor and outdoor ranges to give a reasonable indication of reliable performance. Also, note that when operating at the edge of the range limits, the performance might drop because of deterioration of the quality of the wireless signal. Typical ranges are as follows:
In most cases, separate access points are interconnected via a wired LAN by providing wireless connectivity in specific areas such as offices or classrooms. Depending on the sophistication of the access point, the range can be modified by adjusting the power level on the AP. This might or might not be an option on some of the lower-end consumer level APs; however, on the Cisco Aironet 350, 1100, and 1200 series, this is possible. The ranges are 5 mw to 100 mw, which can be a useful method of controlling how far your signal reaches outside your company walls.
If a single area is too large to be covered by a single access point, multiple access points or wireless bridges can be used. If you choose to go this route, make sure that the access points you want to use have this feature because some do not.
Bandwidth on an 802.11b network is limited to 11 Mbps per access point. To dispel a lot of confusion, 11 Mbps refers to the total possible bandwidth per access point. Many people are used to the wired world, where switches are everywhere and each device gets the full 100 Mbps to the desktop. This is not the case with wireless; the 11 Mbps is divided among all users on that access point. If ten people access the same AP, communication to the wired world will be limited to the equivalent of approximately 1 Mbps per user.
So, you can solve the problem by simply adding another access point? I have not used the "it depends rule" since Chapter 4, "Security Protocols," so its use is way overdue and I am invoking it now. It depends; the 802.11b standard does not contain any specifications for load balancing across multiple access points. Devices that strictly adhere to the standard have no solution to the problem of finding your network becoming overpopulated.
The only way to manage this issue is to add another AP in the same area with a different network name and radio channel, effectively having more than one separate network with a maximum of three in use at the same area. Again, this is if you are using devices that adhere in this regard to the 802.11 standard. In reality, many manufacturers recognized that they would be severely limited in the number of APs they could sell to businesses, so they developed proprietary load balancing solutions. Additional discussions of these solutions are beyond the scope of this book and should be referred to your vendor of choice.
Reproduced from the book Network Security First-step, ISBN 1587200996, Copyright 2004, Cisco Systems, Inc. Reproduced by permission of Pearson Education, Inc., 800 East 96th Street, Indianapolis, IN 46240. Written permission from Pearson Education, Inc. is required for all other uses. Visit www.ciscopress.com for a detailed description and to learn how to purchase this title.