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Wireless Local Area Networks
Wireless Local Area Networks (WLANs) transmit information via electromagnetic waves (such as radio) or light. Historically, wireless data networks have been very insecure, often relying on the (perceived) difficulty in attacking the confidentiality or integrity of the traffic. This perception is usually misplaced.
The most common form of wireless data networking is the 802.11 wireless standard, and the first 802.11 standard that provides reasonable security is 802.11i.
DoS and Availability
WLANs have no way to assure availability. An attacker with physical proximity can launch a variety of Denial-of-Service attacks, including simply polluting the wireless spectrum with noise. If you think of the CIA triad as a three-legged stool, “wireless security” is missing a leg. Critical applications that require a reliable network should use wired connections.
Unlicensed Bands
A “band” is a small amount of contiguous radio spectrum. Industrial, Scientific, and Medical (ISM) bands are set aside for unlicensed use, meaning you do not need to acquire a license from an organization such as the Federal Communications Commission (FCC) to use them. Many wireless devices such as cordless phones, 802.11 wireless, and Bluetooth use ISM bands. Different countries use different ISM bands: two popular ISM bands used internationally are 2.4 and 5 GHz.
FHSS, DSSS, and OFDM
Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS) are two methods for sending traffic via a radio band. Some bands, like the 2.4-GHz ISM band, can be quite polluted with interference: Bluetooth, some cordless phones, some 802.11 wireless, baby monitors, and even microwaves can broadcast or interfere with this band. Both DSSS and FHSS are designed to maximize throughput while minimizing the effects of interference.
DSSS uses the entire band at once, “spreading” the signal throughout the band. FHSS uses a number of small frequency channels throughout the band and “hops” through them in pseudorandom order.
Orthogonal Frequency-Division Multiplexing (OFDM) is a newer multiplexing method, allowing simultaneous transmission using multiple independent wireless frequencies that do not interfere with each other.
802.11
802.11 wireless has many standards, using various frequencies and speeds. The original mode is simply called 802.11 (sometimes 802.11-1997, based on the year it was created), which operated at 2 megabits per second (Mbps) using the 2.4 GHz frequency; it was quickly supplanted by 802.11b, at 11 Mbps. 802.11g was designed to be backwards compatible with 802.11b devices, offering speeds up to 54 Mbps using the 2.4 GHz frequency. 802.11a offers the same top speed, using the 5 GHz frequency.
802.11n uses both 2.4 and 5 GHz frequencies, and is able to use multiple antennas with multiple-input multiple-output (MIMO). This allows speeds up to 600 Mbps. 802.11ac uses the 5 GHz frequency only, offering speeds up to 1.3 Gbps. Finally, 802.11ax uses the 2.4, 5, and 6 GHz bands, offering speeds up to 10 Gbps. Table 5.8 summarizes the major types of 802.11 wireless.
Table 5.8 Types of 802.11 Wireless.
| Type | Top Speed | Frequency |
|---|---|---|
| 802.11 | 2 Mbps | 2.4 GHz |
| 802.11a | 54 Mbps | 5 GHz |
| 802.11b | 11 Mbps | 2.4 GHz |
| 802.11g | 54 Mbps | 2.4 GHz |
| 802.11n | 72–600 Mbps | 2.4 and/or 5 GHz |
| 802.11ac | 422 Mbps–1.3 Gbps | 5 GHz |
| 802.11ax | Up to 10 Gbps | 2.4, 5, and/or 6 GHz |
The 2.4 GHz frequency can be quite crowded: some cordless phones and baby monitors use that frequency, as does Bluetooth and some other wireless devices. Microwave ovens can interfere with 2.4 GHz devices. The 5 GHz frequency is usually less crowded, and often has less interference than 2.4 GHz. As 5 GHz is a higher frequency with shorter waves, it does not penetrate walls and other obstructions as well as the longer 2.4 GHz waves. 6 GHz (used by 802.11ax, aka Wi-Fi 6) is even less crowded.