Understanding wireless networks is an important concept if you plan on taking the Security+ exam. Much of this knowledge crosses over from Network+ but if that knowledge isn’t fresh in your mind, it’s worthwhile taking the time to review it.
Note: This blog is an excerpt from the
CompTIA Security+: Get Certified Get Ahead: SY0-301 Study Guide.
Understanding Wireless Networks
Wireless local area networks (WLANs) have become quite popular in recent years, especially in home networks. A wireless network is easy to set up and can quickly connect several computers without the need to run cables.
The significant challenge with wireless networks is security. Wireless security has improved over the years, but wireless networks are still susceptible to vulnerabilities, so it’s important to understand the basics of security when setting up a wireless network. The following figure shows a typical home wireless network. Users share a single connection to the Internet through an Internet service provider (ISP). This connection can be a regular modem, a broadband cable modem, or another method.
A wireless access point (WAP) connects to the modem to share Internet access and connects all the computers in the network. Most WAPs include physical ports for wired access and a wireless transceiver for wireless clients. In other words, some users can connect with regular twisted pair cable, and other users can connect using wireless transmissions. When used as shown in the preceding figure, the WAP also includes extra capabilities such as routing, network address translation (NAT), and more.
Since wireless networks broadcast on known frequency bands, other wireless users can often see a wireless network. This can be a curious neighbor or a dedicated war driver, driving through your neighborhood looking for open wireless networks to attack.
WAPs with routing capabilities are commonly called wireless routers. However, not all WAPs are wireless routers. Many corporate networks use WAPs simply to bridge wireless clients to the wired network.
IEEE 802.11 is a group of several protocols that define the standards for wireless networks. The following table shows some of the common wireless standards, their maximum throughput, and operating frequencies.
Not every connection to a WAP will achieve the maximum throughput. Instead, the client and WAP negotiate the highest throughput they can achieve without errors. A wireless device in the same room as the WAP will be quicker than a wireless device separated by space, walls, and floors.
Additionally, wireless devices don’t operate on exactly 2.5 GHz or 5 GHz. Instead, wireless transmissions use multiple channels within these bands. For the Security+ exam, it’s not critical to know the details of wireless transmission bands, but you should understand that the signals are transmitted over the air, and the frequencies are known. An attacker with a wireless receiver (such as a simple laptop) and a protocol analyzer (a sniffer) can easily detect and capture wireless transmissions.
Managing the Wireless Footprint
A significant vulnerability of wireless networks is that they broadcast traffic over the air. The area where wireless devices can receive wireless transmissions is the wireless network’s footprint. Anyone within the footprint of the transmitter can tune to the correct frequency and access the transmissions.
Administrators have competing goals with the footprint. Users want easy access to the WAP, so they prefer a large footprint with strong signals. However, the stronger the signal is, the easier it is for an attacker to eavesdrop and capture network traffic. From a security perspective, the goal is to limit the footprint to prevent attackers from accessing the wireless network from external locations such as a parking lot.
If you want to reduce the footprint, you can reduce the power output of the WAP. The amount of power used by the WAP determines how far it transmits. Use less power and you’ll have a weaker signal and a smaller footprint. Of course, the tradeoff is reduced performance for authorized users. If the signal is weak, the negotiated speed is slower. Some users farther away from the WAP may not be able to connect at all.
Another method to reduce the footprint is to modify the placement of the WAP’s antenna. For example, walls (especially walls with metal in them) can interfere with wireless signals. By placing the WAP behind a metal wall, you may be able to prevent the signal from going too far beyond this wall.
Additionally, you can modify the position of the antennas. For example, if you position the antennas vertically (straight up and down), the signals will radiate outwards increasing the footprint. However, if you position the antennas horizontally (parallel with the horizon or the floor) the signal radiates up and down more than it radiates outward. This is useful when transmitting a signal between floors of a building, and it also reduces the footprint outside the building.
Increasing the power level of a WAP increases the wireless coverage of the WAP. You can limit the range of wireless signals by decreasing the power levels of the WAP, and by moving or positioning the wireless antenna.
Decreasing the footprint isn’t always successful to thwart eavesdroppers. Most common wireless devices use omnidirectional antennas to receive a wireless signal from any direction. However, an attacker can create a unidirectional antenna that can receive wireless traffic from a specific direction. For example, attackers create simple cantennas (antennas using a can) to capture signals from a specific direction. They connect the wireless receiver to one end of an empty can and simply point the can toward a wireless network. By pointing the cantenna in different directions, they can home in on the exact location of a wireless network. Additionally, they can eavesdrop on wireless conversations even though they are well outside the normal footprint.
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