Introduction to wireless networking

Introduction to wireless networking

This chapter introduces some concepts you should understand before working with wireless networks, describes Fortinet’s wireless equipment, and then describes the factors you need to consider in planning deployment of a wireless network.

  • Wireless concepts Security Authentication
  • Wireless networking equipment
  • Automatic Radio Resource Provisioning

 

Wireless concepts

Wireless networking is radio technology, subject to the same characteristics and limitations as the familiar audio and video radio communications. Various techniques are used to modulate the radio signal with a data stream.

 

Bands and channels

Depending on the wireless protocol selected, you have specific channels available to you, depending on what region of the world you are in.

  • IEEE 802.11b and g protocols provide up to 14 channels in the 2.400-2.500 GHz Industrial, Scientific and Medical (ISM) band.
  • IEEE 802.11a,n (5.150-5.250, 5.250-5.350, 5.725–5.875 GHz, up to 16 channels) in portions of Unlicensed National Information Infrastructure (U-NII) band

Note that the width of these channels exceeds the spacing between the channels. This means that there is some overlap, creating the possibility of interference from adjacent channels, although less severe than interference on the same channel. Truly non-overlapping operation requires the use of every fourth or fifth channel, for example ISM channels 1, 6 and 11.

The capabilities of your wireless clients is the deciding factor in your choice of wireless protocol. If your clients support it, 5GHz protocols have some advantages. The 5GHz band is less used than 2.4GHz and its shorter wavelengths have a shorter range and penetrate obstacles less. All of these factors mean less interference from other access points, including your own.

When configuring your WAP, be sure to correctly select the Geography setting to ensure that you have access only to the channels permitted for WiFi use in your part of the world.

For detailed information about the channel assignments for wireless networks for each supported wireless protocol, see Reference on page 955.

 

Power

Wireless LANs operate on frequencies that require no license but are limited by regulations to low power. As with other unlicensed radio operations, the regulations provide no protection against interference from other users who are in compliance with the regulations.

Power is often quoted in dBm. This is the power level in decibels compared to one milliwatt. 0dBm is one milliwatt, 10dBm is 10 milliwatts, 27dBm, the maximum power on Fortinet FortiAP equipment, is 500 milliwatts. The FortiGate unit limits the actual power available to the maximum permitted in your region as selected by the WiFi controller country setting.

Received signal strength is almost always quoted in dBm because the received power is very small. The numbers are negative because they are less than the one milliwatt reference. A received signal strength of -60dBm is one millionth of a milliwatt or one nanowatt.

 

Antennas

Transmitted signal strength is a function of transmitter power and antenna gain. Directional antennas concentrate the signal in one direction, providing a stronger signal in that direction than would an omnidirectional antenna.

FortiWiFi units have detachable antennas. However, these units receive regulatory approvals based on the supplied antenna. Changing the antenna might cause your unit to violate radio regulations.

 

Security

There are several security issues to consider when setting up a wireless network.

 

Whether to broadcast SSID

It is highly recommended to broadcast the SSID. This makes connection to a wireless network easier because most wireless client applications present the user with a list of network SSIDs currently being received. This is desirable for a public network.

Attempting to obscure the presence of a wireless network by not broadcasting the SSID does not improve network security. The network is still detectable with wireless network “sniffer” software. Clients search for SSIDs that they know, leaking the SSID. Refer to RFC 3370. Also, many of the latest Broadcom drivers do not support hidden SSID for WPA2.

 

Encryption

Wireless networking supports the following security modes for protecting wireless communication, listed in order of increasing security.

None — Open system. Any wireless user can connect to the wireless network.

WEP64 — 64-bit Web Equivalent Privacy (WEP). This encryption requires a key containing 10 hexadecimal digits.

WEP128 — 128-bit WEP. This encryption requires a key containing 26 hexadecimal digits.

WPA — 256-bit WiFi Protected Access (WPA) security. This encryption can use either the TKIP or AES encryption algorithm and requires a key of either 64 hexadecimal digits or a text phrase of 8 to 63 characters. It is also possible to use a RADIUS server to store a separate key for each user.

WPA2 — WPA with security improvements fully meeting the requirements of the IEEE 802.11i standard. Configuration requirements are the same as for WPA.

For best security use the WPA2 with AES encryption and a RADIUS server to verify individual credentials for each user. WEP, while better than no security at all, is an older algorithm that is easily compromised. With either WEP or WAP, changing encryption passphrases on a regular basis further enhances security.

 

Separate access for employees and guests

Wireless access for guests or customers should be separate from wireless access for your employees. This does not require additional hardware. Both FortiWiFi units and FortiAP units support multiple wireless LANs on the same access point. Each of the two networks can have its own SSID, security settings, firewall policies, and user authentication.

A good practice is to broadcast the SSID for the guest network to make it easily visible to users, but not to broadcast the SSID for the employee network.

Two separate wireless networks are possible because multiple virtual APs can be associated with an AP profile. The same physical APs can provide two or more virtual WLANs.

 

Captive portal

As part of authenticating your users, you might want them to view a web page containing your acceptable use policy or other information. This is called a captive portal. No matter what URL the user initially requested, the portal page is returned. Only after authenticating and agreeing to usage terms can the user access other web resources.

For more information about captive portals, see the Captive portals chapter of the FortiOS Authentication Guide.

 

Power

Reducing power reduces unwanted coverage and potential interference to other WLANs. Areas of unwanted coverage are a potential security risk. There are people who look for wireless networks and attempt to access them. If your office WLAN is receivable out on the public street, you have created an opportunity for this sort of activity.

 

Monitoring for rogue APs

It is likely that there are APs available in your location that are not part of your network. Most of these APs belong to neighboring businesses or homes. They may cause some interference, but they are not a security threat. There is a risk that people in your organization could connect unsecured WiFi-equipped devices to your wired network, inadvertently providing access to unauthorized parties. The optional On-Wire Rogue AP Detection Technique compares MAC addresses in the traffic of suspected rogues with the MAC addresses on your network. If wireless traffic to non-Fortinet APs is also seen on the wired network, the AP is a rogue, not an unrelated AP.

Decisions about which APs are rogues are made manually on the Rogue AP monitor page. For detailed information, see Wireless network monitoring on page 894.

 

Suppressing rogue APs

When you have declared an AP to be a rogue, you have the option of suppressing it. To suppress and AP, the FortiGate WiFi controller sends reset packets to the rogue AP. Also, the MAC address of the rogue AP is blocked in the firewall policy. You select the suppression action on the Rogue AP monitor page. For more information, see Wireless network monitoring on page 894.

Rogue suppression is available only when there is a radio dedicated to scanning. It will not function during background scanning for spectrum analysis.

 

Wireless Intrusion Detection (WIDS)

You can create a WIDS profile to enable several types of intrusion detection:

  • Unauthorized Device Detection
  • Rogue/Interfering AP Detection
  • Ad-hoc Network Detection and Containment
  • Wireless Bridge Detection
  • Misconfigured AP Detection
  • Weak WEP Detection
  • Multi Tenancy Protection
  • MAC OUI Checking

For more information, see Protecting the WiFi Network on page 891.


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