Copyright Goodheart-Willcox Co., Inc. 454 Security Essentials access points in a network. The APs controlled by a WLC are sometimes referred to as lightweight access points (LWAPs) since they do not make any forwarding decisions. Instead, all data is forwarded to the WLC. Controller-based APs are preferred solutions in network scenarios that contain multiple access points because a network or security administrator can make wide- spread configuration changes at a centralized switch as opposed to making multiple changes on each AP. Figure 14-5 outlines the steps taken for authentication using controller-based access points. Band Selection The IEEE 802.11 standard specifies two frequency bands on which wireless devices can operate. In telecommunication, a band is a set range of frequencies within the radio frequency (RF) spectrum. The two bands on which wireless networking operate is 2.4 GHz and 5 GHz. Some access points, referred to as dual-band, are able to oper- ate both frequencies simultaneously, which is an ideal configuration for separating data transmission. For example, normal computer traffic and phones could travel on the 2.4-GHz band. More data-intensive transmissions, such as gaming or video streaming, can be handled more efficiently on the 5-GHz band. Each of the RF bands is subdivided into segments called channels. A device can be set to use a specific channel within each frequency. Channels are measured by width, which identifies the amount of data or bandwidth that can be sent during transmission. Channel width is measured in megahertz (MHz), and the minimum channel width needed is 20 MHz. An issue to consider is the possibility of interference from an overlapping chan- nel. For example, in the 2.4-GHz band, there are 11 possible channels. Channels 1, 6, and 11 are the only channels that do not overlap. A specific problem with 2.4-GHz LWAP LWAP Matt’s computer Nicole’s computer Wireless LAN controller X In this scenario, Nicole’s transmission will be sent to the WLC for forwarding. The LWAP only receives the transmission and forwards it on. Goodheart-Willcox Publisher (computers) romvo/Shutterstock.com (LWAPs) RealVector/Shutterstock.com (WLAN controller) Aiiiza/Shutterstock.com Figure 14-5 A controller-based access point (controller-based AP) is an access point that receives and transmits wireless traffic and is managed by a wireless LAN controller (WLC).