Wireless Networking Basics
This domain tests radio fundamentals, the 802.11 family, and the security and design decisions that make a wireless LAN actually work.
Standards and spectrum
802.11b/g use 2.4 GHz (11 Mbps and 54 Mbps); 802.11a uses 5 GHz; 802.11n (Wi-Fi 4) uses both and adds MIMO; 802.11ac (Wi-Fi 5) is 5 GHz only; 802.11ax (Wi-Fi 6/6E) adds 6 GHz and OFDMA. Higher frequency means more channels but shorter range and worse penetration through walls.
Channels and coexistence
2.4 GHz has 11 usable channels in North America but only three non-overlapping ones: 1, 6, and 11. 5 GHz offers many non-overlapping channels; 20/40/80 MHz widths trade throughput for channel count. Wireless is a shared half-duplex medium using CSMA/CA with acknowledgements. Clients that cannot hear each other create the hidden-node problem and extra collisions.
SSIDs and security
An SSID names the network; the BSSID is the AP radio's MAC address. Open, WEP, and WPA are broken. Use WPA2 or WPA3 with AES-CCMP; WPA3 adds SAE and protected management frames. Personal mode uses a pre-shared key; Enterprise mode uses 802.1X/EAP against a RADIUS server. Disable WPS and change default admin credentials.
Worked example
An office has three APs on 2.4 GHz in one open space. Setting all three to channel 6 creates co-channel interference and halves throughput. Assign 1, 6, and 11, reduce transmit power so cells do not overlap excessively, and run a site survey to confirm coverage and signal-to-noise ratio before mounting the APs.
Traps
Assuming 5 GHz travels further than 2.4 GHz - it does not. Treating channel width as free throughput: 40 MHz in 2.4 GHz overlaps almost everything. Confusing SSID with BSSID. Believing WPA2-PSK encrypts traffic between clients on the same AP; that requires client isolation.