Wi-Fi

Wi-Fi is the family of wireless local-area network technologies built on the IEEE 802.11 standard, which defines the physical (PHY) and media-access-control (MAC) layers for wireless networking in the 2.4 GHz, 5 GHz, and 6 GHz bands. The base standard has been amended many times — 802.11b/g/n/ac/ax (Wi-Fi 4/5/6) — each revision pushing rates and spectral efficiency; the current consolidated specification is IEEE 802.11-2020, published with later amendments through the IEEE GET program.

Naming: SSID, BSSID, ESSID

Three identifiers that are constantly confused:

• SSID — the human-readable network name, up to 32 octets, broadcast in beacon frames. This is what clients see and select.
• BSSID — the 48-bit MAC address of a specific access point’s radio for one cell of the network. Every (AP, radio, SSID-instance) cell has its own BSSID; it is how frames are actually addressed on the air, and how tools like aircrack-ng target a specific AP.
• ESSID — in a multi-AP Extended Service Set (ESS), the collection of BSSIDs that together present one logical network. In practice the ESSID string is identical to the SSID; the distinction is structural: the SSID names the network, while each AP’s BSSID names one radio serving it.

A useful mental model: SSID/ESSID answer “which network?”, BSSID answers “which exact AP radio?”.

Security relevance

• Management frames (beacons, probes, authentication, deauthentication) are sent unauthenticated and unencrypted in classic 802.11 — the root enabler of deauth attacks, rogue APs, and evil-twin phishing.
• Security lives in the link layer: WEP (broken, RC4/IV flaws), WPA, WPA2 (4-way handshake over PSK or 802.1X), and WPA3 (SAE handshake). The WPA/WPA2 4-way handshake is what aircrack-ng captures and cracks offline.
• Monitoring and attacking 802.11 requires a card that supports monitor mode and frame injection — see aircrack-ng for the standard toolchain.

Sources

• IEEE 802.11-2020 — Wireless LAN MAC and PHY Specifications
• Wikipedia — IEEE 802.11

Related

• aircrack-ng — the 802.11 assessment suite: capture, inject, crack
• watchguard-access-point-configuration — enterprise AP management (SSIDs, sites)
• vlans — trunking multiple SSID-backed networks through AP uplinks
• wifi-deauthentication-attacks — forged deauth frames: the primitive, the DEF CON instance, and 802.11w PMF