The words
| Term | Meaning |
|---|---|
| SSID | The network name people see, like "Staff" (up to 32 characters) |
| BSS (Basic Service Set) | One AP and the clients joined to it |
| BSSID | The MAC address of the AP's radio for that SSID: how clients tell one AP from another |
| ESS (Extended Service Set) | Several APs with the same SSID, joined by the wired LAN, so clients can roam |
| IBSS (ad hoc) | Clients talking directly, with no AP |
| Distribution system | The wired network behind the APs |
A client associates with one AP at a time. In an ESS, as it moves it measures the signal from every AP with its SSID and roams to a stronger one. Neighbouring APs should overlap their coverage by 10-15% and use different channels.
In NetLab
▶ LAP1 NetLab Windows-style command prompt. Type help to see the commands. C:\Users\student>netsh wlan show interfaces There is 1 interface on the system: Name : Wi-Fi Description : NetLab Wireless Adapter Physical address : 00:1a:15:33:10:6b State : connected SSID : Staff BSSID : 00:1a:ab:2b:5b:14 Network type : Infrastructure Radio type : 802.11ac Authentication : WPA2-Personal Cipher : CCMP Band : 5 GHz Channel : 36 Signal : 76% C:\Users\student>ipconfig Windows IP Configuration Wireless LAN adapter Wi-Fi: Connection-specific DNS Suffix . : Link-local IPv6 Address . . . . . : fe80::a494:697d:8f6e:d74c%12 IPv4 Address. . . . . . . . . . . : 192.168.30.10 Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . : 192.168.30.1 ▶ AP1 NetLab access point. Type help to see the commands. AP1> show clients Client MAC Signal LAP1 00:1a:15:33:10:6b 76%
Access point modes
| Mode | What the AP does |
|---|---|
| Local | The normal mode: serves clients (controller-based AP) |
| FlexConnect | Serves clients at a branch and can switch their traffic locally if the link to the controller fails |
| Monitor | Doesn't serve clients; scans the air for rogue APs and attacks |
| Sniffer | Captures frames on one channel and sends them to a PC running a packet analyser |
| Bridge / mesh | Links buildings or APs together over the air |
| SE-Connect | Spectrum analysis: finds non-Wi-Fi interference |
Tip: The BSSID is a MAC address, so it's how you prove which AP a laptop is really on when several share an SSID.