N10-009 Question 164
Single answerService set identifier (SSID), Basic service set identifier (BSSID), Extended service set identifier (ESSID)A network administrator is troubleshooting Wi-Fi roaming issues in a warehouse. Three access points are deployed to provide seamless coverage for handheld scanners. All three APs broadcast the SSID "WarehouseWiFi" and are connected to the same wired network and VLAN. While reviewing a scanner's connection details, the administrator notices that the SSID remains the same as the user moves, but the BSSID changes from one AP radio to another. Which statement best explains this behavior?
- A
The scanner is moving between different basic service sets within a single extended service set, so the SSID stays the same while the BSSID changes to match the AP radio in use.
- B
The scanner is connected to the same basic service set, and the BSSID changes because DHCP assigns a new wireless identifier at each location.
- C
The scanner is moving between different extended service sets, and the SSID remains the same because ESSIDs must be identical across separate networks.
- D
The scanner is switching from 2.4 GHz to 5 GHz, and the SSID changes are hidden because the BSSID identifies the VLAN rather than the access point.
Show answer and explanation
Correct answer: A
Explanation
In IEEE 802.11 wireless LANs, the SSID is the human-readable network name presented to clients, such as "WarehouseWiFi." A BSSID identifies a specific basic service set, which is typically one AP radio and is commonly represented by a MAC address. When multiple APs are connected through the same distribution system and advertise the same SSID, they create an extended service set (ESS), allowing clients to roam while staying on what appears to be the same WLAN. In practice, this means a user device can keep seeing the same SSID while the BSSID changes as it reassociates to a closer or stronger AP. This behavior aligns with standard 802.11 WLAN design and enterprise best practices for seamless mobility.
- A. Correct.
Correct. A BSSID identifies a specific AP radio's basic service set, typically using the radio's MAC address. When multiple APs advertise the same SSID and support client movement across the same distribution system, they form an extended service set (ESS). In that design, the client continues to see the same network name (SSID) while roaming to a different BSSID as it associates to another AP.
- B. Incorrect.
Incorrect. A basic service set is tied to a specific AP radio, so if the BSSID changes, the client is no longer on the same BSS. DHCP does not assign the BSSID; the BSSID is associated with the access point radio, not with IP addressing or location-based reassignment.
- C. Incorrect.
Incorrect. An extended service set is made up of multiple basic service sets that usually share the same SSID to present one logical WLAN to users. The client in this scenario is not moving between different ESSs; it is roaming within one ESS. The idea that separate ESSs must keep the same SSID is a misconception.
- D. Incorrect.
Incorrect. A BSSID identifies the wireless service set provided by a specific AP radio, not a VLAN. Although different bands can have different BSSIDs, the scenario specifically describes movement between APs in a roaming environment, and the SSID does not 'hide changes' related to VLANs.