N10-009 Question 165
Single answerService set identifier (SSID), Basic service set identifier (BSSID), Extended service set identifier (ESSID)A network administrator is troubleshooting roaming issues in a corporate office with three wireless access points on the same floor. All three access points are configured with the network name CorpWiFi and the same WPA2-Enterprise settings to allow users to move between conference rooms without reconnecting manually. During a site survey, the administrator notices that a user's laptop sees multiple entries in the wireless analyzer, each with a different MAC address but associated with CorpWiFi. Which statement best explains what the administrator is observing?
- A
Each access point is advertising a unique SSID, and the laptop combines them into one ESSID named CorpWiFi.
- B
The different MAC addresses are BSSIDs for individual access points, while CorpWiFi is the SSID shared across an ESS to support roaming.
- C
CorpWiFi is the BSSID for the wireless network, and each MAC address represents a separate ESSID used for load balancing.
- D
The laptop is detecting hidden SSIDs, and the different MAC addresses indicate multiple VLANs mapped to the same wireless network.
Show answer and explanation
Correct answer: B
Explanation
This scenario tests the practical distinction between SSID, BSSID, and ESS/ESSID in an enterprise WLAN. The SSID is the service set identifier, or the network name users select, such as CorpWiFi. A BSSID identifies a specific basic service set, typically one AP radio, and is usually the MAC address seen in wireless analysis tools. When multiple APs share the same SSID, security configuration, and connectivity to the same distribution system, they form an Extended Service Set (ESS), which supports client roaming across coverage areas. In real deployments, survey and troubleshooting tools often display the same SSID associated with several BSSIDs, which is expected behavior in a properly designed roaming environment. This aligns with IEEE 802.11 wireless LAN concepts and common enterprise WLAN design practices used by vendors such as Cisco, Aruba, and others.
- A. Incorrect.
Incorrect. In this scenario, the access points are not advertising unique SSIDs. They are all using the same SSID, CorpWiFi, specifically so clients can recognize one logical network. An ESS consists of multiple access points using the same SSID and security settings, not multiple unique SSIDs merged by the client.
- B. Correct.
Correct. The SSID is the human-readable network name, such as CorpWiFi. Each individual radio cell from an access point is identified by a BSSID, which is typically the radio's MAC address. When multiple APs advertise the same SSID and are connected to the same distribution system, they form an ESS or ESSID-based roaming environment, allowing clients to move between APs with less disruption.
- C. Incorrect.
Incorrect. A BSSID is not the network name shown to users; it is the identifier for a specific basic service set and is usually represented by a MAC address. CorpWiFi is the SSID, not the BSSID. Also, ESSID is commonly used informally to refer to the extended service set's network name, not as separate identifiers per AP for load balancing.
- D. Incorrect.
Incorrect. Hidden SSIDs are not indicated simply because multiple MAC addresses appear for the same network name. Seeing multiple MAC addresses with the same SSID is normal in multi-AP deployments. The MAC addresses represent different BSSIDs, not VLANs. VLAN mapping may exist behind the scenes, but it is not what these analyzer results are directly showing.