300-110 Exam Preparation Material | Designing Cisco Wireless Networks

Explanation:
In Ekahau Site Survey, passive mode involves listening to beacon frames and probe responses from deployed APs without the survey laptop actively associating to any SSID. This is significantly faster than active mode because no association, DHCP, or throughput test overhead is introduced ― the surveyor simply walks the floor while Ekahau passively captures signal strength data from all visible APs simultaneously. Using two wireless adapters in passive mode provides a critical speed advantage: one adapter scans 2.4 GHz channels while the second adapter simultaneously scans 5 GHz channels. Without dual adapters, a single adapter must time-multiplex between bands, reducing the sample rate per band and either slowing the survey walk or producing sparser data. Active mode (Options B and C) is used when throughput measurements are required for specific application validation such as voice or video, but it is inherently slower due to association overhead and sequential testing. The combination of passive scanning and dual adapter configuration delivers the highest possible data collection rate per unit of walk time.
Reference: WLSD Study Guide ― Ekahau Site Survey Modes, Passive vs. Active Survey Methodology, Multi-Adapter Survey Configuration.

Explanation:
The hidden node problem is a classic RF design flaw that emerges when APs transmit at excessive power levels relative to the attenuation characteristics of the environment. In a brick-walled building, AP signals penetrate walls with significant attenuation. When an AP transmits at maximum power, its signal propagates far beyond the intended cell boundary and reaches client devices that may be physically near other APs but unable to detect the original transmitting AP due to wall attenuation between them. These clients can hear the distant AP's signal but cannot hear each other ― making them hidden from one another. This leads to simultaneous transmissions, frame collisions at the AP receiver, and dramatic throughput degradation. The 802.11 CSMA/CA mechanism depends on all stations being able to sense the medium before transmitting; hidden nodes defeat this mechanism entirely. The WLSD curriculum consistently identifies excessive AP transmit power in high-attenuation environments as a primary cause of hidden node conditions. The solution is to reduce AP transmit power so that cell sizes remain appropriate for the physical environment.
Reference: WLSD Study Guide ― RF Design Fundamentals, Hidden Node Problem, Transmit Power and Cell Size Optimization.

Explanation:
In Cisco's AP controller preference hierarchy, each AP can be configured with a primary, secondary, and tertiary controller designation. The AP will attempt to join controllers in this exact order: primary first, secondary second, and tertiary third. When no controllers from the preference list are available, the AP may fall back to any reachable controller through standard CAPWAP discovery. In this hospital deployment, the service/development controller must be the controller of last resort ― it should only receive AP associations when all other options are exhausted. Configuring the service/dev controller as the tertiary controller in the APs' preference configuration ensures exactly this behavior: APs will attempt the SSO pair (primary) first, then the third production WLC joined via mobility tunnel (secondary), and only then the service/dev controller (tertiary). This prevents development traffic from disrupting production service, and ensures production APs do not inadvertently join the service environment during partial outages. Configuring it as primary (Option A) or secondary (Option C) would allow APs to join the service controller before exhausting production options. AP failover priority (Option D) governs which APs are processed during controller recovery, not the controller preference order during join.
Reference: WLSD Study Guide ― AP Controller Preference Configuration, Primary/Secondary/Tertiary WLC Assignment, Hospital WLAN High Availability Design.

Explanation:
When configuring high availability on a Cisco access point, the AP can be configured with a maximum of three controllers: a primary controller, a secondary controller, and a tertiary controller. This three-tier hierarchy defines the failover order ― the AP first attempts to join its primary controller, then the secondary if the primary is unavailable, and finally the tertiary if both the primary and secondary are unreachable. After exhausting all three configured options, the AP enters a discovery process to find any available controller. This three-controller configuration (primary, secondary, tertiary) allows network engineers to implement N+1 redundancy where critical APs can be directed to specific backup controllers in a deliberate sequence. Limiting the configuration to only 2 controllers (as stated in Option B which would be incorrect) would reduce redundancy options for environments with geographically distributed controllers requiring specific failover paths.
Reference: WLSD Study Guide ― AP High Availability Configuration, Primary/Secondary/Tertiary Controller Assignment, AP Failover Design.

Explanation:
Cisco's mobility group architecture enables seamless client roaming between WLCs by establishing a trusted peer relationship and shared mobility domain. When two Cisco Catalyst 9800-80 WLCs are placed in the same mobility group, they establish CAPWAP mobility tunnels enabling both Layer 2 and Layer 3 roaming with session continuity including IP address preservation. Within the same mobility group, WLCs exchange client state information, allowing 802.11r Fast BSS Transition, 802.11k neighbor reports, and 802.11v BSS Transition Management to function across controller boundaries. No specific primary or secondary roles are assigned within a mobility group ― all members are peers with equal standing for roaming purposes, which is precisely what Option D describes.
Option A incorrectly implies a hierarchical structure that does not exist in mobility group peer relationships.
Option B separating the WLCs into different groups would break inter-building roaming since clients would experience a full re-authentication cycle.
Option C imposing an anchor relationship is appropriate only for guest WLANs.
Reference: WLSD Study Guide ― Mobility Group Architecture, Inter-Controller Roaming, 802.11r/k/v Fast Roaming Design.