300-110 Designing Cisco Wireless Networks (300-110 WLSD) v1.2 Question and Answers

In an N+1 redundancy deployment, an AP ' s ability to return to its designated primary WLC after that controller recovers depends on two distinct configuration requirements working in concert. First, the AP Fallback feature (Option C) must be enabled on the WLC. AP Fallback instructs APs to monitor the availability of their configured primary controller and automatically reconnect to it when it becomes available again, rather than remaining permanently joined to the N+1 backup controller. Without AP Fallback enabled, APs stay connected to whichever controller they most recently joined. Second, the APs must have their primary WLC information correctly configured (Option D). If an AP does not have the primary controller ' s name, IP address, or FQDN correctly set, it cannot identify when its designated primary has recovered and therefore cannot initiate a return fallback. DHCP Option 43 (Option A) is used for initial AP discovery only. Secondary WLC configuration (Option B) addresses failover direction but not the return path. AP failover priority (Option E) controls which APs are moved first during a failover event, not whether fallback occurs. Reference: WLSD Study Guide — N+1 Redundancy Design, AP Fallback Configuration, Controller Primary, Secondary and Tertiary Assignment.

Cisco ' s WLAN location and asset tracking architecture (based on Cisco Spaces or legacy Cisco MSE/CMX) relies on the ability to receive and measure the RF signal from tagged assets at multiple APs simultaneously. For accurate location determination using triangulation or trilateration algorithms, a minimum of three APs must receive the tag ' s signal with sufficient RSSI. Monitor mode APs are dedicated to passive RF listening — they do not transmit client-serving SSIDs and focus their full radio attention on scanning all channels for signal measurement. Placing monitor mode APs specifically on the perimeter of an asset tracking area provides the spatial diversity and boundary detection capability needed to accurately triangulate assets throughout the interior, without requiring any modifications to the existing data/voice serving APs. Adding monitor mode APs at the perimeter as an overlay ensures the existing 2.4 GHz and 5 GHz voice/data design is entirely undisturbed. Adding local mode APs (Option B) would serve clients and compete for channel capacity. Grouping APs closer (Option C) reduces capacity and increases co-channel interference. Increasing transmit power (Option D) worsens hidden node conditions without improving location accuracy. Reference: WLSD Study Guide — Cisco Location Services, Monitor Mode APs, Asset Tracking and WLAN Overlay Design.

Receive Start of Packet (RxSOP) is a Cisco proprietary mechanism that defines the minimum received signal threshold at which an access point will acknowledge an 802.11 frame and begin processing it. In a high-density lecture hall environment with 16 APs and directional antennas on a constrained channel plan, rogue APs operating on the same or adjacent channels contribute directly to elevated channel utilization by causing unnecessary medium contention, virtual carrier sensing via NAV, and clear channel assessment deferral. By raising the RxSOP threshold on the legitimate APs, the engineer creates a higher signal floor requirement — only signals above the configured RxSOP level are processed. Signals from distant rogue APs, arriving below this threshold, are silently discarded rather than processed, preventing them from consuming airtime through CCA deferral and NAV mechanisms. Band select (Option A) encourages dual-band clients to move to 5 GHz but does not address rogue interference. 802.11w (Option B) is a management frame protection standard, not an interference mitigation tool. DFS detection (Option D) is for radar avoidance on UNII-2 channels, not rogue AP mitigation. Reference: WLSD Study Guide — High-Density WLAN Design, RxSOP Configuration, Channel Utilization Management.

To optimize roaming in a wireless network with multiple controllers, it is essential to use the same WLAN name (SSID) across all controllers. When SSIDs differ between controllers, clients perceive them as different networks and must perform a full re-association and re-authentication when roaming between APs managed by different controllers. This causes a roaming disruption equivalent to connecting to an entirely new network. By using identical SSID names on both controllers, clients can seamlessly roam between APs on different controllers within the same mobility group — the controllers exchange client state information via the mobility tunnel, enabling seamless handoff. In the scenario described, ' Copr-NET390595865WLC-1 ' and ' Copr-NET6837l638WLC-2 ' are different SSIDs, meaning clients cannot roam transparently between them. Making both controllers broadcast the same SSID name (and using a mobility group to connect the controllers) resolves this. Reference: WLSD Study Guide — SSID Consistency Across Controllers, Inter-Controller Roaming, Mobility Group Configuration.

Cisco Catalyst Center ' s AI-driven network management capabilities — including AI Analytics, AI-Enhanced RRM (Radio Resource Management), location analytics (DNA Spaces integration), and automated RF profile management — are exclusively available under the Catalyst Advantage license tier. The Advantage tier builds upon the Essentials tier and adds access to the full suite of AI/ML-powered assurance and optimization features. Specifically, AI-Enhanced RRM leverages machine learning models trained on historical RF telemetry to predict and prevent RF issues, dynamically adjust channel and power assignments, and automate RF profile selection — capabilities that cannot be activated without the Advantage license. Location analytics through Catalyst Center integrates with Cisco Spaces to provide real-time client location tracking, asset tracking, and spatial analytics. Catalyst Essentials (Option C) provides basic device management, software image management, and network plug-and-play provisioning — it does not include AI Analytics or advanced RRM automation. Right-To-Use (Option B) is a legacy licensing model not applicable to Catalyst Center. SNTC SmartNet (Option D) is a support and maintenance contract, not a software feature license. Reference: WLSD Study Guide — Cisco Catalyst Center Licensing, AI-Enhanced RRM, Catalyst Advantage Feature Set.

An active ping survey is used to validate network performance by sending and receiving data packets to measure end-to-end network performance, including latency, packet loss, and throughput. Ekahau site survey tools can perform active ping surveys to test the connectivity and performance of the wireless network while the surveyor walks the floor plan, producing a geographically correlated map of network performance metrics. This differs fundamentally from passive surveys, which only measure signal strength from beacons. A GPS-assisted survey (Option A) is used for large outdoor areas to automate location tracking. Spectrum analysis (Option B) identifies Layer 1 RF conditions but does not measure network performance. A passive survey (Option C) measures RSSI and SNR but does not test actual data connectivity or throughput. Active ping is the correct tool for validating that the network delivers the expected end-to-end service levels. Reference: WLSD Study Guide — Ekahau Survey Types, Active Survey Methodology, Post-Deployment Validation.

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.

Non-802.11 device detection on the 5 GHz band without a dedicated spectrum analyzer is possible through Cisco ' s CleanAir technology, which is embedded as an RF ASIC in many Cisco AP models including the 9120 series. CleanAir operates at the hardware layer — below the 802.11 MAC — enabling the APs to detect, classify, and report non-802.11 interference sources such as cordless phones, microwave ovens, video cameras, radar, and other unlicensed RF emitters in the 5 GHz spectrum. The WLC aggregates CleanAir reports from all APs and provides a consolidated interference device list accessible through the WLC ' s monitoring interface. Since the question specifies the 5 GHz band, the relevant 802.11 protocol for 5 GHz is 802.11a (and its successors 802.11n and 802.11ac). Exporting the list of 802.11a interferers from the WLC using the CleanAir RF ASIC correctly targets the 5 GHz band and identifies non-802.11 devices detected there. Option A incorrectly references 802.11b, which operates only on 2.4 GHz. Options B and C attempt to use the WLAN adapter for non-802.11 detection, but a standard WLAN adapter in monitor mode can only capture 802.11 frames — it cannot detect non-802.11 RF energy without a spectrum analyzer chipset. Reference: WLSD Study Guide — Cisco CleanAir Technology, Non-802.11 Interference Detection, Post-Deployment Survey Methodology.

For APs to be able to fail over between a primary SSO pair in one data center and a standalone WLC in a remote data center connected via WAN with firewalls, two design requirements must be met. First, a mobility tunnel must be created between the wireless controllers (Option A). The mobility tunnel enables the controllers to exchange mobility control messages, peer information, and eventually AP context when failover occurs. Without the mobility tunnel, the remote WLC is not recognized as a valid failover target by the APs through the mobility domain. Second, UDP ports 16666 and 16667 must be open through the firewalls between the controllers (Option D). UDP port 16666 is used for mobility control traffic and UDP port 16667 is used for mobility data traffic — both must be permitted through the firewalls at both data centers for the mobility tunnel to establish and function. HTTPS port 443 (Option B) is used for web management and API communication, not for mobility tunneling. A static RF group leader (Option C) is a RRM configuration unrelated to AP failover capability. Creating a mobility group with the same names (Option E) is a component of the configuration but alone is insufficient without the mobility tunnel and open firewall ports. Reference: WLSD Study Guide — Inter-Site WLC Failover Design, Mobility Tunnel Requirements, Firewall Port Planning for WAN-Separated Controllers.

An oil terminal presents specific wireless design constraints: the requirement is pervasive coverage (maximum geographic coverage) for low-bandwidth applications (casual web and email). These requirements prioritize coverage reach over throughput optimization. The correct approach is to keep all data rates enabled, including lower rates such as 6, 9, 12, and 18 Mbps — because in an industrial environment with challenging RF propagation paths, reflective surfaces, and potential obstructions, lower data rates extend the functional coverage range of each AP. Web and email traffic does not require high data rates; even 1-6 Mbps is sufficient for these applications. Disabling rates below 54 Mbps (Option A) would dramatically shrink each AP ' s effective coverage area, requiring many more APs for pervasive coverage and failing the primary design objective. Assigning static maximum power without RRM auto-adjustment creates excessive co-channel interference. Disabling rates below 24 Mbps (Option C) still reduces coverage reach unnecessarily. Disabling 802.11n and 802.11ac MCS rates (Option D) prevents the AP from using high-efficiency modulation for nearby clients without coverage benefit. Auto power assignment combined with all rates enabled provides the optimal balance for pervasive industrial deployment. Reference: WLSD Study Guide — Industrial WLAN Design, Coverage vs. Capacity Trade-offs, Data Rate Configuration for Pervasive Coverage.

In a Cisco Catalyst 9800 SSO deployment using Link Aggregation Group (LAG) for network interface redundancy, the SSO pair — WLC1 (active) and WLC2 (standby) — must both have their physical interfaces connected to the network infrastructure as part of the LAG bundle. LAG on the 9800 in an SSO configuration is implemented as a multi-chassis LAG across both the active and standby controllers. This means both WLC1 and WLC2 contribute physical member links to the port channel, and the connected switches must have LACP or PAgP bundle members from both controllers in the same port channel group. When an SSO failover occurs — WLC1 fails and WLC2 takes over as active — the LAG remains operational because WLC2 ' s physical links are already established members of the bundle and continue forwarding traffic without any link renegotiation. If only WLC1 had LAG connectivity and WLC2 had independent links, an SSO failover would cause a LAG topology change requiring re-convergence, introducing downtime. WLC3 is a separate N+1 backup controller joined via a mobility tunnel — not part of the SSO pair and its LAG configuration is independent. Reference: WLSD Study Guide — Catalyst 9800 SSO with LAG, Multi-Chassis Link Aggregation, High Availability Network Redundancy Design.

Metal doors cause the most signal attenuation among common building materials due to the fundamental electromagnetic properties of metal. Metal is highly reflective and absorptive of radio frequency signals — it creates what is effectively a Faraday cage effect around any room or space it encloses. In wireless design attenuation modeling tools such as Ekahau, metal is assigned the highest attenuation value among standard building materials, typically 30+ dB per surface. Cinder block walls (Option A) are dense and provide significant attenuation (10-15 dB) but are not as RF-impenetrable as solid metal. Glass walls (Option C) and office windows (Option D) have relatively low attenuation values (2-4 dB) due to the minimal RF-absorbing properties of glass. When engineers model attenuation materials in predictive survey tools, metal doors and metal-containing structures consistently produce the highest per-surface attenuation values, making them the primary barrier obstacles to plan around. Reference: WLSD Study Guide — RF Signal Attenuation, Building Material Attenuation Values, Predictive Survey Material Modeling.

This community bank design scenario requires precise alignment of EWC deployment scale, AAA integration, and traffic routing decisions with the stated constraints. With four APs per campus and a goal of local traffic handling, converting a single C9120 to EWC mode is optimal — converting two APs to EWC (Options B and C) on a four-AP campus wastes 50% of campus AP infrastructure for controller functions rather than client service. The single EWC AP serves as the active local controller for the remaining three client-serving APs. The HQ WLC set as N+1 backup ensures that if the branch EWC fails, the remaining APs fall back to the centralized controller. For the guest WLAN, local web authentication on the guest VLAN provides the locally routed guest access requirement without requiring WAN connectivity to HQ. For the employee WLAN, adding the HQ ISE AAA server to the EWC ' s RADIUS configuration enables 802.1x PEAP authentication to traverse the WAN to ISE at the time of client association. Once authenticated, traffic is locally switched — satisfying both the central authentication and local traffic routing requirements simultaneously. Option D ' s use of guest anchor for the employee WLAN is architecturally incorrect and would route traffic through HQ rather than locally. Reference: WLSD Study Guide — EWC Design, N+1 Redundancy, AAA Integration for Branch WLANs, Local Web Authentication.

To focus the coverage heat map on the desired coverage threshold, the engineer should use the RSSI slider to set the heat map to the desired cutoff filter. This action adjusts the display to show only the signal levels that meet or exceed the specified RSSI value, effectively filtering out weaker signals and highlighting areas with sufficient coverage. In Ekahau and similar survey tools, the RSSI slider provides a dynamic way to set minimum signal thresholds, allowing the engineer to quickly validate whether coverage meets design targets such as -67 dBm for voice or -70 dBm for data. Changing the color scheme (Option A) only modifies the visual representation without filtering data. The RSSI calibration tool (Option B) adjusts how the tool perceives signal levels, not the display filter. Filtering by AP (Option D) would remove APs from the view, potentially hiding coverage gaps. Reference: WLSD Study Guide — Post-Deployment Survey, Ekahau Heat Map Tools, RSSI Coverage Filtering.

Cisco Spectrum Expert is a dedicated spectrum analysis tool designed to identify and analyze non-Wi-Fi interference sources at Layer 1. During a post-deployment site survey, it can detect interference from various devices such as cordless phones, Bluetooth devices, microwave ovens, video cameras, and other unlicensed RF emitters. The tool provides a visual representation of the RF environment across the frequency spectrum, allowing engineers to pinpoint the exact source of interference and characterize it by duty cycle, frequency, and interference pattern. A network analysis module (Option A) operates at Layer 2 and above, unable to detect non-802.11 RF emissions. Wireless intrusion prevention (Option B) detects rogue APs and 802.11 attacks but not Layer 1 RF noise. Wireshark (Option C) is a packet capture tool for Layer 2-7 analysis and cannot detect non-Wi-Fi RF energy. Reference: WLSD Study Guide — Layer 1 Spectrum Analysis, Post-Deployment Survey, Non-Wi-Fi Interference Identification.

On the Cisco Catalyst 9800 IOS XE WLC platform, the tag-based configuration model uses site tags to associate APs with specific profiles including a flex profile and an AP join profile. The site tag is a fundamental binding element — when any component of a site tag is modified, including renaming the flex profile associated with that tag, the WLC treats this as a material configuration change requiring the AP to re-evaluate its operational parameters. Specifically, the AP must disconnect its existing DTLS (Datagram Transport Layer Security) control plane tunnel to the WLC and re-establish it. This DTLS session disconnect and rejoin cycle is equivalent to a full AP rejoin: CAPWAP discovery, DTLS handshake, join request, configuration download, and image verification. Client service is interrupted on the affected AP during this process. Firmware updates (Option A) occur via a separate image download process. Temporary SSID disable (Option B) is not a defined behavior for profile name changes. Switching to a backup controller (Option C) requires AP failover conditions, not configuration changes. Understanding the disruptive nature of site tag modifications is essential for change management in production 9800 deployments. Reference: WLSD Study Guide — Catalyst 9800 Tag-Based Configuration Model, Site Tag Architecture, Flex Profile and AP Join Profile Management.

When Cisco WLCs are configured to use multicast for mobility group communications, all WLCs participating in the same mobility group must be configured with an identical multicast group IP address. The mobility multicast mode allows a WLC to send a single multicast frame received simultaneously by all other WLCs in the group, rather than sending individual unicast copies to each peer. For this to function correctly, every WLC in the group must join the same IP multicast group address, and the underlying network infrastructure must be configured to support IP multicast routing or IGMP snooping for that specific group address. If any WLC is configured with a different multicast IP address, it will join a different multicast group and will not receive mobility messages from the other WLCs, effectively isolating it from the group ' s communication plane. Service port IP addresses (Option A) are unique per controller. Interface IDs (Option B) are locally significant identifiers. Management IP addresses (Option C) are unique per WLC and identify each peer in unicast configurations. Reference: WLSD Study Guide — Mobility Group Configuration, Multicast Mobility Messaging, WLC Peer Communication.

Layer 1 interference analysis is foundational to the Cisco site survey methodology. When a spectrum analyzer reveals periodic noise floor spikes across multiple channels with no clear line-of-sight obstruction, the root cause is almost certainly a non-802.11 device — candidates include cordless phones, video cameras, microwave equipment, or radar systems triggering DFS events. The correct engineering response is systematic documentation: capture the time of occurrence, the specific frequency or frequency range, and the geographic location of the interference signature. This triangulation data enables correlation with physical devices present in the facility. Simply increasing transmit power (Option A) raises the noise floor for neighboring cells and worsens co-channel interference. Using WLC monitoring tools (Option B) is insufficient because the WLC cannot detect non-802.11 energy at Layer 1. Adjusting the channel plan (Option C) without fully characterizing the interferer is premature. Only Option D follows the correct Cisco survey methodology for Layer 1 analysis, leading to actionable AP placement adjustments. Reference: WLSD Study Guide — Wireless Site Survey Methodology, Layer 1 Spectrum Analysis, Interference Identification and Mitigation.

When a data path mobility tunnel fails to come up between WLCs, one of the key troubleshooting steps is to verify whether the necessary ports are open through firewalls in the path. Cisco AireOS mobility tunnels use UDP port 16666 for mobility control traffic and IP Protocol 97 (EtherIP) for mobility data traffic in legacy mode. Establishing a Telnet connection from a local PC to the firewall on port 16666 tests whether the control path port is reachable and not being blocked by the firewall. If the Telnet connection fails, it confirms that the firewall is blocking port 16666, which would prevent the mobility control tunnel from establishing — a prerequisite for the data tunnel. While a Telnet test to port 16666 specifically tests the control path, in practice this is the first verification performed when the data path cannot establish (since the data path depends on the control path being operational). IP Protocol 97 cannot be tested via Telnet (which is TCP). The mping command (Option D, not ' mapping ' ) tests mobility tunnel connectivity from the WLC itself after the tunnel is established. Reference: WLSD Study Guide — Mobility Tunnel Troubleshooting, Firewall Port Requirements, UDP 16666 and IP Protocol 97.

This question hinges on a fundamental network engineering constraint: the maximum transmission distance of copper Ethernet cabling. IEEE 802.3 standards specify a maximum segment length of 100 meters (328 feet) for all standard PoE and Ethernet over Category 5e, 6, or 6A UTP copper cabling. The parking lot light poles are approximately 200 meters from the closest wiring closet — more than double the maximum copper distance. This immediately eliminates Options A and D, which specify Category 6 UTP cabling: at 200 meters, UTP copper cannot reliably carry Ethernet at any supported speed, and PoE cannot be delivered over this distance regardless of standard. The correct solution is fiber optic connectivity between the wiring closet and the parking lot, combined with a local AC/DC power module at each pole location. Fiber optic cabling supports single-mode runs of kilometers and multi-mode runs of hundreds of meters at Gigabit speeds — easily spanning 200 meters. At the AP mounting location on the light pole, an AC/DC power module (powered from the pole ' s existing electrical supply) converts AC power to the DC power the AP requires. Option B (fiber with 802.3af) is incorrect because PoE cannot be delivered over fiber — 802.3af requires copper cabling for simultaneous power and data delivery. Reference: WLSD Study Guide — Outdoor AP Deployment, Fiber vs. Copper Distance Limitations, Outdoor Power Solutions.

This question requires a straightforward PoE power budget calculation. The IEEE 802.3at standard (PoE+) delivers a maximum of 30W at the Power Sourcing Equipment (PSE/switch port). Cisco 9100 Series access points such as the C9120, C9130, and C9136 are designed to operate with full functionality using PoE+ at 30W per AP. The total PoE power requirement for 12 APs is calculated as: 12 APs × 30W per AP = 360W. This figure represents the total power draw that the Cisco 3800 Series PoE+ switch must be capable of supplying across the connected AP ports simultaneously. The Cisco Catalyst 3800 Series switches offer a total PoE power budget that must be validated against this 360W requirement during the design phase. Note that some Cisco 9100 APs support higher power modes through IEEE 802.3bt (PoE++), which can provide up to 90W — but the question specifies PoE+ (802.3at) for the switch infrastructure, making 30W × 12 = 360W the correct answer. Option D (720W) would correspond to 24 APs at 30W each. Option B (1080W) would represent 36 APs. Option C (184.8W) corresponds to a non-standard per-AP power value. Reference: WLSD Study Guide — PoE Power Budget Planning, Cisco 9100 Series AP Power Requirements, Wired Infrastructure Design for Wireless Deployments.

Warehouse wireless deployments present unique RF engineering challenges: extremely high ceilings (often 25-45 feet), dense metallic shelving systems that create specular reflections and RF shadows, narrow aisles between rack systems, and the need to cover linear travel paths for RF scanner devices. The recommended Cisco antenna strategy for warehouses is wall-mounted patch (directional) antennas. Patch antennas provide a forward-facing radiation pattern that can be aimed precisely down warehouse aisles, delivering concentrated RF energy where RF scanners actually operate — in the aisles between shelving — rather than dispersing energy into metallic shelving structures. Wall mounting at intermediate height (typically 10-15 feet on aisle-end walls) places the antenna at a height that aligns the main lobe with the working zone of handheld scanners. Ceiling-mounted omnidirectional antennas (Options A and C) at warehouse ceiling height suffer from excessive path loss to floor-level devices and metal shelving obstructions. Low-gain wall-mounted omnidirectional antennas (Option B) lack the directivity needed to focus energy down specific aisles. Reference: WLSD Study Guide — Warehouse Wireless Design, Antenna Selection and Placement, Industrial RF Environment Considerations.

Cisco 3800 Series APs support IEEE 802.11ac Wave 2, which can deliver throughput exceeding 1 Gbps. Fast Ethernet switches are limited to 100 Mbps per port, creating a severe bottleneck. The two actions that provide maximum support are replacing with mGig switches (Option A) and replacing with gigabit switches with 10G uplinks (Option B). mGig (Multi-Gigabit Ethernet) switches support 2.5G and 5G speeds over existing CAT 6A cabling, allowing the full throughput of 802.11ac Wave 2 APs to be utilized without replacing the existing cable plant. Gigabit switches with 10G uplinks ensure that the access layer can support 1 Gbps per AP port while providing sufficient uplink capacity. Since the existing cabling is already CAT 6A, which supports 10 Gbps over short distances and 5 Gbps over 100 meters, there is no need to replace the wiring (Option D eliminates). The 100-meter distance limitation (Option C) already applies to standard Ethernet and is met by CAT 6A — this is not an action but a constraint check. Option E (55 meters) is only relevant for specific 5GBASE-T configurations and doesn ' t maximize support compared to A and B. Reference: WLSD Study Guide — mGig Infrastructure, 802.11ac Wave 2 Infrastructure Design, Switch Upgrade Planning.

The design requirements — optimized performance, interference avoidance, high-density support, and roaming capability — collectively point to a dual-band strategy using narrow channel widths. For 5 GHz operation (Option A), 20 MHz channels are the correct choice for high-density and campus-scale deployments. The 5 GHz band has significantly more non-overlapping channels compared to 2.4 GHz (up to 24 non-overlapping 20 MHz channels in UNII-1, UNII-2, and UNII-3), enabling a robust channel reuse plan with minimal co-channel interference and excellent roaming cell separation. Wider 5 GHz channels (Options C and E — 80 MHz and 40 MHz) would consume multiple channel blocks, dramatically reducing the number of available non-overlapping channels and increasing co-channel interference in dense deployments. For 2.4 GHz operation (Option B), 20 MHz channels are mandatory — there are only three non-overlapping 20 MHz channels (1, 6, 11) in the 2.4 GHz band. Using 40 MHz channels in 2.4 GHz (Option D) eliminates all non-overlapping channel separation, causing massive co-channel interference and is universally contraindicated in enterprise designs. Reference: WLSD Study Guide — Channel Planning, High-Density Design, Frequency Band Selection.

When eping (EoIP ping) fails between two Cisco Wireless LAN Controllers, it indicates that the data path of the mobility tunnel is blocked. In Cisco AireOS wireless networks, the mobility data path uses IP Protocol 97 (EtherIP — Ethernet-over-IP encapsulation) for tunneling client traffic between the anchor and foreign controllers. This is distinct from the control path, which uses UDP port 16666. When the mobility data path (IP Protocol 97) is blocked by a firewall or ACL between the two controllers ' networks, eping will fail because eping specifically tests the EoIP data encapsulation path. After a power cut, when clients disconnect and attempt to roam between APs on different controllers, the mobility tunnel must be operational for session continuity. If IP Protocol 97 is blocked, the mobility data plane cannot function, causing client disconnections during inter-controller roaming events. The other IP protocols listed (67, 77, 87) are not used for Cisco WLC mobility tunneling. Reference: WLSD Study Guide — Mobility Tunnel Data Path, IP Protocol 97 (EtherIP), eping Command and Troubleshooting.