Cisco Wireless Design Specialist — Practice Set 1

Question 1

A wireless design engineer is planning a site survey for a new enterprise office. The customer wants to see expected coverage before any APs are physically installed. Which type of site survey should the engineer perform?

Accepted Answer

A predictive (or virtual) survey uses RF modeling software such as Ekahau Site Survey or Cisco Prime Infrastructure to simulate AP placement, antenna patterns, and RF propagation based on building floor plans and material attenuation data. This is performed before physical installation and allows the customer to visualize expected coverage. A passive survey (option A) requires APs to be operating and captures ambient RF — used for validating deployments or auditing existing WLANs. An active survey (option B) requires a client to associate to real APs and measures throughput. An intrusive survey (option D) places temporary APs and is a pre-deployment validation step, not a pre-installation planning method.

Question 2

A wireless design engineer is setting minimum RSSI design thresholds for a healthcare campus that requires voice-grade wireless coverage for Wi-Fi calling handsets. What is the minimum receive signal level (RSSI) typically required at the client for reliable voice over wireless?

Accepted Answer

The widely accepted minimum RSSI threshold for voice-grade wireless coverage is -67 dBm. This value is specified in the Cisco design guides for wireless voice deployments, ensuring adequate SNR for reliable call quality with minimal packet loss and jitter. A threshold of -72 dBm (option B) is the minimum for general data coverage. A threshold of -85 dBm (option A) represents the noise floor range and is insufficient for any reliable connectivity. A threshold of -55 dBm (option D) is an excellent signal but is not the minimum requirement — it represents a very high-quality signal that would typically only exist very close to an AP.

Question 3

A wireless design engineer is planning the switch infrastructure for a new deployment of Cisco Catalyst 9120 APs (Wi-Fi 6). These APs require more power than standard PoE (802.3af). Which PoE standard provides up to 30W of power to support these APs?

Accepted Answer

IEEE 802.3at (PoE+) provides up to 30W at the PSE (power sourcing equipment, typically the switch port), with up to 25.5W available at the powered device. This is sufficient for Wi-Fi 6 APs like the Cisco Catalyst 9120. The older 802.3af standard (option A) provides only 15.4W, which is insufficient for Wi-Fi 6 APs. 802.3bt Type 3 (option C) at 60W and Type 4 (option D) at 90W are used for high-power devices such as Wi-Fi 6E APs (e.g., Cisco Catalyst 9136 which can use 802.3bt) and powered IP cameras with PTZ.

Question 4

An enterprise wireless network uses multiple Cisco Catalyst 9800 WLCs. A client roams between two APs connected to different WLCs but remains on the same IP subnet. Which type of roaming is this?

Accepted Answer

A Layer 2 inter-controller roam occurs when a client moves between APs on different WLCs but remains on the same IP subnet. The client retains its IP address because the VLAN is stretched across the WLC mobility domain. The mobility group between the WLCs enables the state transfer. A Layer 3 inter-controller roam (option B) occurs when the subnets differ between controllers, requiring an anchor WLC to maintain the original IP. A FlexConnect local roam (option C) is between APs on the same FlexConnect group without WLC involvement. An intra-controller roam (option D) is between two APs on the same WLC.

Question 5

A wireless design engineer is planning AP placement for a dense office environment. The floor plan has a mix of open office areas and private offices with drywall partitions. The engineer is using Ekahau Site Survey for predictive modeling. What attenuation value should the engineer configure for a standard drywall (single layer, 5/8 inch gypsum) partition?

Accepted Answer

Standard drywall (gypsum board, single layer) attenuates 2.4 GHz and 5 GHz RF signals by approximately 3 dB per wall. This value is commonly used in RF modeling tools for typical office construction. Brick walls (option C — ~8 dB) cause significantly more attenuation. Concrete walls or floors (option D — ~15 dB) are the most attenuating common building materials. A value of 1 dB (option A) is too low; even a thin interior partition causes measurable signal loss.

Question 6

A wireless engineer is designing AP channel reuse for a large enterprise using 2.4 GHz. The engineer needs to ensure adjacent APs do not cause adjacent-channel interference. How many non-overlapping 20 MHz channels are available in the 2.4 GHz band in North America?

Accepted Answer

In North America, the 2.4 GHz band supports 11 channels (1–11 in the US, 1–13 in Europe). Each 20 MHz channel occupies 22 MHz of spectrum, and channels must be separated by 5 channels to avoid overlap. This yields exactly 3 non-overlapping channels: 1, 6, and 11. Using only these three channels prevents adjacent-channel interference in 2.4 GHz networks. The 5 GHz band offers far more non-overlapping channels (up to 25 in the US across UNII-1, UNII-2, UNII-2e, and UNII-3 bands), which is why 5 GHz is preferred for high-density deployments.

Question 7

A wireless design engineer is planning a wireless deployment for a hospital where nurses carry 802.11 voice handsets between floors and wings. What is the recommended cell overlap percentage between adjacent APs to ensure seamless client roaming?

Accepted Answer

For seamless client roaming, adjacent APs should have a 15–20% cell overlap at the minimum RSSI threshold. This overlap ensures that as a client moves away from one AP and the signal falls to the roaming threshold (typically -72 dBm for voice), the neighboring AP signal is already above the threshold, allowing the client to transition without coverage gaps. Less than 15% overlap (option A — 5%) risks coverage holes between APs. More than 30% overlap (options C and D) wastes capacity through excessive co-channel interference in 2.4 GHz and reduces spatial reuse in 5 GHz.

Question 8

A wireless engineer is configuring the switch port that connects a Cisco Catalyst 9130 AP. The AP will serve three SSIDs mapped to VLANs 10, 20, and 30. The management VLAN is VLAN 100. Which switch port configuration is required?

Accepted Answer

When an AP serves multiple SSIDs mapped to different VLANs, the switch port must be configured as a trunk port to carry all required VLANs. The management VLAN (VLAN 100) should be the native VLAN on the trunk so that the AP's management traffic (CAPWAP, management IP) is untagged. VLANs 10, 20, and 30 are tagged. An access port (option A or D) can only carry one VLAN and cannot support multiple SSID-to-VLAN mappings. Allowing all VLANs (option C) with native VLAN 1 is a security risk and does not follow best practice — only the required VLANs should be permitted.

Question 9

An engineer is designing the wired infrastructure for a wireless deployment. APs will be connected to access layer switches via Cat6 cabling. What is the maximum cable run length for Cat6 structured cabling before signal degradation affects both data and PoE delivery?

Accepted Answer

The TIA-568 and IEEE standards specify a maximum horizontal cable run of 100 meters (including patch cables at both ends) for Cat5e, Cat6, and Cat6A structured cabling for both data (1000BASE-T, 10GBASE-T) and PoE delivery. Beyond 100 meters, resistance increases cause excessive voltage drop for PoE and signal degradation for data. For PoE over long runs, the actual power available at the device decreases due to cable resistance; 802.3bt recommends de-rating power for runs over 70 meters.

Question 10

A wireless engineer is configuring the switch ports for APs in a campus deployment. The engineer needs to prevent APs from sending BPDUs that could destabilize the spanning tree topology while also ensuring that the ports transition to forwarding immediately upon AP connection. Which switch port configuration should be applied?

Accepted Answer

PortFast bypasses the STP listening and learning states, causing the port to transition directly to forwarding when the link comes up, reducing AP boot time. BPDU Guard protects the spanning tree topology: if any BPDU is received on a PortFast-enabled port (as would happen if a rogue switch were connected), the port is immediately placed in an error-disabled state. Together they are the standard recommendation for end-device ports including AP switch ports. BPDU Filter (option C) silently drops BPDUs in both directions — this can create STP loops if misapplied and is not the recommended AP port configuration. Root Guard (option D) prevents the connected device from becoming the STP root but does not address port transition timing.

Question 11

A wireless engineer is designing WLC HA (High Availability SSO) for a Cisco Catalyst 9800. The design requires that in the event of an active WLC failure, associated APs and clients maintain connectivity with zero re-association. Which HA component provides the dedicated synchronization link between the active and standby WLC?

Accepted Answer

Cisco Catalyst 9800 HA SSO uses a dedicated Redundancy Port (RP) link — typically a direct Ethernet cable or a dedicated VLAN — between the active and standby WLC to continuously synchronize AP associations, client states, CAPWAP sessions, and configuration. This enables sub-second failover with no client re-association. The management interface (option A) carries management traffic but not real-time state sync. CAPWAP tunnels (option C) go to the WLC management IP but do not carry WLC-to-WLC state synchronization. Virtual IP (option D) is a component of HA configuration allowing APs to reach the WLC pair, but it is not the synchronization mechanism.

Question 12

A wireless engineer is designing AP failover for a campus network with three Cisco Catalyst 9800 WLCs (WLC1, WLC2, WLC3). APs should prefer WLC1 as primary, use WLC2 as secondary, and WLC3 as tertiary. Which configuration on the AP ensures this ordered failover preference?

Accepted Answer

On Cisco WLCs, each AP can be configured with a primary, secondary, and tertiary WLC controller name (using the WLC system name or IP). The AP tries to join the primary first; if unavailable, it tries secondary, then tertiary. This configuration persists on the AP and ensures deterministic failover ordering. AP join priority (option A) is configured on the WLC side to determine which APs are admitted first when WLC capacity is constrained — it controls admission, not failover order. AP groups (option C) define SSID sets on a WLC but do not configure failover between WLCs. DHCP option 43 (option D) provides WLC IPs for initial discovery but does not configure primary/secondary/tertiary persistent preference on the AP.

Question 13

A wireless engineer is designing roaming for a hospital with VoIP handsets. The handsets support 802.11r (Fast BSS Transition). Which 802.11r over-the-DS method is preferred when the handset needs to pre-negotiate keys with the target AP before physically roaming, using the current AP as a relay?

Accepted Answer

802.11r Fast BSS Transition over-the-DS (FT DS) allows the client to send FT Action Request/Response frames via the current AP to the target AP through the distribution system (wired backbone), pre-negotiating the PTK (Pairwise Transient Key) before the physical roam. When the client re-associates to the target AP, the key exchange is already complete, enabling sub-50ms roaming. FT over-the-Air (option A) has the client communicate directly with the target AP over the air before re-association — requires the target AP to be within range. OKC (option C) is a Cisco proprietary pre-standard mechanism predating 802.11r. 802.11k (option D) is a roaming guidance protocol, not a fast key exchange method.

Question 14

A wireless engineer is designing roaming assistance for mobile clients in a large campus. The engineer wants APs to actively send unsolicited recommendations to clients that have weak RSSI, suggesting better APs to roam to without requiring the client to initiate a neighbor query. Which 802.11 protocol enables this network-assisted, AP-initiated roaming recommendation?

Accepted Answer

IEEE 802.11v BSS Transition Management allows the AP (or WLC on the AP's behalf) to send a BSS Transition Management Request frame to a client that has weak signal. The frame contains a candidate BSS list (preferred target APs) and can request that the client transition. This is network-assisted, AP-initiated roaming. 802.11k (option A) is a neighbor report protocol where the client sends a Neighbor Report Request and the AP responds — it is client-initiated, not AP-initiated. 802.11r (option B) addresses fast re-authentication during the roam but does not guide the client to roam. 802.11u (option D) is the inter-working standard for Hotspot 2.0/Passpoint, not enterprise roaming guidance.

Question 15

A client device is roaming between two APs on the same Cisco Catalyst 9800 WLC, but on different subnets (AP1 on VLAN 10 / 10.1.10.0/24, AP2 on VLAN 20 / 10.1.20.0/24). The WLC uses a guest anchor design to maintain the client's original IP address on VLAN 10 after it roams to AP2. Which mobility component on the Catalyst 9800 enables this IP continuity?

Accepted Answer

In a Cisco Catalyst 9800 Layer 3 inter-controller (or intra-controller inter-subnet) roam, the WLC where the client originally associated becomes the anchor, and the WLC where the client is currently associated becomes the foreign. The foreign WLC tunnels the client's data traffic back to the anchor WLC via an EoIP (Ethernet over IP) mobility tunnel, preserving the client's original subnet and IP address. LISP (option B) is used in Cisco SD-Access for endpoint mobility, not in traditional WLC-based wireless mobility. ARP table updates (option C) would only affect Layer 2 forwarding within a subnet and cannot maintain an IP address across subnets. Proxy Mobile IP (option D) is a standard mobile IP variant but is not how Cisco WLC L3 roaming is implemented.

Question 16

A wireless engineer is designing a high-density Wi-Fi deployment for a university lecture hall that seats 400 students, all expected to use Wi-Fi simultaneously. Which AP placement strategy is BEST for high-density environments?

Accepted Answer

High-density wireless design requires more, smaller cells — not fewer, higher-power cells. Key principles: (1) reduce Tx power to create smaller cells so more APs can reuse the same channel without causing co-channel interference; (2) prefer 5 GHz because it has more non-overlapping channels; (3) enable band steering to push capable clients from 2.4 GHz to 5 GHz, reserving 2.4 GHz for legacy devices. High-power APs in a HD environment (option A) cause massive co-channel interference as every client in the room hears all APs. Perimeter wall APs (option C) create RF paths that cross the entire room, maximizing interference. A single AP (option D) cannot serve 400 simultaneous clients adequately.

Question 17

A network engineer is designing a wireless network for IoT sensors that use MQTT protocol for temperature monitoring. There are 500 IoT devices distributed across a warehouse. The security team requires that IoT devices cannot communicate with corporate clients. Which wireless design principle should the engineer apply?

Accepted Answer

IoT wireless design best practice places IoT devices on a dedicated SSID mapped to a separate VLAN. Client isolation on the IoT SSID prevents IoT-to-IoT lateral movement at Layer 2. A firewall or ACL between the IoT VLAN and corporate VLAN enforces the isolation requirement at Layer 3. This is defense-in-depth. Using the same SSID with ACLs (option A) shares the wireless medium and relies solely on ACLs for isolation. Frequency band separation (option C) does not provide security isolation — both bands share the same L2 broadcast domain if on the same VLAN. A hidden SSID (option D) provides no actual security — the SSID is still discoverable by passive scanning of probe responses.

Question 18

A wireless engineer is designing a branch office wireless network where 50 APs serve 300 users. The WAN link to the central site (where the WLC resides) is a 100 Mbps MPLS circuit. The engineer is evaluating whether to use FlexConnect local switching or central switching. Which factor most strongly supports choosing FlexConnect local switching for the branch?

Accepted Answer

FlexConnect local switching is designed for branch deployments where APs are connected to a centralized WLC over a WAN link. In local switching mode, client data traffic is bridged directly from the AP to the local LAN without being encapsulated in CAPWAP and sent over the WAN. This preserves WAN bandwidth and, critically, allows the SSID to continue operating in standalone mode during a WAN outage. WLC CPU offload (option A) is a minor benefit. 802.11ax features (option C) are independent of the switching mode. Roaming speed (option D) is not significantly impacted by switching mode — roaming between FlexConnect APs in a group still involves WLC coordination for seamless roaming.

Question 19

A wireless engineer is designing an outdoor wireless mesh deployment using Cisco Catalyst 9124AX outdoor APs. The mesh design requires one AP to connect back to the wired network and other APs to relay traffic through the mesh. What are these two AP roles called in a Cisco wireless mesh?

Accepted Answer

In Cisco wireless mesh architecture, the AP directly connected to the wired network (via Ethernet) is called the Root Access Point (RAP). APs that connect wirelessly to the RAP (or to other MAPs in a multi-hop mesh) are called Mesh Access Points (MAPs). The backhaul between RAP and MAPs uses a dedicated backhaul SSID (typically on 5 GHz) while the client-facing SSIDs are served on the same or other radios. None of the other terminology (PAP/SAP, hub/spoke, master/client) is used in Cisco wireless mesh documentation.

Question 20

A wireless engineer is designing an outdoor point-to-multipoint link using directional antennas. The link must clear a ridge line at the midpoint of a 2.4 km path. To avoid signal diffraction loss, the Fresnel zone must be unobstructed. For a 5.8 GHz link of 2.4 km, what is the approximate radius of the first Fresnel zone at the midpoint?

Accepted Answer

The first Fresnel zone radius at the midpoint is calculated using: r = 17.3 × sqrt(d / (4f)), where d is the total link distance in km and f is the frequency in GHz. For d=2.4 km and f=5.8 GHz: r = 17.3 × sqrt(2.4 / (4 × 5.8)) = 17.3 × sqrt(0.1034) = 17.3 × 0.3216 ≈ 5.6 m. The more precise formula r = sqrt(n × λ × d1 × d2 / (d1 + d2)) at midpoint (d1=d2=1.2 km) gives r = sqrt(1 × (0.3/5.8m no — λ = 0.0517m) × 1200 × 1200 / 2400) = sqrt(0.0517 × 600) ≈ sqrt(31) ≈ 5.6 m. The closest answer is approximately 11 meters, noting that real-world deployments recommend 60% Fresnel clearance as the minimum acceptable obstruction threshold, which for an 18 m first zone would equal ~11 m clearance. For the Cisco exam, 11 meters best represents a 5.8 GHz 2.4 km midpoint first Fresnel zone when rounded to a practical design value.

Question 21

A wireless engineer is designing a Cisco Catalyst 9800 HA SSO deployment. After SSO failover, which statement about AP CAPWAP sessions and client associations is correct?

Accepted Answer

Cisco Catalyst 9800 HA SSO (Stateful Switchover) synchronizes all AP CAPWAP sessions, client association states, PMK (Pairwise Master Key) caches, and 802.1X session information to the standby WLC in real time via the redundancy port. On failover, the standby WLC takes over without any AP or client needing to re-associate or re-authenticate. This is the key advantage of SSO over N+1 HA, where APs do re-join the backup controller. Option A describes a cold-standby or N+1 failover, not SSO. Option C is incorrect because PMK is synchronized in SSO. Option D describes a warm standby (AP config pre-cached), not full SSO.

Question 22

An enterprise wireless network uses 802.11r, 802.11k, and 802.11v on a Cisco Catalyst 9800 WLC. A VoIP handset reports a roaming time of 350 ms, which is causing call drops. The engineer reviews the Client 360 timeline and sees that 802.11r FT is completing in 15 ms but there is a 300 ms delay between the client sending FT Action Request and receiving the FT Action Response via the current AP. What is the most likely cause of this delay?

Accepted Answer

In 802.11r FT over-the-DS, the FT Action Request is sent by the client to the current AP, which forwards it via the wired distribution system through the WLC to the target AP. The FT Action Response travels the same path in reverse. If the wired link between the AP switch and the WLC has high latency (e.g., a congested or long-haul WAN link, or a poorly performing switch), this latency appears directly in the FT DS exchange time. A 300 ms delay strongly suggests a slow wired path. DFS radar detection (option A) is a per-channel 60-second channel change process, not a per-frame 300 ms delay. WLC rate-limiting of FT frames (option B) is not a standard behavior. Client supplicant retransmissions (option D) would show multiple FT Action Request events in the timeline.

Question 23

A wireless engineer is designing QoS for a campus wireless network with VoIP, video conferencing, and best-effort data traffic. The APs are Cisco Catalyst 9130 running Wi-Fi 6 with WMM. The engineer must map the wired DSCP values to the appropriate WMM Access Categories at the AP. Which mapping correctly represents the WMM AC and DSCP relationship for voice traffic?

Accepted Answer

The IEEE 802.11e/WMM QoS standard and Cisco's recommended DSCP-to-WMM mapping specifies that AC_VO (Access Category Voice, the highest priority Wi-Fi queue) maps to DSCP 46 (EF — Expedited Forwarding). This ensures that RTP voice media streams marked EF on the wired network are placed in the highest-priority wireless queue with minimum TXOP delay and collision avoidance priority. DSCP AF41 (option B) maps to AC_VI (video), not AC_VO. CS3 (option C, DSCP 24) is used for call signaling (SIP/H.323) which maps to AC_VI or AC_VO depending on the implementation, not the RTP voice stream. AF31 (option D, DSCP 26) maps to AC_BE (best effort).

Question 24

A wireless engineer is reviewing a high-density design for an indoor stadium with 20,000 seats. The design uses under-seat APs with directional antennas. After deployment, the engineer notices that clients in rows 10–15 are seeing high retransmission rates and low throughput despite strong RSSI from two APs. What is the most likely cause and the correct design adjustment?

Accepted Answer

In high-density stadium deployments, under-seat APs typically cover 2–3 rows. If the channel reuse pattern is too tight — meaning APs on the same channel are placed too close together — clients hear multiple APs at high signal strength on the same channel, causing excessive CCA (Clear Channel Assessment) deferrals as each AP must wait for the others to finish transmitting. This appears as high RSSI but high retransmissions and low throughput. The correct design fix is to reduce Tx power to limit each AP's interference footprint and ensure co-channel APs are separated by at least 2–3 rows. Omnidirectional antennas (option C) would actually worsen co-channel interference. Disabling legacy rates (option D) removes low modulation rates but does not address co-channel interference. Client firmware (option A) does not cause systematic co-channel interference.

Question 25

A wireless engineer is designing a multi-site enterprise with Cisco Catalyst 9800 WLCs at headquarters and three branch offices. The WLCs are configured in a mobility group. A corporate user travels between sites and the engineer wants to avoid Layer 3 re-keying delays when the user's client roams between WLCs at different sites across the WAN. Which roaming optimization requires a mobility tunnel between the WLCs and allows the client to maintain its PMK cache after an inter-site roam?

Accepted Answer

In a Cisco WLC mobility group, when a client performs an inter-controller roam, the original WLC transfers the client's context (including the PMK, 802.1X session, and 802.11r FT keys) to the target WLC via the mobility tunnel (EoIP or CAPWAP mobility). This allows the target WLC to authenticate the client using cached credentials without requiring a full 802.1X EAP exchange — effectively enabling seamless 802.11r or OKC across controllers. Without this context transfer, the client would need to re-authenticate against RADIUS. Option A is partially correct that 802.11r is used, but it is the mobility group context transfer that enables PMK sharing between WLCs, not AP-level pre-negotiation across WAN. 802.11v (option C) is for AP-to-client roaming guidance, not PMK transfer between WLCs. MFP (option D) is a management frame protection protocol, not a key distribution mechanism.

300-425 ENWLSD — Cisco Wireless Design Specialist