Explanation:

Why These Options Are Correct:

B) Traffic passes with one port up:

LAG (Link Aggregation Group) provides redundancy by allowing traffic to flow as long as at least one physical link in the bundle is operational.

Reference: Cisco WLC LAG Configuration Guide.

D) Connects to two separate switches:

LAG supports multi-chassis LAG (MLAG), enabling connections to two independent switches (non-stacked) for higher redundancy.

Reference: Cisco StackWise vs. VSS vs. LAG.

E) Full bandwidth utilization:

LAG combines bandwidth of all links (e.g., 2x1Gbps = 2Gbps), unlike port-based redundancy where only one link is active.

Why Other Options Are Incorrect:

A) Packets sent/received on the same port:

False. LAG uses load balancing (e.g., based on MAC/IP) to distribute traffic across all links.

C) Same port with multiple untagged interfaces:

Irrelevant. LAG operates at Layer 2, not dynamic interfaces (a WLC-specific concept).

F) Multiple LAGs:

False. A WLC supports only one LAG (all ports belong to a single bundle).

Key Takeaways for 300-425 Exam:

LAG provides redundancy, bandwidth aggregation, and multi-switch support.

Port-based redundancy (active/standby) is less efficient (no bandwidth aggregation).

MLAG (e.g., vPC, VSS) is critical for high availability in campus designs.

Explanation:

Why Option D is Correct:

In a Cisco Wireless Mobility Group, the Virtual IP Address must be identical across all controllers to ensure seamless Layer 3 roaming.

This allows clients to maintain the same gateway IP (VIP) when roaming between controllers, preventing session drops.

Reference: Cisco Mobility Groups Documentation.

Why Other Options Are Incorrect:

A) DNS entry tied to VIP:
DNS is irrelevant for roaming—clients communicate directly with the VIP, not a hostname.

B) Unique IP for each WLC:
Controllers must share the same VIP (though their management IPs are unique).

C) DNS Host Name field:
Optional for identification but not required for roaming functionality.

Key Takeaways for 300-425 Exam:
Virtual IP (VIP) must match on all WLCs in the mobility group.

Management IPs are unique per WLC.

VIP ensures Layer 3 roaming by acting as a consistent anchor point.

Explanation:

Why These Options Are Correct:

C) Access point:
A temporary AP is essential to simulate real-world RF coverage and measure signal strength, interference, and throughput. Reference: Cisco Wireless Site Survey Guide.

D) Tall tripod:
Used to mount the AP at ceiling height (typical deployment scenario) for accurate measurements.

F) Ladder:
Required to access elevated locations (e.g., ceilings, walls) to place the AP or survey tools.

Why Other Options Are Incorrect:

A) PoE battery:
Not typically needed—APs are powered via PoE injectors/switches during surveys.

B) Spirit level:
Useful for physical alignment (e.g., directional antennas) but not mandatory for general coverage surveys.

E) Goggles:
Irrelevant to RF measurements (safety goggles are for physical labor, not surveys).

Key Takeaways for 300-425 Exam:

A fully measured survey requires:
AP (to generate/test RF signals).
Tripod/ladder (for proper AP placement).
Tools like spectrum analyzers (not listed here) are also critical for interference checks.

Explanation:

Why These Options Are Correct:

A) Site access:
A pre-deployment survey in a high-security area requires physical access to the building to:

Measure RSSI (-65 dBm target)

. Identify obstructions (e.g., walls, metal structures).

Test AP placement for coverage.

Without access, the survey cannot be performed accurately.

Reference: Cisco Site Survey Security Guidelines.

B) AP model:
The AP’s RF characteristics (e.g., transmit power, antenna gain) directly impact RSSI.

Different models (e.g., Cisco 9120 vs. 9136) have varying coverage patterns.

Reference: Cisco AP Data Sheets.

Why Other Options Are Incorrect:

C) WLC model:
The controller manages APs but doesn’t affect RSSI measurements during a survey.

D) HVAC access:
HVAC systems may cause interference but are not a survey requirement for RSSI.

E) Number of clients:
Client density affects capacity planning, not pre-deployment RSSI targets.

Key Takeaways for 300-425 Exam:
Pre-deployment surveys focus on coverage (RSSI) and AP placement.
Site access and AP model are critical; WLC/client counts are post-survey considerations.

Explanation:

Why These Options Are Correct:

A) Replace switches with mGig switches:
Cisco 3800 Series APs (802.11ac Wave 2) support Multi-Gigabit (mGig) Ethernet (2.5G/5Gbps) to handle high throughput. Fast Ethernet (100Mbps) is insufficient for modern Wi-Fi 5/6 APs.

Reference: Cisco 3800 Series Datasheet.

C) Cable distances ≤100m:
CAT 6A supports 10Gbps up to 100 meters, which is critical for maintaining signal integrity and PoE delivery.

Reference: TIA/EIA-568 CAT 6A Standards.

Why Other Options Are Incorrect:
B) Gigabit switches with 10G uplinks:
Gigabit (1Gbps) is still a bottleneck for 802.11ac Wave 2 APs (which can exceed 1Gbps in aggregate).

D) Replace with CAT-7E:
CAT 6A is sufficient for 10Gbps/100m. CAT-7E offers no practical benefit here.

E) Cable distances ≤55m:
Unnecessarily restrictive. CAT 6A supports full 100m for 10Gbps.

Key Takeaways for 300-425 Exam:
mGig switches (A) are required to maximize 802.11ac Wave 2 performance.
CAT 6A + 100m (C) is the standard for 10Gbps/PoE.
Avoid over-engineering (e.g., CAT-7E) or under-provisioning (e.g., Gigabit-only switches).

Explanation:

Why Option C is Correct:

Band Select is a feature on Cisco Wireless LAN Controllers (WLCs) that steers dual-band clients to 5 GHz by delaying probe responses on the 2.4 GHz band.

This encourages clients to prefer 5 GHz, which has more channels, less interference, and higher throughput—critical for high-density networks.

Reference: Cisco Band Select Documentation.
Why Other Options Are Incorrect:

A) RRM (Radio Resource Management):
Optimizes channel/power settings but does not directly influence client band selection.

B) Cisco Centralized Key Management (CCKM):
Handles fast roaming (802.11r), unrelated to band steering.

D) Load Balancing:
Distributes clients evenly across APs but does not prioritize 5 GHz.

Key Takeaways for 300-425 Exam:

Band Select (C) is the primary tool to shift clients to 5 GHz.

Combine with RRM for optimal channel/power settings in high-density deployments.

Explanation:

Why Option B is Correct:

Packet Error Rate (PER) is the primary indicator of unreliable Wi-Fi multicast traffic.

Unlike unicast, multicast frames in Wi-Fi:

Are sent without ACKs/retries (per 802.11 standards).

Use the lowest basic rate (e.g., 1Mbps), making them vulnerable to interference.

A high PER means dropped video packets, causing buffering or artifacts.

Reference: Cisco Multicast over Wi-Fi Troubleshooting.

Why Other Options Are Less Relevant:

A) Jitter: Affects real-time streams but is symptomatic of PER issues.

C) Throughput: Measures bandwidth, not packet loss.

D) Latency: Critical for interactive video but not the root cause of multicast unreliability.

Key Fixes for Multicast Issues:

Enable IGMP Snooping on the WLC to prune unnecessary multicast traffic.

Adjust basic rates (e.g., set minimum to 12Mbps) to reduce PER.

Convert multicast to unicast (Cisco VideoStream) for reliability.

Explanation:

Why These Options Are Correct:

B) Weather:
Outdoor bridges are exposed to rain, snow, wind, and temperature extremes, which can:

Attenuate RF signals (e.g., rain fade at 5GHz+).

Physically misalign antennas over time.

Reference: Cisco Outdoor Wireless Design Guide.

E) Fresnel Zone:
The elliptical area around the LOS path must be 60% clear of obstructions (trees, buildings) to prevent signal degradation.

Critical for long-distance bridges (>1km).

Reference: Fresnel Zone Calculation.

Why Other Options Are Incorrect:

A) Near-far effect:
Relevant in cellular networks (not point-to-point bridges).

C) Traffic lights:
No impact on RF (unless using visible-light communication!).

D) Power lines:
Only a concern if physically obstructing the path (not a survey criterion).

Key Takeaways for 300-425 Exam:
Weather (B) affects signal reliability and hardware durability.

Explanation:

Why Option D is Correct:

A site survey tool with GPS (e.g., Ekahau Sidekick, AirMagnet Survey Pro) is ideal for large outdoor areas because: GPS auto-maps your position, eliminating manual floor plan measurements.

Tracks survey progress in real-time, ensuring full coverage without gaps.

Saves time by automating data correlation with physical locations.

Reference: Cisco Outdoor Site Survey Best Practices

Why Other Options Are Incorrect:

A/B) Sniffer mode:
Used for interference analysis, not efficient for coverage mapping in large outdoor spaces.

C) APs in GPS mode:
APs don’t use GPS for surveys—GPS is for location tracking in tools.

Key Takeaways for 300-425 Exam:
GPS-enabled tools (D) are mandatory for efficient outdoor surveys.

Sniffer modes (A/B) are for troubleshooting, not coverage mapping.

For 60,000 sq ft, prioritize automation (GPS) over manual methods.

Explanation:

Why Option D is Correct:

The tracert (traceroute) command is used to test network connectivity between devices by displaying the path and measuring transit delays of packets across the network.

In this scenario, it helps verify if mobility control packets can traverse the management interface between mobility group members (e.g., anchor controller in DMZ and internal controllers).

Reference: Cisco Mobility Groups Troubleshooting.

Why Other Options Are Incorrect:

A) show logging:
Displays system logs but does not test live connectivity.

B/C) mapping:
Not a valid Cisco WLC command.

Key Takeaways for 300-425 Exam:
Use tracert (D) to verify routing paths for mobility control packets.

For deeper analysis, combine with ping and debug mobility on the WLC.

Explanation:

Why Option B is Correct:

AP Groups allow you to map specific SSIDs to VLANs/dynamic interfaces on a per-AP basis.

In this scenario, the secondary WLC must replicate the AP Group configuration from the primary WLC to ensure:

Clients receive IPs from the same subnet post-failover.

SSID-to-VLAN mappings remain consistent.

Reference: Cisco AP Groups Configuration Guide.

Why Other Options Are Incorrect:

A) RF Protocol: Manages radio settings, not VLAN/subnet assignments.

C) VLAN Select: Dynamically assigns VLANs per user (requires AAA), not for failover consistency.

D) AAA Override: Assigns VLANs based on user roles, not AP locations.

Key Takeaways for 300-425 Exam:

AP Groups (B) ensure consistent VLAN/subnet mappings during failover.

Critical for N+1 HA designs with multiple SSIDs.

Explanation:

Why These Options Are Correct:

C) UNII-2e Channels:
Expanding to UNII-2e (e.g., channels 100-144) provides additional non-overlapping 5GHz channels, reducing congestion. Reference: FCC 5GHz Band Allocation.

D) Directional Antennas:
Focused coverage reduces cell overlap and co-channel interference (CCI).

Ideal for high-density areas (e.g., auditoriums).

Reference: Cisco Antenna Design Guide.

Why Other Options Are Incorrect:

A) Raise minimum data rate:
Forces clients to disconnect at lower RSSI but doesn’t reduce channel overlap.

B) Increase TX power:
Worsens overlap by enlarging cell sizes.

E) Power saving mode:
Reduces client power usage but no impact on AP channel planning.

Key Takeaways for 300-425 Exam:
UNII-2e (C) adds more channels (DFS required).

Directional antennas (D) shrink coverage where needed.

Avoid increasing TX power (B)—it exacerbates overlap!