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

The requirement for users to retain their VLAN assignment and IP address when roaming between buildings managed by different WLCs is a Layer 3 roaming scenario. In Cisco ' s wireless architecture, IP address preservation across controller boundaries is achieved through inter-controller mobility — specifically the foreign-anchor mobility tunnel mechanism. When a client roams from Building A (WLC-A) to Building B (WLC-B), WLC-B becomes the foreign controller and WLC-A becomes the anchor controller. WLC-B tunnels the client ' s traffic back to WLC-A, allowing the client to retain its original IP address even while physically associated to an AP managed by WLC-B. This requires creating a mobility group between WLC-A and WLC-B with both controllers configured with the same mobility group name — the group name is the trust identifier that permits the mobility tunnel and anchor-foreign relationship to form. An SSO cluster (Option B) creates redundancy between two WLCs operating as one logical entity, not inter-building roaming between independent controllers. 802.11r (Option C) accelerates re-association but does not preserve IP addresses across different Layer 3 subnets. AP groups (Option D) control SSID and VLAN assignments but do not enable inter-controller IP preservation. Reference: WLSD Study Guide — Inter-Controller Mobility, Layer 3 Roaming, IP Address Preservation.

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.

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.

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 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.

For a high-density classroom deployment using 5 GHz with channel bonding in groups of two (40 MHz channels), the correct configuration is to set the channel width for 802.11a (5 GHz) to 40 MHz and set the 24 Mbps data rate to Mandatory. Channel bonding refers to combining two adjacent 20 MHz channels into a single 40 MHz channel, doubling the channel width. Since the requirement specifies 5 GHz operation (where high-density design is appropriate), this must be applied to the 802.11a radio profile, not 802.11b (which operates only on 2.4 GHz). Setting 24 Mbps as Mandatory ensures that APs transmit management frames (beacons, probe responses, and other control frames) only at 24 Mbps — this is how the ' only allow APs to send 802.11 management frames at 24 Mbps ' requirement is implemented. Setting it as Supported (Options B and D) would allow the AP to use lower rates for management frames. Options A and D incorrectly target 802.11b, which does not support 40 MHz channels. Reference: WLSD Study Guide — High-Density WLAN Design, 802.11a Channel Configuration, Data Rate and Channel Width Settings.

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 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.

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.

In outdoor wireless deployments, foliage — particularly dense trees — represents the most significant and variable RF obstruction that engineers must account for during site survey and design. Trees are problematic for multiple compounding reasons: the high water content of living tissue causes signal absorption consistent with the principle that water is an effective absorber of 2.4 GHz and 5 GHz RF energy; the irregular branching structure causes multi-path scattering; and foliage density changes seasonally, meaning signal propagation characteristics measured during winter may differ substantially from summer readings when leaves are fully developed. A fully leafed deciduous tree can attenuate a 5 GHz signal by 6–15 dB depending on density and depth. Wind (Option A) causes only momentary mechanical movement of foliage and is not an obstruction itself. Rain (Option B) causes some absorption at higher frequencies but its effect at 2.4 GHz and 5 GHz in typical conditions is marginal compared to foliage. Poles (Option D) are thin structures with minimal RF impact. Outdoor surveys for university campuses must specifically account for tree locations, canopy density, and seasonal variation. Reference: WLSD Study Guide — Outdoor Wireless Design, Environmental RF Attenuation Factors, Outdoor Site Survey Considerations.