300-425 Questions and Answers

A centralized wireless architecture is suitable for a college with multiple buildings. It allows for centralized management of WLCs and supports seamless roaming for wireless clients across different APs and controllers.

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For wireless clients to use the 5 GHz band when Client Band Select is enabled, certain conditions must be met. Channel bonding should be enabled on the WLAN to allow for wider channels, providing higher throughput available in the 5 GHz band. The client must receive an RSSI above the minimum threshold set for Band Select to steer them towards the 5 GHz band. Additionally, the client device must be dual-band capable to connect to both 2.4 GHz and 5 GHz bands. Co-channel interference levels and UNII-2 extended channels being enabled offer additional benefits but are not requirements for Band Select functionality. Having 802.11a enabled on WLAN is necessary for any operation on the 5 GHz band but does not specifically relate to ensuring clients use this band under Band Select policies.

References := (CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide Premium Edition and Practice)

In a global mesh deployment, using redundant controllers in the least restrictive regulatory domain ensures the highest number of channels available for backhaul. This design accommodates the varying regulatory constraints of different regions by adhering to the domain with the most lenient channel availability.

To optimize roaming in a wireless network with multiple controllers, it is essential to use the same WLAN name (SSID) across all controllers. This allows clients to roam seamlessly between access points managed by different controllers without having to re-authenticate or experience disconnections1.

 To maintain the same VLAN and IP address for users roaming between APs attached to different WLCs, a mobility group should be created between WLC-A and WLC-B. This allows for inter-controller roaming, where client sessions are maintained across different controllers, ensuring that users can move across the campus without losing connectivity or changing IP addresses.

In a hospital setting, the kitchen is a common source of 2.4 GHz RF noise due to the use of microwave ovens which operate on the same frequency. X-ray radiography equipment, while primarily using higher frequency ranges, can also contribute to RF noise in both the 2.4 GHz and 5 GHz bands due to electronic components and shielding inefficiencies. References: CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide.

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 To ensure the anchored traffic remains up if a single WLC in the high-availability cluster fails, the mobility MAC address for the high-availability cluster should be configured. This allows the APs to recognize the cluster as a single entity, maintaining the CAPWAP tunnel to the anchor WLC in the DMZ even if one of the WLCs in the cluster fails.

 The Cisco 5520 WLC v8.3 requires a base license to use OfficeExtend AP functionality, which allows remote workers to have the same wireless connectivity as they would in an office environment.

For predictive designs, especially for location readiness and interference mitigation, a mid-range power level like 18 mw is often used. It provides a balance between coverage and minimizing interference with other devices and networks.

 Enabling control plane encryption on the wireless controller is crucial for establishing a secure mobility tunnel between the wireless controller and the anchor controller. Control plane encryption ensures that the signaling and management traffic traversing the mobility tunnel is encrypted, providing a secure channel for guest access authentication and authorization processes. This is particularly important when the anchor controller is deployed within a DMZ, as it is exposed to potential external threats. The Cisco Catalyst 9800 Series wireless controller supports control plane security features that can be leveraged to secure the mobility tunnel and ensure the integrity and confidentiality of the control traffic.

Creating a mobility group requires that all Wireless LAN Controllers (WLCs) share the same mobility group name. This allows them to recognize each other as peers and participate in client mobility events. The WLCs must be defined as peers in each other’s static mobility members list to facilitate inter-controller communication and roaming.

 Cisco Spectrum Expert is a tool designed to identify and analyze non-Wi-Fi interference sources. During a post-deployment site survey, it can be used to detect interference from various devices such as cordless phones, Bluetooth devices, microwave ovens, and more. This tool provides a visual representation of the RF environment, allowing engineers to pinpoint the exact source of interference and take appropriate measures to mitigate its impact on the wireless network.

References := Designing Cisco Enterprise Wireless Networks (ENWLSD)

Link Aggregation Group (LAG) allows multiple physical ports to be combined into a single logical channel. In the scenario where only one Cisco 9800-40 WLC is available and high availability is required, LAG can be used to manage port redundancy and perform load balancing between APs transparently. This ensures that if one cable fails, the others can continue to carry the traffic without any perceived downtime

An SNR (Signal-to-Noise Ratio) less than 15 dB within the cell boundary during an AP-on-a-stick survey indicates that there is interference affecting the AP’s signal. This interference could be from another signal source that is reducing the quality of the connection, despite the signal strength being within the acceptable cell boundary of -67 dBm.

The IEEE 802.11k protocol is designed to enable radio resource measurement and neighbor list radio management packets. This protocol allows wireless devices to better understand their radio environment, which in turn supports real-time applications over wireless by enabling devices to make quicker and more informed decisions about roaming

 A fully measured wireless survey requires tools that support the active functioning of the network and allow for physical access to install and measure equipment. A PoE (Power over Ethernet) battery is necessary to power the access point during the survey. The access point itself is essential for broadcasting the signal. A ladder is needed to reach high places for proper access point placement and to measure coverage areas effectively.

The 5 GHz band is recommended for voice over wireless due to its wider channel bandwidths, allowing for higher data rates. Setting the cell boundary at -67 dBm ensures sufficient signal strength for reliable voice communication. References: CCNP Enterprise Wireless Design ENWLSD 300-425 Official Cert Guide.

Receiver Start of Packet Detection Threshold (RxSOP) helps to mitigate high-channel utilization by ignoring rogue APs and other RF interference sources. By adjusting the RxSOP threshold, APs can be made less sensitive to unwanted signals, thus reducing the impact of interference. References: CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide.

The human body can attenuate a wireless signal by approximately 6 dB. This is due to the water content in the human body, which absorbs and reflects radio frequency signals, leading to a reduction in signal strength as it passes through or around a person. This factor is important to consider in wireless network design, especially in environments with high user density.

For high availability pairing of two Cisco WLCs for client SSO, it is essential that both controllers have the same number of licenses to ensure feature parity and seamless failover. Additionally, they must run the same operating system version to avoid compatibility issues during SSO operations.

Voice over wireless roaming is sensitive to delays and interruptions. Full reauthentication, as mentioned in option A, can cause noticeable gaps in a voice conversation because it requires time to re-establish security credentials. This process can interrupt the seamless experience expected in voice communications. Option E is also correct because roaming with only 802.1x authentication indeed requires full reauthentication, which can introduce significant delays affecting voice quality. References: For more detailed information, refer to the CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide.

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 Cisco 3800 Series APs support higher speeds provided by IEEE 802.11ac Wave 2, which Fast Ethernet switches cannot fully support. Replacing them with mGig or gigabit switches with 10G uplinks will ensure the infrastructure can handle the increased data rates. The CAT 6A standard supports these speeds, so there’s no need to replace the wiring if it’s already CAT 6A.

 Interface groups allow for flexible WLAN to VLAN mappings by grouping multiple interfaces into a single entity. This enables a single WLAN to be mapped to multiple VLANs, providing scalability and flexibility in network design. AP groups are used to manage the configuration of multiple APs collectively, allowing for consistent WLAN to VLAN mappings across different APs in separate facilities.

The Catalyst 9300X-48HX switches support PoE, which can power the 9166 APs. To ensure that all APs run with full functionalities, including PoE, the engineer should connect the APs to all available ports on the stack of two Catalyst 9300X-48HX switches. This will provide sufficient power and connectivity for the APs to operate effectively. References: Cisco Catalyst 9300X switch specifications and PoE requirements for 9166 APs.

 Creating AP groups for each location allows for the mapping of specific VLANs to an internal SSID tailored for that area. This approach enables clients to be on different subnets based on their building location within a single controller environment.

https://www.cisco.com/c/en/us/support/docs/wireless-mobility/wireless-vlan/71477-ap-group-vlans-wlc.html

FlexConnect APs must be in a FlexConnect group to support 802.11r Fast Transition (FT). This grouping allows for local authentication and key management, which are necessary for fast roaming methods that improve voice quality and wireless IP phone performance during roaming.

When Client A roams from AP1 on WLC1 to AP2 on WLC2 across different subnets, this is considered a Layer 3 roam. Unlike Layer 2 roaming where the client’s database entry moves with them, in Layer 3 roaming, the client’s database entry is copied to the new controller (WLC2). This ensures continuity of service as Client A transitions between access points managed by different wireless LAN controllers. References := (CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide Premium Edition and Practice)

The ‘tracert’ command is used to test connectivity between members of a mobility group by tracing the path that mobility control packets take over the network. This command helps identify any potential issues with the route that the packets are taking, which could affect the ability of guests to connect to the anchor controller in the DMZ. References := (CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide Premium Edition and Practice)

 When designing a backhaul link, the mesh AP role should be set to ‘bridge’ to enable it to connect separate network segments or extend coverage to remote areas.

 During a client roaming event, the Wireless LAN Controller (WLC) is responsible for communicating the new Layer 2 Endpoint ID (EID) mapping of a wireless supplicant to the fabric domain. The WLC acts as a mobility orchestrator within the Cisco Digital Network Architecture (DNA) to ensure seamless roaming and connectivity. References: Designing Cisco Enterprise Wireless Networks (ENWLSD 300-425)

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In a high availability setup with Cisco 5508 Wireless LAN Controllers, the standby controller can be accessed via the console connection and the service port interface. The console provides direct access, while the service port interface allows for network-based access to the standby unit for management purposes.

In Cisco WLC version 8, the need for separate WPlus licenses has been eliminated as all features that were previously part of the WPlus license are now included in the Base license. This consolidation simplifies licensing management and ensures that customers have access to all necessary features without requiring additional licenses. References := (CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide Premium Edition and Practice)

When a client roams between two access points (APs) that are registered to different controllers with interfaces in the same client subnet, the controllers will exchange mobility control messages over UDP port 16666. This is in accordance with the Designing Cisco Enterprise Wireless Networks (ENWLSD) guidelines. The purpose of these messages is to ensure seamless roaming, where the client’s session and authentication state are transferred from one controller to another without requiring re-authentication or re-association by the client. The mobility control messages facilitate the coordinated transfer of the client database entry from the original controller to the new one, maintaining a consistent experience for the user.

 To predict the number of APs needed to support approximately 300 wireless devices on a new floor with an 802.11ac network, the Demand Settings in the Cisco Prime Infrastructure Planning Tool must be adjusted. This setting allows the planner to specify client density and throughput requirements, which are crucial for determining the correct number of APs.

The Virtual Switching Link (VSL) is essential for communication between the active and standby Wireless LAN Controllers (WLCs) in a Stateful Switch Over (SSO) setup. If the VSL goes down, it can lead to a split-brain scenario where both WLCs assume they are active, causing network disruptions and inconsistencies in client handling. References: Designing Cisco Enterprise Wireless Networks (ENWLSD 300-425) Official Cert Guide.

To support a high density of mobile devices and bond channels in groups of two, the channel width for 802.11a should be set to 40 MHz. Setting the data rates to 24 MB and Mandatory ensures that only APs can send 802.11 management frames at this rate, which helps in managing the airtime fairness. References: CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide.

 Devices that can tolerate at most 100 ms of delay when roaming are typically voice devices. Voice applications are sensitive to delays, and ensuring a maximum of 100 ms delay is a common design criterion for a wireless network supporting voice services. References: Designing Cisco Enterprise Wireless Networks (ENWLSD 300-425)

Typically, a Cisco workgroup bridge can support up to 20 wired client connections. This allows for a reasonable number of devices to be connected while maintaining performance.

For outdoor wireless networks, especially in open areas prone to harsh weather, it’s crucial to install lightning arrestors to protect against electrical surges caused by lightning strikes. Additionally, grounding the antenna cables helps dissipate any electrical charge that could damage the equipment.

For a point-to-multipoint mesh network site survey, configuring the Rx power and Tx power is essential. Rx power will determine the sensitivity of the AP to incoming signals, which is crucial for understanding the reach of each mesh point. Tx power settings will influence the strength of the signals transmitted from the AP, affecting the network’s overall coverage. References: Designing Cisco Enterprise Wireless Networks (ENWLSD 300-425)

Jitter is the variation in time between packets arriving, caused by network congestion, timing drift, or route changes. In a Wi-Fi network designed to support video over Wi-Fi, if video multicast traffic is unreliable despite good coverage, jitter is a key performance metric to investigate. High jitter can cause the video to play erratically, freeze, or have sync issues between video and audio streams

AP Fallback is a feature that allows APs to rejoin their primary controller after they have connected to a secondary controller due to a failure. By enabling AP Fallback on the primary controller, the APs will automatically rejoin it when it becomes available again after a power interruption. This ensures that APs return to their designated primary controller for normal operations.

 Cisco Hyperlocation requires a high degree of accuracy in client location tracking. A recommended cell overlap of 50% ensures that client devices are consistently within the range of multiple access points, which improves location accuracy and reliability. References: CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide.

IEEE 802.11ac Wave 2 APs are backward compatible with 802.11a/n clients, allowing these devices to connect and communicate with the newer APs, albeit at their respective maximum supported speeds.

For optimized roaming across multiple Wireless LAN Controllers (WLCs) with Cisco 8821 phones, configuring mobility groups between WLCs allows for seamless roaming and sharing of security contexts. Additionally, using Cisco Centralized Key Management (CCKM) for authentication reduces the time required for re-authentication during roaming, providing a more efficient transition between access points3

In a medical treatment environment where both data and voice services are required, continuous coverage of -67 dBm from one access point is the minimum requirement. This ensures that there is sufficient signal strength for reliable voice communication, which is critical in medical settings. The -67 dBm threshold is commonly recommended for voice applications to ensure call quality and reliability.

So -67dBm covers both Data & Voice with a single AP

By segmenting the VLAN into smaller subnets and assigning them by location, an engineer can use interface groups. This allows for efficient management of network resources and ensures that clients are connected to the closest subnet, reducing latency and improving performance.

 Optimized roaming is a feature that helps manage the client’s roaming behavior by disassociating clients with a signal strength below a predefined threshold. This feature is designed to prevent clients from sticking to an AP with poor connectivity, which can lead to suboptimal performance. If the BSS Transition Management query is causing the client to roam and the disassociation imminent feature is not enabled, it indicates that optimized roaming is likely enabled, prompting the client to seek a better AP connection.

 Cisco FastLocate technology is part of the Cisco Hyperlocation solution, which enhances location tracking accuracy and refresh rates. Implementing Cisco FastLocate technology can address issues with refresh rates for location updates in a custom mobile app by increasing the number of location data points captured, thus providing more frequent and accurate location updates.

References := AP4800 Hyperlocation Deployment Guide - Cisco

In high-density environments, such as stadiums or auditoriums, APs are often mounted under the seats to provide a controlled cell size with attenuation. This placement helps to manage the RF environment by providing attenuation of 6 dB to 20 dB, which can reduce co-channel interference and improve the user experience by ensuring a strong signal and minimizing noise from other cells.