300-425 Designing Cisco Enterprise Wireless Networks (ENWLSD) Questions and Answers

The sticky client issue occurs when a wireless client device clings to a suboptimal access point instead of roaming to a better one with a stronger signal. Enabling Optimize Roaming on the Cisco 9800 Series Wireless Controller can alleviate this issue. This feature prompts clients to roam by disassociating them when their signal strength drops below a threshold, encouraging them to seek a better connection.

In a mobility group design, it is essential that all Wireless LAN Controllers (WLCs) share the same mobility domain name to ensure seamless client mobility and roaming between WLCs. This allows for clients to be recognized across the network and maintain their sessions as they roam. Additionally, when WLCs are in a Stateful Switch Over (SSO) high availability pair, they must use the same virtual IP address to present a single network entity to the wireless clients, ensuring uninterrupted service in the event of a failover.

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.

The Voice Readiness tool within Cisco Prime Infrastructure is designed to assess the wireless network’s ability to support voice services, including VoIP. It evaluates various factors such as signal strength, noise levels, and coverage to ensure that the wireless network can handle the quality of service requirements needed for voice communications.

 When performing a site survey of a large outdoor area, a site survey tool with a GPS module is ideal. The GPS module allows for precise location tracking, which is essential for mapping signal coverage over a large area. This tool can help complete the survey efficiently by automatically recording the location of signal measurements

The survey model described is used for location services, VoIP, data, and video. The placement of APs on exterior walls, building corners, and major turns helps ensure consistent coverage and signal strength for a variety of applications, including precise location tracking and high-quality voice and video communications. References: Designing Cisco Enterprise Wireless Networks (ENWLSD 300-425)

 For a government agency requiring high security between device communications, enabling Mobility Encryption across the network is essential. Mobility Encryption enhances the security of the mobility group by encrypting the traffic exchanged between mobility peers, including AireOS, Cisco IOS-XE controllers, and Cisco 4800 Series APs. This encryption helps to protect against potential eavesdropping and unauthorized access, ensuring that sensitive government data remains confidential during wireless transmission.

 For mobility between two buildings with one controller at each site, CAPWAP data and control traffic must be able to pass between controllers. CAPWAP control messages use UDP port 5246 while CAPWAP data messages use UDP port 5247; therefore, these ports must be open to allow inter-controller communication for seamless mobility. References := (CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide Premium Edition and Practice)

 The protocol that needs to be allowed between the networks where the controllers are installed is IP Protocol 97, which is used for encapsulating IP within IP, often used in network mobility and IP tunneling.

 When configuring Cisco Prime Infrastructure, to represent the impact of a thick glass wall with an attenuation of 2dB on the RF signal, the obstacle that should be placed in the map editor is glass. This is because the material-specific attenuation values are used to model the RF signal’s behavior as it passes through different types of obstacles, and the thick glass wall’s impact is best represented by the glass obstacle in the map editor.

 The connectivity of 802.11a, which operates in the 5 GHz band, is reduced in X-ray rooms primarily due to the increased signal attenuation caused by the lead and other dense materials used in the construction of these rooms to shield against X-ray radiation. These materials effectively block or weaken the radio signals used for wireless communication

portable X-ray machines, sending high-resolution images, sometimes in real time, echography machines, and electrocardiography [ECG] machines). These devices may also use the same spectrum as Wi-Fi but with other protocols and, therefore, become sources of interference for your system.

 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.

 In a high-availability configuration, orphaned APs will join the controller with the lowest percentage of associated Access Points (APs) per license capacity by default. This ensures a balanced distribution of APs across the controllers in the mobility group, optimizing resource utilization and network performance. References: Designing Cisco Enterprise Wireless Networks (ENWLSD 300-425)

When using the Cisco Prime Infrastructure Planning Tool for deploying a Greenfield 802.11n network with data, voice, location awareness, and APs equipped with WSSI modules, selecting ‘Voice’ will ensure that the tool accounts for the additional bandwidth requirements of voice applications which have strict QoS requirements. Choosing ‘Location’ will allow the tool to consider the need for more precise location tracking capabilities which typically require additional APs for triangulation purposes. References := CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide Premium Edition and Practice

 The decision to avoid installing APs directly in offices is likely due to transmit power considerations. Placing APs within offices could lead to excessive coverage for small areas, causing interference with other APs and reducing overall network performance. By placing them in common areas like corridors, engineers can ensure more uniform coverage across larger spaces while managing transmit power more effectively for optimal performance.

Jammers are non-Wi-Fi interferers that can be identified by Metageek Chanalyzer. They intentionally disrupt wireless communications by emitting radio frequencies that interfere with Wi-Fi signals. Chanalyzer is designed to detect such patterns of interference.

https://www.metageek.com/training/resources/wifi-and-non-wifi-interference

For a wireless voice deployment, Cisco recommends that the edge of the cell should have a signal strength of -67 dBm to ensure reliable voice quality and seamless roaming capabilities.

 For supporting hyperlocation, it is recommended that APs be aligned in the same direction. This uniform alignment helps in accurately determining the AP Azimuth, X-Y, and ceiling height information, which is crucial for hyperlocation accuracy and minimizes confusion and user-entered errors.

 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.

In a high-density environment like an auditorium, where APs are in close proximity and a large number of devices are connected, the RF profile is used to adjust the radio frequencies of the APs to minimize co-channel interference. The RF profile allows for the configuration of power levels, channel width, and channel assignment to optimize wireless performance and reduce interference. References: CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide Premium Edition and Practice

: Band Select is a feature on Cisco Wireless LAN Controllers (WLC) that encourages dual-band wireless clients to connect to the less congested 5 GHz band. This helps to balance the client load between 2.4 GHz and 5 GHz and improve overall network performance in high-density environments.

A Patch antenna should be used to provide wireless coverage on the perimeter of a building while minimizing signal leakage. Patch antennas have a directional radiation pattern that can be focused along the perimeter.

https://www.cisco.com/c/en/us/td/docs/routers/connectedgrid/antennas/installing-combined/industrial-routers-and-industrial-wireless-antenna-guide/ANT-MP-INT-OUT-M.html

 VLAN Select is a feature that allows for the assignment of clients to different VLANs based on various criteria, such as user credentials or device type. In a centralized wireless deployment with N+1 high availability, incorporating VLAN Select can ensure that clients maintain consistent IP addressing across failovers, preventing them from being assigned IP addresses from a different subnet.

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.

 Before replacing old APs with IEEE 802.11ac-capable APs, it is crucial to check the software version of the wireless LAN controller. The controller’s firmware must support the newer standards and capabilities of 802.11ac APs. An outdated software version may not support the advanced features and performance enhancements offered by 802.11ac technology, leading to compatibility issues and suboptimal network performance.

 The Cisco Aironet 3800 Series APs support mGig, which allows for higher throughput over existing cabling. However, the maximum cable length that supports 5G operation is limited by the quality of the cable and signal attenuation. Category 5e cabling can support 5G operation up to a length of 130 meters, which is within the acceptable range for maintaining the required signal integrity for 5G speeds.

An active ping survey is used to validate network performance by sending and receiving data packets to measure the 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, ensuring that it operates as expected and meets the required service levels.

References := Configuring Active Surveys – Ekahau Customer Support

 In a historic building where aesthetics are important, using APs with integrated antennas can minimize visual impact as they are often designed to be compact and less conspicuous. Patch antennas are also a good choice as they can be mounted flat against surfaces, blending in with the environment while providing directional coverage.

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)

When conducting a Layer 2 site survey, it is recommended to match the survey to the worst client available. This ensures that the wireless network is designed to provide adequate coverage and performance even for the clients with the poorest capabilities, thereby ensuring a consistent user experience for all devices2.

https://www.cisco.com/c/en/us/support/docs/wireless/5500-series-wireless-controllers/116057-site-survey-guidelines-wlan-00.html

To support high availability, the design must include redundant Wireless LAN Controllers (WLCs) to ensure service continuity in case of a failure. Additionally, having a high availability pair with one WLC holding a valid AP count license ensures that all APs can remain connected and services continue without interruption during failover.

https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/7-5/High_Availability_DG.html#pgfId-44074

The ‘eping’ command is used on Cisco Wireless LAN Controllers to verify that the redundancy peer in a Stateful Switchover (SSO) pair of controllers is up and connected. This command sends ECHO packets to the peer controller to ensure connectivity.

 In environments with high client density, deploying APs for 5 GHz coverage is recommended due to the larger number of non-overlapping channels available, which can support higher data rates and client capacity. Disabling the 2.4 GHz radios on some APs can reduce interference and improve overall network performance.

https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/86/b_Cisco_Wireless_LAN_Controller_Configuration_Best_Practices.html

 Changing the TPC Power Threshold to -65 dBm would generally result in a decrease in the transmit power of APs to maintain a smaller cell size. This helps in reducing interference and improving overall network performance. A lower threshold means the APs reduce their power to ensure the signal does not exceed -65 dBm, leading to decreased signal strength at the client side.

 The design approach should use the 5 GHz frequency band without channel bonding to support 20 MHz channels. This provides a balance between network capacity and interference mitigation.

https://www.cisco.com/c/en/us/support/docs/wireless/4400-series-wireless-lan-controllers/108184-config-802-11n-wlc.html

 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.

 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.

 In a high-density environment where 5 GHz coverage is provided by nine APs, disabling the 2.4 GHz radios on some APs can reduce co-channel interference because the 2.4 GHz band has fewer non-overlapping channels. This approach helps maintain coverage while mitigating interference.

 Large cases of liquid materials can cause higher signal loss compared to dry goods due to the way radio frequency (RF) waves interact with liquid, which can absorb and reflect the signals more than dry materials.

 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.

 When a data path mobility tunnel fails to come up, one of the troubleshooting steps is to check if the necessary ports are open and not being blocked by any firewalls in the path. Since the mobility tunnel uses CAPWAP, which operates on UDP ports 16666 (control path) and 16667 (data path), establishing a Telnet connection to the firewall on port 16666 can help determine if the control path is open and if there are any issues that need to be addressed3.

 LAG-based redundancy is chosen for its ability to provide continuous connectivity as long as one port in the LAG is operational (B), utilize the full bandwidth capacity of all the links in the LAG (E), and allow for the grouping of ports into multiple LAGs for increased redundancy and bandwidth (F). References: CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide.

For accurate location services, it is recommended that each location-ready AP hears at least four other APs at a signal level of -75 dBm or better. This ensures sufficient signal overlap and triangulation accuracy for reliable client location tracking. References: Cisco’s guidelines on wireless network design for location services.

 In an outdoor mesh network designed to cover sports fields, a 5 GHz, 14-dBi patch antenna is suitable for the RAP for backhaul connectivity. The higher gain and directional nature of a patch antenna help in focusing the signal over longer distances and in specific directions, which is ideal for connecting various points in a large outdoor area5.

https://www.cisco.com/c/en/us/products/collateral/wireless/aironet-antennas-accessories/product_data_sheet09186a008008883b.html

 Mobility tunnels between Cisco Wireless LAN Controllers (WLCs) use UDP port 16666 for control messages and UDP port 16667 for data traffic. If EPING is failing, it indicates that the necessary ports are not open. Allowing UDP port 16666 through the firewall would enable the control messages required for establishing the mobility tunnels.

 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)

https://www.cisco.com/c/dam/en/us/td/docs/cloud-systems-management/network-automation-and-management/dna-center/deploy-guide/cisco-dna-center-sd-access-wl-dg.pdf

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.