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

 Mobility groups are created by configuring each Wireless LAN Controller (WLC) to use the same mobility domain name and defining each WLC as a peer in the static mobility members list of every other WLC in the group. This configuration allows WLCs to share information and support seamless roaming for wireless clients across different controllers within the same mobility group.

References := Chapter: Chapter 14 - Configuring Mobility Groups - Cisco

 When collapsing all controllers to a single cluster in a central location, one must consider the availability of channels across different regions. Regulatory domains vary globally, and certain channels allowed in Europe may not be available or legal in other parts of the world. This can affect the consistency of wireless coverage and performance.

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

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.

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.

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 reduce co-channel interference, it’s beneficial to decrease channel bonding, which will increase the number of non-overlapping channels available. Reducing the power of the APs can also help minimize interference by reducing the range of each AP’s signal, thereby reducing the chance of overlap.

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.

 Metal doors cause the most signal attenuation in wireless design due to the properties of metal reflecting and absorbing radio waves, which can significantly reduce signal strength. Unlike materials such as cinder block or glass, metal can create a complete barrier for the signal, leading to a phenomenon known as “Faraday Cage” effect, where the metallic enclosure blocks electromagnetic fields. References: Designing Cisco Enterprise Wireless Networks (ENWLSD 300-425)

Mobility domains and mobility groups are concepts used in Cisco wireless networking to manage client roaming and controller interaction. When Wireless LAN Controllers (WLCs) are part of the same mobility domain, they share a common database, allowing them to communicate and facilitate seamless client roaming. A mobility group is a subset of this domain, where specific WLCs work together more closely to share client context and security credentials. This ensures that when a client roams from one access point (AP) to another across different controllers, the authentication and security context are maintained, allowing for a seamless transition without the need to re-authenticate. The mobility group also manages AP fail-over between controllers, ensuring clients can maintain their connections even if their current AP fails or becomes unreachable.

https://www.cisco.com/c/en/us/td/docs/wireless/controller/8-0/configuration-guide/b_cg80/b_cg80_chapter_010011.html

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

 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)

When conducting site surveys for WLAN upgrades to 802.11n, it’s important to consider AP locations that allow for easy access. This facilitates quick maintenance and upgrades, ensuring minimal downtime and disruption to the network. While aesthetics and power availability are also considerations, the primary focus should be on maintaining the network’s performance and reliability.

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 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.

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

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 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.

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

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

 AP groups allow the mapping of specific WLANs (SSIDs) to distinct VLANs for different locations. This design enables clients to be on different subnets based on their building location without modifying the access points’ mode of operation.

 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.

 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.

The mesh backhaul link uses Advanced Encryption Standard (AES) for encryption. AES is a robust encryption standard that is widely used in various security protocols, including WPA2 and WPA3, to provide a high level of security for wireless communications. It ensures that the data transmitted over the mesh backhaul link is protected against unauthorized access and eavesdropping.

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.

 The concern with existing gigabit uplinked switches providing 802.3at is the output power limitation. 802.11ac Wave 2 APs may require more power than what 802.3at can deliver, especially for features like Multi-User Multiple Input Multiple Output (MU-MIMO). References: CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide.

 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.

 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.

 For a pre-deployment site survey, it’s important to know the AP model to understand the capabilities and coverage pattern of the APs. Additionally, knowing the number of clients helps to design a network that can handle the expected client density.

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

 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.

EoIP (Ethernet over IP) is used for communication between controllers in a guest anchor setup, allowing for seamless roaming. Inter-Controller Roaming Mechanism (IRCM) support is necessary for the controllers to facilitate roaming across different wireless LAN controllers.

 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.

Aggregated Probe Response Optimization should be enabled on the controller to optimize roaming, especially for environments with a high density of Apple OS devices. This feature reduces airtime consumption and overhead by aggregating probe responses, which can improve the roaming experience for the employees.

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)

For a cost-effective high availability deployment in a campus enterprise wireless network with three controllers, the N+1 architecture with Stateful Switch Over (SSO) is recommended. This architecture provides redundancy and allows for seamless failover without service interruption, ensuring that the network remains highly available without the need for a one-to-one controller redundancy, which would be less cost-effective

https://www.cisco.com/c/en/us/td/docs/wireless/technology/hi_avail/N1_High_Availability_Deployment_Guide/N1_HA_Overview.html?

 In an auditorium seating 500 students with laptops, a high-density design model is appropriate. This model focuses on supporting a large number of devices in a concentrated area with sufficient coverage and bandwidth. It involves strategic AP placement, proper channel planning, and capacity planning to ensure all students have reliable wireless access. References: CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide Premium Edition and Practice

https://www.cisco.com/c/dam/en_us/solutions/industries/docs/education/cisco_wlan_design_guide.pdf

To support VoWLAN services and provide roaming recommendations to supported voice clients without impacting non-VoWLAN clients, the feature that should be enabled on the VoWLAN SSID is 802.11k neighbor lists. This feature allows APs to provide information about neighboring APs that are candidates for roaming, which helps clients make better decisions about when and where to roam. References := CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide Premium Edition and Practice

When conducting an outdoor bridge site survey, weather and the Fresnel zone are critical criteria to consider. Weather can affect signal propagation and the reliability of the wireless link, while the Fresnel zone relates to the elliptical area around the line-of-sight path between transceivers, which must be clear of obstacles to ensure a strong signal. References: Designing Cisco Enterprise Wireless Networks (ENWLSD 300-425)

 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.

 For mobility tunneling through a firewall in a Cisco wireless network environment, UDP port 16666 must be open along with IP Protocol number ‘97’, which is used for Encapsulating Security Payload (ESP) traffic typically found in IPsec tunnels. By ensuring these ports are mapped correctly through the firewall, R&D engineers can roam within their department while maintaining a secure mobility tunnel. References := (CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide Premium Edition and Practice)

Guest anchoring requires mobility tunnels to be established between the foreign and anchor WLCs. For these tunnels to function, the firewall must allow specific ports for communication. UDP port 16666 is the port used for mobility traffic in Cisco wireless networks, and if it is not allowed through the firewall, MPING and mobility tunnels will fail. References: CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide Premium Edition and Practice

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.

 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.

 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.

Band Select is a feature on Cisco WLCs that encourages dual-band capable clients to connect to the less congested 5 GHz spectrum. It works by delaying the response to clients’ probes on the 2.4 GHz band, making the 5 GHz band more attractive to the client devices.

 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.

Micro cells with reduced power levels are suitable for environments with a high concentration of wireless clients and multimedia applications, as they help manage interference and allow for better roaming capabilities. References: ENWLSD 300-425 Official Cert Guide.

 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)

For mobility tunnels to come up between WLCs, they need to be part of the same mobility group. If they are configured with different mobility groups, the mobility tunnels will not establish, preventing the WLCs from sharing client, AP, and security information.

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.

https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Mobility/emob41dg/emob41dg-wrapper/ch2_Arch.html

 The wireless architecture described is a centralized deployment. This is characterized by access points distributed across multiple buildings and managed centrally by Wireless LAN Controllers (WLCs). Centralized deployments are common in larger environments like a technology company campus because they allow for centralized management, scalability, and advanced features such as load balancing and fault tolerance.

 In a wireless design that requires bridging wired IP surveillance cameras through a mesh AP, the cameras should connect to the AP operating in Mesh AP mode (MAP). This mode allows the AP to function as part of a wireless mesh network, providing connectivity to wired devices like IP cameras in areas where it’s difficult to run Ethernet cables.

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)

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.

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.

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.