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

An RSSI value of -77 dBm is within the range that a 5 GHz radio can receive and decode, provided it’s not below the RX-SOP threshold set for the RF profile. Since the RF profile is set to Medium for 802.11a, which operates in the 5 GHz band, the AP’s 5 GHz radio will decode the frames.

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.

When the mobility tunnel is not operational for the data path, it is essential to validate the network’s firewall settings. Firewall port 16666 must be open to allow mobility control messages to pass through, and firewall IP protocol 97 (EtherIP) must be permitted to enable the encapsulation of IP within IP, which is necessary for the data path of the mobility tunnel. Ensuring these firewall settings are correctly configured is critical for facilitating inter-controller roaming and operational mobility tunnels.

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

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.

References: The official Cisco FlexConnect configuration guide 

To minimize channel utilization and interference with existing tenant networks, it’s best to use the UNII-1 channels, which are typically less congested, and stick to 20-MHz channels to provide more non-overlapping channels and reduce co-channel interference.

 For Stateful Switchover (SSO) to function correctly, the redundancy ports on both the primary and secondary controllers must be directly connected. This allows for the necessary state and configuration information to be synchronized between the two controllers, preventing the secondary controller from entering maintenance mode in the event of a failover.

 Cisco workgroup bridges typically support up to 8 wired clients. With 42 users, each having a computer and a VoIP phone, that’s a total of 84 devices. To connect all devices while keeping costs at a minimum, the company would need 6 APs (as 7 x 12 = 84), with each AP supporting 14 devices (7 computers and 7 VoIP phones).

So, each AP will have 25 clients. Minimum 4 APs are sufficient.

The behavior of guest client sessions in the US being anchored to the WLCs in Europe despite the presence of a local anchor WLC can be explained by the failure and subsequent recovery of the US anchor WLC. During the failure, the guest sessions would have been transferred to the European WLCs. After recovery, if the priority settings were not correctly restored or if the system did not automatically revert back to the local anchor, the sessions would remain anchored to the European WLCs3.

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

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.

 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)

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

In Cisco wireless networks, access points can be configured with failover priorities ranging from 1 to 4, with 1 being the highest priority and 4 being the lowest. An access point with priority 1 is considered critical and will be given preferential treatment in failover situations, ensuring that it reconnects to a backup controller before access points with lower priorities

 The redundancy management heartbeat in Cisco Wireless LAN Controllers (WLCs) running 8.x code in Stateful Switch Over (SSO) mode uses UDP packets for communication. When troubleshooting connectivity issues between two WLCs, it is essential to filter for UDP packets in a packet capture to verify the heartbeat communication. The heartbeat packets are sent on a specific UDP port, and filtering for this port can help isolate the heartbeat traffic from other types of traffic in the capture.

Voice services on a wireless network require a strong and stable signal, as well as low interference and retransmission rates. An RSSI (Received Signal Strength Indicator) of at least -67 dBm is considered the minimum for acceptable voice quality, and -65 dBm is even better, providing a buffer for signal fluctuation. A noise floor of -87 dBm would be too high and could interfere with signal clarity. Retransmission rates should be kept as low as possible; 15% or below is a good target to ensure efficient communication.

References: CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide

 Adjusting the RX-SOP (Receiver Start of Packet Detection Threshold) can help to control cell size by making APs less sensitive to low-level signals, thus requiring clients to be closer to the AP to connect, which can ensure they connect to the nearest AP with the highest data rates.

 The AP fallback feature is designed to allow access points to return to their primary controller after they have connected to a secondary controller due to a failure or connectivity issue with the primary. This setting ensures that once the primary controller is back online, the APs will recognize it and re-establish their connection as per the original network design. This feature is crucial for maintaining the intended controller hierarchy and ensuring seamless wireless network operation.

 In the scenario described, where some APs did not failover to their secondary controller despite having sufficient licenses, the issue likely lies with the configuration of the APs to recognize the secondary controller. Since the controllers are not in a mobility group but have A records for their hostnames in DNS, this suggests that they rely on DNS for AP discovery and failover. If APs are not failing over as expected, it could be due to an incorrect IP address configured for the secondary controller on the AP or within DNS. The exhibit shows that the “Secondary Controller” field has an IP address of “10.42.89.11”, which should be verified against DNS records and actual controller settings to ensure accuracy. References := (CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide Premium Edition and Practice)

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

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.

 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 scenario where a customer has multiple Wireless LAN Controllers (WLCs) running N+1 redundancy with Access Points (APs) equally distributed, the critical APs must have priority in case of a WLC failure. If critical APs remain unregistered during a WLC failure, it indicates that the AP failover priority is not enabled globally on the backup WLC. Enabling AP failover priority ensures that critical APs are given precedence over other APs, allowing them to register with the backup WLC first.

In a mobility group, multiple controllers should be configured with the same virtual IP address to ensure proper roaming. This virtual IP address is used by wireless clients during the roaming process to facilitate seamless mobility between controllers.

 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

 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)

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.

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 9800 Series Wireless Controller uses CAPWAP tunnels to encapsulate and transport both control and data traffic between access points and the controller. This allows for centralized management and control while also enabling efficient data forwarding.

https://www.cisco.com/c/en/us/td/docs/wireless/controller/9800/config-guide/b_wl_16_10_cg/mobility.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.

References:

• CCNP Enterprise Wireless Design ENWLSD 300-425 Official Cert Guide

https://www.cisco.com/en/US/docs/solutions/Enterprise/Mobility/emob30dg/RFDesign.html#wp1000551

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.

The exhibit refers to the Cisco Prime Infrastructure’s planning mode feature, which is a tool used for designing and planning wireless networks. The planning mode allows network administrators to input floor plans and simulate access point placement for optimal coverage. It does not require a special license; it is part of the Cisco Prime Infrastructure’s base functionalities. Planning mode does not necessarily present the recommended number of APs; instead, it allows users to manually place potential APs on a map to predict coverage areas. While synchronization with controllers may enhance functionality, it is not strictly necessary for planning mode to operate.

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

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.

The data path issue between the Cisco Catalyst 9800-CL and AireOS 5520, despite an active control path, is likely due to encrypted mobility being enabled on the AireOS 5520. Encrypted mobility requires both peers to have a matching configuration for encryption, which includes proper certificates and shared secrets. If there’s a mismatch, the control path may be established, but the data path can fail due to the inability to establish an encrypted tunnel.

 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.

 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)

To reduce full authentication requests and optimize roaming, enabling Cisco Centralized Key Management (CCKM) on the voice SSID is effective. CCKM allows for fast re-authentication during roaming, which is beneficial for voice applications. Adding APs to a FlexConnect group helps manage APs in remote branches more efficiently.

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 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.

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.

In Cisco WLC release 8.9, the controller software can scale up to 20 WLCs and 3000 APs within a single RF group. This capability allows the Radio Resource Management (RRM) algorithms to function effectively across a larger network, optimizing the wireless experience by managing the RF environment and resources across multiple controllers and access points.

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.

 For a WLAN design that supports services like internet, email, voice, and database access, a signal strength of -67 dBm is considered good for voice and streaming services. A 25-dB SNR (Signal-to-Noise Ratio) is also desirable for high-quality voice and video applications, and a maximum of 1 percent packet loss is acceptable to ensure reliable connectivity and service quality.

https://www.cisco.com/c/en/us/support/docs/wireless/5500-series-wireless-controllers/116057site-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.

 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

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 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.

References: Designing Cisco Enterprise Wireless Networks (ENWLSD) 300-425 Official Cert Guide

 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.

References: CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide

https://www.cisco.com/c/en/us/td/docs/wireless/technology/mesh/81/design/guide/b_mesh_81/Site_Preparation_and_Planning.html

 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

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

 Smartphones and tablets typically have fewer antennas than laptops, which can affect their signal reception and transmission capabilities. Additionally, they often support lower data rates compared to laptops due to their smaller size and power constraints.

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.

 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

 Cisco Hyperlocation requires a dense deployment of access points for accurate location tracking. Adding more APs than a standard site survey suggests can meet the granular location requirements needed for Hyperlocation services. References: ENWLSD official certification guide.

 In an office environment with cubicles, signal propagation is most commonly affected by absorption. This is because the materials used in cubicle walls, such as fabric and other dense substances, tend to absorb the radio frequency (RF) signals used in WLANs, leading to attenuation.

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.