CWNA-109 Sample Questions & Answers

The key innovation of OFDMA in 802.11ax is the ability to partition a channel into multiple smaller sub-channels called Resource Units (RUs). This allows an AP to transmit to and receive from multiple clients simultaneously, dramatically reducing contention and latency, which is ideal for high-density environments with many clients sending small packets.

802.11n (Wi-Fi 4) was a major leap forward, introducing several key technologies simultaneously. It was the first standard to mandate MIMO (Multiple-Input, Multiple-Output), introduce 40 MHz channel bonding, and utilize 64-QAM modulation to push data rates significantly higher than previous standards.

In a WDS, all four address fields are used. Address 1 is the Receiver Address (RA) - the next-hop AP. Address 2 is the Transmitter Address (TA) - the sending AP. Address 3 is the Destination Address (DA) - the final server. Address 4 is the Source Address (SA) - the original client. This allows the frame to be routed across the wireless backbone while preserving the original source and final destination MACs.

U-APSD, part of WMM-Power Save, is ideal for applications like VoWiFi. It allows the client to sleep between transmissions but can wake up instantly to send voice packets without waiting for a beacon. The AP buffers downlink packets and sends them immediately after receiving an uplink packet from the client, providing both power savings and the low latency required for real-time voice.

When an SSID is hidden, APs do not include the SSID in their Beacon frames and will not respond to a broadcast Probe Request (a request with a null SSID field). The client must be configured with the specific SSID in its profile to send a directed Probe Request. If the client sends a broadcast probe, the APs for the hidden network will ignore it, resulting in no Probe Response.

This statement is false. The NAV is a timer used for virtual carrier sense, not physical. A station sets its NAV timer based on the Duration/ID field it reads in frames transmitted by other stations (like RTS/CTS). It will defer access to the medium until its NAV timer counts down to zero. Physical carrier sense is the separate process of actually listening for RF activity on the channel.

Modern APs (especially 802.11ax) often require 802.3at (PoE+), which provides up to 25.5W at the powered device, whereas 802.3af (PoE) only provides up to 12.95W. Upgrading the switches is the most scalable and manageable long-term solution, providing sufficient power and centralized management without the clutter and potential points of failure of individual injectors or power adapters.

A distributed architecture (also known as local bridging or split-MAC) is ideal for this scenario. The APs are managed by a central controller, but client data traffic is switched directly onto the local branch network. This prevents hair-pinning traffic over the slow WAN link and allows the local WLAN to continue functioning even if the WAN connection to the controller is lost (local survivability).

WPA2-Enterprise relies on the 802.1X framework, which uses a RADIUS server as the Authentication Server to validate user credentials.

After successful authentication and association, the client needs an IP address to communicate on the network, which is typically provided by a DHCP server.

To access network resources by name (e.g., internet websites, internal servers), the client requires DNS to resolve hostnames to IP addresses.

OWE, also known as Wi-Fi Certified Enhanced Open, provides the seamless connection experience of an open network (no password required) but adds a crucial layer of security. It uses an unauthenticated Diffie-Hellman key exchange to establish a unique, encrypted session for each client. This protects users from passive eavesdropping by others on the same network, a major vulnerability of traditional open Wi-Fi networks.