CWNA flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Wavelength formula

Wavelength in meters equals 300 divided by frequency in MHz, giving about 12.5 cm at 2.4 GHz and about 6 cm at 5 GHz.

Free space path loss

Loss increases 6 dB for each doubling of distance or frequency, expressed as 32.44 + 20log10(distance in km) + 20log10(frequency in MHz).

Decibel power rules

Adding 3 dB doubles power and adding 10 dB multiplies it by ten; subtracting 3 dB halves power and subtracting 10 dB reduces it tenfold.

Noise floor and SNR

SNR equals received signal strength minus the noise floor in dB. Roughly 25 dB SNR is needed to sustain the highest 802.11 data rates.

Isotropic radiator

A theoretical point source radiating equally in all directions, serving as the 0 dBi reference against which real antenna gain is measured.

Antenna gain versus beamwidth

Gain is achieved by focusing RF rather than adding power; higher gain narrows the 3 dB beamwidth, extending range while shrinking the coverage angle.

VSWR

Voltage standing wave ratio measures the impedance match between radio and antenna; below 2:1 is acceptable, below 1.5:1 preferred, and high values reflect power back.

PoE 802.3at

Also called PoE+, it delivers 30 W at the power sourcing equipment and 25.5 W at the powered device, versus 15.4 W and 12.95 W for 802.3af.

CAPWAP ports

Lightweight access points and controllers communicate using UDP 5246 for control and UDP 5247 for data, protected by DTLS encryption.

Split MAC

The AP handles time-sensitive functions such as beacons, acknowledgments, and encryption, while the wireless controller manages association, roaming, and security policy.

AP discovery methods

Access points locate a controller through DHCP option 43, DNS name resolution, Layer 2 or Layer 3 broadcast, or a statically configured controller address.

Cell edge RSSI targets

Design for roughly -67 dBm at the cell edge for voice and -70 dBm for data, maintaining at least 25 dB SNR.

2.4 GHz channel plan

Only channels 1, 6, and 11 are non-overlapping in North America, because each channel occupies about 20 to 22 MHz with just 5 MHz spacing.

Capacity versus coverage design

Coverage designs use few access points at high power; capacity designs use many access points at lower power with smaller cells and denser channel reuse.

802.11i

The amendment defining Robust Security Network and WPA2, using CCMP with AES-128 for encryption and 802.1X for authentication.

802.11k, v, and r

k provides neighbor reports, v provides BSS transition management, and r provides fast BSS transition, all working together to speed up client roaming.

Wi-Fi Alliance role

An industry group that certifies interoperability and owns Wi-Fi CERTIFIED, WPA2, WPA3, and Wi-Fi 6/6E/7 branding; it does not set RF regulations.

802.11w

Defines protected management frames, adding integrity protection to deauthentication and disassociation frames to defeat spoofed disconnect attacks.

BSSID

The 48-bit MAC address of an access point radio that uniquely identifies a basic service set and lets clients distinguish between overlapping SSIDs.

Beacon interval

The default is 100 time units, about 102.4 milliseconds; beacons advertise the SSID, supported rates, capabilities, and security settings.

CSMA/CA

Carrier sense multiple access with collision avoidance: stations wait a DIFS period, select a random backoff, transmit, and then await an acknowledgment.

DTIM interval

The number of beacons between deliveries of buffered broadcast and multicast traffic, determining how often sleeping clients wake to check for frames.

WPA2 CCMP

Uses AES-128 in counter mode with CBC-MAC, replacing the weaknesses of WEP and TKIP; defined by 802.11i and used in both personal and enterprise networks.

4-way handshake

Derives the pairwise transient key from the PMK, both nonces, and the MAC addresses, then installs keys and delivers the group key.

EAP-TLS

A mutual certificate-based EAP method requiring certificates on both the client and the server; generally considered the strongest common EAP type.

WPA3 SAE

Simultaneous Authentication of Equals replaces the PSK handshake with a password-authenticated exchange that resists offline dictionary attacks and provides forward secrecy.

High retry rate

Retry percentages above roughly 10 to 15 suggest interference, low SNR, or hidden nodes rather than congestion alone and warrant investigation.

Sticky client

A client that stays associated with a distant access point instead of roaming; mitigated with 802.11k/v, minimum RSSI, and band steering.

Hidden node problem

Two stations out of range of each other transmit simultaneously to the same access point, causing collisions that RTS/CTS or smaller cells can mitigate.

Predictive survey

A software simulation that models access point placement and coverage using a floor plan, wall attenuation values, and planned AP power settings before installation.

Active versus passive survey

Active surveys associate with access points and measure real throughput and roaming; passive surveys only record beacons and noise without connecting.

AP-on-a-stick survey

A method where an access point is temporarily placed at candidate mounting locations to validate coverage, SNR, and roaming before permanent installation.