HCIA-WLAN flashcards

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

802.11ac frequency band

802.11ac (Wi-Fi 5) operates only in the 5 GHz band and uses wider channels up to 160 MHz with 256-QAM and MU-MIMO downlink, giving higher throughput than 802.11n.

Non-overlapping 2.4 GHz channels

In the 2.4 GHz band, channels 1, 6, and 11 do not overlap because each 20 MHz channel is spaced 5 MHz apart. They form the standard three-channel reuse plan.

CSMA/CA backoff

A station senses the medium idle for DIFS, chooses a random backoff slot count, decrements while idle, and transmits when the counter reaches zero, reducing collision probability.

Hidden node problem

Two clients can each hear the AP but not each other, so both may transmit simultaneously and collide at the AP. RTS/CTS reservation mitigates this.

WPA2 encryption

WPA2 uses AES with CCMP for encryption and integrity, replacing the weaker TKIP used by WPA. It supports either a pre-shared key or 802.1X authentication.

802.11r fast roaming

Fast BSS transition pre-establishes keys with a target AP before the client moves, shortening reauthentication during roaming and reducing voice or video interruption.

OFDMA in 802.11ax

802.11ax divides a channel into resource units so multiple clients transmit in the same time slot, improving efficiency in dense environments with many small packets.

Beacon frame purpose

An AP periodically broadcasts beacon frames advertising the SSID, supported rates, security capabilities, and timing, letting clients discover and synchronize with the network.

CAPWAP UDP ports

CAPWAP uses UDP 5246 for the control tunnel carrying management messages and UDP 5247 for the data tunnel carrying client traffic when tunnel forwarding is used.

Fit versus Fat AP

A Fit AP needs an AC to receive configuration and is centrally managed. A Fat AP runs standalone with local configuration and is used in small deployments.

DHCP option 43

Option 43 carries the AC IP address in DHCP replies so APs can discover the AC automatically without broadcast, DNS, or static configuration.

PoE 802.3at budget

802.3at (PoE+) supplies about 30 W at the source and roughly 25.5 W at the powered device, needed by high-power multi-radio Wi-Fi 6 access points.

AC AP license limit

An AC manages APs up to its licensed count. When the license is exhausted, additional APs fail to register even if the hardware could support them.

AP registration sequence

The AP boots, gets an IP address by DHCP, discovers the AC address, builds the CAPWAP control tunnel, downloads configuration, and then enables its radios.

CAPWAP source interface

The AC interface whose address APs use for the CAPWAP tunnel. It is usually a loopback or VLAN interface and must be reachable from all APs.

Huawei AP naming suffix

Model suffixes indicate form factor and antenna type, such as indoor versus outdoor or built-in versus external antenna. Always confirm details in the datasheet.

Profile binding chain

On a Huawei AC, regulatory domain, radio, and VAP profiles bind to an AP group or AP. The VAP profile references SSID and security profiles.

VAP profile components

A VAP profile combines an SSID profile, a security profile, and a service VLAN, defining one broadcast SSID instance on the AP radio.

Tunnel forwarding

Client data is encapsulated in CAPWAP and sent to the AC, which forwards it. This centralizes policy but loads the AC and the tunnel path.

Local forwarding

Client data is bridged locally at the AP or access switch while only control traffic goes to the AC, reducing AC load and tunnel latency.

Service VLAN role

The service VLAN in the VAP profile determines the broadcast domain into which client traffic is placed after the AP forwards it.

WPA2-Enterprise setup

Requires a RADIUS server, a shared secret on both AC and server, and a security profile set to WPA2-802.1X so clients authenticate with credentials or certificates.

AP whitelist authentication

The AC can require APs to authenticate by MAC address against a whitelist. An AP not on the list is rejected even if it reaches the AC.

Guest network isolation

Guest SSIDs use a separate service VLAN plus ACLs or traffic profiles on the AC to block access to internal subnets while permitting internet access.

display ap all

An AC command listing managed APs with name, MAC, state, and uptime. State 'fault' usually points to tunnel, license, or authentication problems.

RSSI and SNR targets

Aim for RSSI better than about -65 dBm and SNR above 25 dB for voice. Below roughly -70 dBm, data rates drop and retransmissions rise sharply.

Co-channel interference

Multiple APs on the same channel share airtime and defer to each other, cutting throughput. Fix it by channel planning, power adjustment, and using 5 GHz.

Sticky client

A client stays associated with a distant AP instead of roaming to a closer one, causing low rates. Minimum RSSI or band steering settings can force a move.

CAPWAP tunnel flap

Repeated tunnel up/down events drop all clients on the AP. Check link stability, MTU and fragmentation, DTLS, and AC CPU load.

Authentication failure triage

Before blaming the AP, verify RADIUS server reachability, the shared secret, the client credentials, and that the security profile matches the SSID method.

High retry rate causes

Retries rise with weak signal, interference, too many clients per radio, legacy 802.11b/g clients, or excessive channel width. Check per-station rate and retry counters.

Firmware compatibility check

AC and AP firmware must match the vendor compatibility matrix. Mismatched versions can block AP registration or cause unstable tunnels after an upgrade.