Wireless RF Channel & Power Planning

A wireless network is only as good as its RF (Radio Frequency) design. You can deploy the newest Cisco APs, configure all the right WLANs, and still have a poor user experience if APs are transmitting on overlapping channels, at incorrect power levels, or leaving coverage gaps in critical areas. RF planning is not a one-time task — the wireless environment changes continuously as new APs are deployed by neighbours, microwave ovens and Bluetooth devices cause interference, and the physical environment changes with new walls, furniture, and people.

This lab covers the two fundamental dimensions of RF planning: channel assignment (which frequency channel each AP uses) and transmit power control (how loud each AP broadcasts). It explains why 2.4 GHz requires careful non-overlapping channel assignment while 5 GHz offers far more flexibility, how Cisco's Radio Resource Management (RRM) automates both on a WLC, and how to use the WLC RF dashboard to identify and resolve coverage gaps and interference problems in an operational network.

Before starting, ensure you are familiar with 802.11 wireless standards at 802.11 Standards, frequency band basics at Frequency & Channels, and the Wireless LAN Overview. For WLC fundamentals and AP management, see WLC Getting Started. For multi-AP FlexConnect deployments where RF planning is critical for seamless roaming, see FlexConnect AP Configuration.

1. Channel Planning Fundamentals

Why Channel Overlap Causes Problems

802.11 wireless uses CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) — every device on the same channel must listen before transmitting and back off when the channel is busy. This is fine within a single AP's cell. The problem arises when two nearby APs use the same or adjacent channels:

Interference Type	Cause	Effect	Solution
Co-Channel Interference (CCI)	Two or more APs use the exact same channel in the same area	All APs and their clients share the same CSMA/CA contention domain — throughput is divided equally among all stations. A client can hear a neighbouring AP's transmissions and must wait for them to finish before transmitting. In high-density deployments this is the primary throughput killer	Assign non-overlapping channels to adjacent APs — use a channel reuse pattern. Some CCI is unavoidable in high-density deployments; manage it with RRM and proper cell sizing. See 802.11 Standards.
Adjacent Channel Interference (ACI)	Two nearby APs use channels that are close but not identical (e.g., channels 3 and 6)	The channel overlap causes partial signal bleed — the radios cannot cleanly separate the signals. ACI is worse than CCI because the interfering signal is partially decodable but corrupted, causing retransmissions and errors rather than clean deferral	Never use partially overlapping channels. Use only non-overlapping channel sets: 1/6/11 for 2.4 GHz. Adjacent channel interference cannot be managed — it must be avoided entirely by channel assignment. See Frequency & Channels.

2.4 GHz Channel Layout

The 2.4 GHz band in most countries spans 2.401–2.495 GHz. Each 802.11b/g/n channel is 22 MHz wide but the channels are only 5 MHz apart — they heavily overlap. Only three channels are truly non-overlapping:

  2.4 GHz Channel Frequency Map (22 MHz wide channels, 5 MHz spacing)

  Ch: 1    2    3    4    5    6    7    8    9   10   11   12   13
  GHz:2.412 2.417 2.422 2.427 2.432 2.437 2.442 2.447 2.452 2.457 2.462 2.467 2.472

  ╔════════════════════════╗
  ║  Channel 1  (2.412)   ║─────────────────────────────────────────┐
  ╚════════════════════════╝                                         │ OVERLAP
        ╔════════════════════════╗                                   │
        ║  Channel 2  (2.417)   ║                                   │
        ╚════════════════════════╝                                   │
              ╔════════════════════════╗                            │
              ║  Channel 3  (2.422)   ║                            │
              ╚════════════════════════╝                            │
                    ╔════════════════════════╗                      │
                    ║  Channel 4  (2.427)   ║                      │
                    ╚════════════════════════╝                      │
                          ╔═══════════════════════╗                │
                          ║  Channel 5  (2.432)  ║                │
                          ╚═══════════════════════╝                │
                                ╔════════════════════════╗         │
                                ║  Channel 6  (2.437)   ║─────────┘
                                ╚════════════════════════╝
                                      ...
                                                  ╔════════════════════════╗
                                                  ║  Channel 11 (2.462)   ║
                                                  ╚════════════════════════╝

  NON-OVERLAPPING CHANNELS (US/Canada):  1 — 6 — 11
  NON-OVERLAPPING CHANNELS (Europe):     1 — 5 — 9 — 13  (4-channel plan)
  NON-OVERLAPPING CHANNELS (Japan):      1 — 6 — 11 — 14 (14 is 802.11b only)

  RULE: Adjacent APs must use channels at least 5 apart to avoid overlap.
        Channels 1, 6, and 11 are separated by exactly 5 channels — zero overlap.
        NEVER assign channels 1 and 3, or 6 and 8, to adjacent APs.

2.4 GHz Channel Reuse Pattern — Three-Cell Layout

  Correct 2.4 GHz channel assignment for a multi-AP floor:

        [AP: Ch 1]         [AP: Ch 6]         [AP: Ch 11]
       ╱          ╲       ╱          ╲       ╱           ╲
      ╱  Cell  1   ╲─────╱  Cell  6   ╲─────╱  Cell  11   ╲
      ╲    (Ch 1)  ╱     ╲    (Ch 6)  ╱     ╲    (Ch 11)  ╱
       ╲          ╱       ╲          ╱       ╲            ╱
        ─────────           ─────────           ──────────
              ╲                   ╲
         [AP: Ch 11]         [AP: Ch 1]
        ╱          ╲        ╱          ╲
       ╱  Cell  11  ╲──────╱  Cell  1   ╲
       ╲    (Ch 11) ╱      ╲    (Ch 1)  ╱
        ╲          ╱        ╲          ╱

  The pattern repeats: 1 → 6 → 11 → 1 → 6 → 11
  Each AP's cell overlaps only with APs on different channels.
  Co-channel APs are placed far enough apart that their signals
  are below the interference threshold before reaching each other.

  KEY METRIC: Co-channel APs must be separated such that the
  signal from one AP is at least -85 dBm or weaker at the coverage
  boundary of the adjacent co-channel AP.

5 GHz Channel Layout

The 5 GHz band is far richer than 2.4 GHz — it offers up to 25 non-overlapping 20 MHz channels in the US (more in some regions), and supports channel bonding to 40, 80, and even 160 MHz for 802.11ac/ax. The channels are divided into four UNII (Unlicensed National Information Infrastructure) sub-bands. See 802.11 Standards for full 802.11ac/ax channel bonding specifications:

Sub-Band	Frequency Range	20 MHz Channels	Notes
UNII-1	5.150 – 5.250 GHz	36, 40, 44, 48	Indoor use; lower power — most commonly used for enterprise Wi-Fi; no DFS required
UNII-2A	5.250 – 5.350 GHz	52, 56, 60, 64	DFS (Dynamic Frequency Selection) required — APs must scan for radar before using; 30-second CAC (Channel Availability Check) delay on first use
UNII-2C (Extended)	5.470 – 5.725 GHz	100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140, 144	DFS required; highest power allowed; used for outdoor and long-range links
UNII-3	5.725 – 5.850 GHz	149, 153, 157, 161, 165	No DFS required; outdoor use permitted; commonly used alongside UNII-1

  5 GHz 20 MHz Non-Overlapping Channels (US):

  UNII-1:  [36] [40] [44] [48]
  UNII-2A: [52] [56] [60] [64]
  UNII-2C: [100][104][108][112][116][120][124][128][132][136][140][144]
  UNII-3:  [149][153][157][161][165]

  80 MHz Channel Bonding (802.11ac/ax):
  ┌──────┬──────┬──────┬──────┐   ┌──────┬──────┬──────┬──────┐
  │  36  │  40  │  44  │  48  │   │  52  │  56  │  60  │  64  │
  └──────┴──────┴──────┴──────┘   └──────┴──────┴──────┴──────┘
         80 MHz channel (36–48)          80 MHz channel (52–64)

  ┌──────┬──────┬──────┬──────┐   ┌──────┬──────┬──────┬──────┐
  │ 100  │ 104  │ 108  │ 112  │   │ 149  │ 153  │ 157  │ 161  │
  └──────┴──────┴──────┴──────┘   └──────┴──────┴──────┴──────┘
        80 MHz channel (100–112)        80 MHz channel (149–161)

  IMPORTANT: Wider channels = more throughput per AP
             but FEWER non-overlapping channels total.
  80 MHz bonding reduces 25 non-overlapping 20 MHz channels
  to just 6 non-overlapping 80 MHz channels.
  In high-density environments, use 20 MHz channels to maximise
  the number of non-overlapping cells.

Channel Width Trade-offs

Channel Width	Max Throughput	Non-Overlapping Channels (5 GHz US)	Best For
20 MHz	~150 Mbps per spatial stream (802.11n)	25 channels	High-density environments (conference rooms, warehouses, stadiums) — maximise number of non-overlapping cells
40 MHz	~300 Mbps per spatial stream	12 channels	Moderate density offices — balance between throughput and channel reuse
80 MHz	~867 Mbps per spatial stream (802.11ac)	6 channels	Low-density environments (small offices, home) or specific high-throughput use cases
160 MHz	~1.73 Gbps per spatial stream (802.11ac Wave 2)	2 channels	Niche: single AP point-to-point or very low-density environments with a single AP

Transmit Power Planning

Getting channel assignment right is only half the problem. Transmit power determines the size of each AP's coverage cell. Power that is too high or too low creates predictable problems:

Scenario	Cause	Symptom	Fix
TX Power Too High	AP transmits at maximum power (e.g., 20 dBm / 100 mW)	Large cells overlap heavily — co-channel APs interfere with each other across a larger area. Clients stick to a far AP at low data rate instead of roaming to a closer AP. "Sticky client" problem — client hears the far AP loudly and refuses to roam	Reduce AP TX power to create smaller, more controlled cells. Allow RRM to manage power dynamically (TPC)
TX Power Too Low	AP transmits at minimum power (e.g., 1 dBm / 1.25 mW)	Coverage gaps — areas where no AP signal reaches the client threshold. Clients connect at very low RSSI with high retransmission rates and poor throughput	Increase AP TX power or add additional APs to cover the gap. RRM TPC raises power automatically when it detects a coverage hole
Asymmetric Power	AP transmits at high power but client (phone/laptop) has lower max TX power (typically 15–17 dBm)	Client can hear the AP clearly but the AP cannot hear the client's uplink — one-way communication, high retransmissions, poor throughput despite strong RSSI reading	Size cells so the AP transmits at power comparable to the weakest client device (typically 14–17 dBm). This is sometimes called "power symmetry"

2. Radio Resource Management (RRM) — Architecture

Cisco's Radio Resource Management (RRM) is the WLC feature that automates both channel assignment and transmit power control across all managed APs. RRM continuously monitors the RF environment through neighbour discovery and background scanning, then makes dynamic adjustments to optimise the network. RRM has two primary algorithms:

Algorithm	Full Name	What It Controls	Default Interval
DCA	Dynamic Channel Assignment	Assigns channels to AP radios to minimise co-channel and adjacent-channel interference based on real-time RF measurements from all APs in the RF group	Every 10 minutes (configurable); also runs on AP join and on interference events
TPC	Transmit Power Control	Adjusts each AP's transmit power to create appropriately sized cells — reduces power when APs are densely deployed (avoiding excessive cell overlap) and raises power when coverage holes are detected	Every 10 minutes (configurable)

RRM RF Groups — How APs Coordinate

RRM does not operate on individual APs in isolation. APs that can hear each other form an RF Group. Within an RF Group, one WLC is elected as the RF Group Leader. The leader collects RF measurements from all member APs, runs the DCA and TPC algorithms across the entire group, and pushes channel/power assignments back to every AP. This ensures coordinated decisions across the entire coverage area rather than each AP making independent choices that could conflict:

  RF Group Formation and RRM Decision Flow:

  ┌──────────────────────────────────────────────────────────────┐
  │                    WLC (RF Group Leader)                     │
  │                                                              │
  │  1. Receives RF measurements from all APs in group           │
  │     (RSSI of neighbour APs, interference levels, channel     │
  │      utilisation, client counts, noise floor)                │
  │                                                              │
  │  2. Runs DCA algorithm:                                      │
  │     - Builds interference matrix: which APs hear which       │
  │     - Assigns channels to minimise co-channel interference   │
  │     - Respects configured channel list and DCA sensitivity   │
  │                                                              │
  │  3. Runs TPC algorithm:                                      │
  │     - Checks RSSI of each AP's neighbours                    │
  │     - If neighbours are too loud → reduce TX power           │
  │     - If coverage hole detected → increase TX power          │
  │     - Target: each AP heard by 3 neighbours at -70 dBm       │
  │                                                              │
  │  4. Pushes assignments to all APs                            │
  └──────────────────────────────────────────────────────────────┘
          │              │              │              │
       [AP-1]         [AP-2]         [AP-3]         [AP-4]
    Ch:36  Pwr:4    Ch:40  Pwr:3    Ch:44  Pwr:4   Ch:36  Pwr:3
    (RRM assigned — not manually configured)

RRM Sensitivity Thresholds

DCA sensitivity controls how aggressively RRM reassigns channels. Higher sensitivity means RRM reacts to smaller changes in the RF environment — more frequent channel changes. Lower sensitivity means RRM only changes channels when interference is severe — more stable but potentially sub-optimal in changing RF environments:

DCA Sensitivity Level	Channel Change Threshold	Best For
High	5 dB improvement required to trigger a channel change	Dynamic RF environments (venues, retail) with frequent changes in interference sources
Medium (default)	15 dB improvement required	Most enterprise environments — balances stability with responsiveness
Low	30 dB improvement required	Stable environments where channel changes should be minimised — reduces client disruption from channel reassignment. Recommended for healthcare and critical infrastructure deployments.

3. Step 1 — Configure RRM Global Settings on the WLC

RRM is enabled by default on Cisco WLCs. This step configures the key parameters: which channels DCA is allowed to use, the DCA sensitivity, TPC thresholds, and the RRM interval. Navigate to Wireless → 802.11a/n/ac (or 802.11b/g/n) → RRM → DCA. For WLC initial setup see WLC Getting Started:

  WLC GUI — Wireless → 802.11b/g/n → RRM → DCA
  (2.4 GHz radio band)

  ┌───────────────────────────────────────────────────────┐
  │  DCA Mode:          Automatic  ✅ (let RRM decide)    │
  │                     OR Manual  (you assign channels)  │
  │                                                       │
  │  Interval:          10 minutes  (default — keep this) │
  │  DCA Anchor Time:   0:00 (midnight — initial run)     │
  │                                                       │
  │  Sensitivity:       ● Medium  (default — recommended) │
  │                     ○ High                            │
  │                     ○ Low                             │
  │                                                       │
  │  Channel List (allowed channels for DCA):             │
  │  ✅ Channel 1    ✅ Channel 6    ✅ Channel 11        │
  │  ☐  Channel 2    ☐  Channel 3    ☐  Channel 4        │
  │  ☐  Channel 5    ☐  Channel 7    ☐  Channel 8        │
  │  ☐  Channel 9    ☐  Channel 10                       │
  │  (Only check 1, 6, 11 — never allow partial channels) │
  └───────────────────────────────────────────────────────┘
  [Apply] → [Save Configuration]

Restricting the DCA channel list to channels 1, 6, and 11 prevents RRM from ever assigning a partially overlapping channel to any 2.4 GHz radio. If the full channel list (1–13) were enabled, RRM might mathematically determine that channel 4 causes less interference than channel 1 in a specific scenario — but channel 4 creates adjacent channel interference with both channel 1 and channel 6. Always restrict 2.4 GHz DCA to the three non-overlapping channels. For 5 GHz, enable all desired UNII sub-bands in the DCA channel list. See Frequency & Channels for channel planning background.

  WLC GUI — Wireless → 802.11a/n/ac → RRM → DCA
  (5 GHz radio band)

  ┌───────────────────────────────────────────────────────┐
  │  DCA Mode:       Automatic  ✅                        │
  │  Sensitivity:    Medium                               │
  │                                                       │
  │  Channel Width:  ● 20 MHz  (high-density deployments) │
  │                  ○ 40 MHz                             │
  │                  ○ 80 MHz  (low-density / throughput) │
  │                  ○ best    (RRM chooses width)        │
  │                                                       │
  │  Channel List (example — enterprise UNII-1 + UNII-3): │
  │  ✅ 36  ✅ 40  ✅ 44  ✅ 48  (UNII-1 — no DFS)       │
  │  ☐  52  ☐  56  ☐  60  ☐  64  (UNII-2A — DFS)        │
  │  ✅ 149 ✅ 153 ✅ 157 ✅ 161 ✅ 165  (UNII-3)         │
  │  (Disable DFS channels if APs are near radar sources  │
  │   such as airports, weather stations, military)       │
  └───────────────────────────────────────────────────────┘
  [Apply] → [Save Configuration]

For enterprise indoor deployments, starting with UNII-1 (36–48) and UNII-3 (149–165) gives 8 non-overlapping 20 MHz channels without the DFS complexity. DFS channels (UNII-2A and UNII-2C) add significant coverage but require a 30-second Channel Availability Check (CAC) before use and cause service interruption when radar is detected. Enable DFS channels only after confirming there are no radar sources in the deployment area. For 802.11 standard details including 802.11ac channel bonding, see 802.11 Standards. Log DFS radar events with Syslog Configuration and monitor via show logging.

4. Step 2 — Configure Transmit Power Control (TPC)

TPC automatically adjusts each AP's transmit power to maintain appropriate cell sizing. Navigate to Wireless → 802.11a/n/ac → RRM → TPC:

  WLC GUI — Wireless → 802.11a/n/ac → RRM → TPC
  (repeat for 802.11b/g/n)

  ┌───────────────────────────────────────────────────────┐
  │  TPC Mode:          Automatic  ✅                     │
  │                                                       │
  │  TPC Threshold:     -70 dBm  (default — recommended)  │
  │  ─────────────────────────────────────────────────── │
  │  Target: each AP should hear at least 3 neighbours    │
  │  at -70 dBm or better. TPC adjusts power until       │
  │  this condition is met across all APs.                │
  │                                                       │
  │  Maximum Power:     17 dBm (50 mW)  — recommended cap│
  │  Minimum Power:      4 dBm  (2.5 mW)                 │
  │                                                       │
  │  Power Neighbour Count:  3  (default)                 │
  │  ─────────────────────────────────────────────────── │
  │  Number of neighbours each AP must detect at the      │
  │  TPC threshold RSSI before RRM considers coverage     │
  │  adequate. Increase to 5+ for high-redundancy design. │
  └───────────────────────────────────────────────────────┘
  [Apply] → [Save Configuration]

The TPC Threshold of -70 dBm is the target RSSI at which each AP should be heard by its neighbours. RRM reduces an AP's power when its neighbours are heard more loudly than -70 dBm (cells are too large and overlapping too much). RRM increases an AP's power when fewer than the configured number of neighbours are heard at -70 dBm (potential coverage hole). The Maximum Power cap of 17 dBm matches the typical transmit power of a laptop or phone (~15–17 dBm), maintaining power symmetry and preventing the sticky-client problem caused by high-power APs.

WLC CLI — Configure RRM DCA and TPC

! ══════════════════════════════════════════════════════════
! 2.4 GHz (802.11b/g/n) RRM Configuration
! ══════════════════════════════════════════════════════════

! ── Enable automatic DCA ──────────────────────────────────
(Cisco Controller) >config 802.11b channel global auto

! ── Set DCA interval to 10 minutes ───────────────────────
(Cisco Controller) >config 802.11b channel dca interval 10

! ── Set DCA sensitivity (medium) ─────────────────────────
(Cisco Controller) >config 802.11b channel dca sensitivity medium

! ── Restrict DCA to non-overlapping channels only ────────
(Cisco Controller) >config 802.11b channel dca chan-width-11b 20
(Cisco Controller) >config advanced 802.11b channel add 1
(Cisco Controller) >config advanced 802.11b channel add 6
(Cisco Controller) >config advanced 802.11b channel add 11
! ── Remove any other channels from the allowed list ───────
(Cisco Controller) >config advanced 802.11b channel delete 2
(Cisco Controller) >config advanced 802.11b channel delete 3
(Cisco Controller) >config advanced 802.11b channel delete 4
(Cisco Controller) >config advanced 802.11b channel delete 5

! ── Enable automatic TPC ──────────────────────────────────
(Cisco Controller) >config 802.11b txPower global auto

! ── Set TPC threshold and power range ────────────────────
(Cisco Controller) >config advanced 802.11b tpc-threshold -70
(Cisco Controller) >config 802.11b txPower max 4
! ── Power level 4 = approximately 14–17 dBm on most APs  ─
! ── (power levels are vendor-specific: level 1 = max)    ─

! ══════════════════════════════════════════════════════════
! 5 GHz (802.11a/n/ac) RRM Configuration
! ══════════════════════════════════════════════════════════
(Cisco Controller) >config 802.11a channel global auto
(Cisco Controller) >config 802.11a channel dca interval 10
(Cisco Controller) >config 802.11a channel dca sensitivity medium
(Cisco Controller) >config 802.11a txPower global auto
(Cisco Controller) >config advanced 802.11a tpc-threshold -70

! ── Save configuration ────────────────────────────────────
(Cisco Controller) >save config
Are you sure you want to save? (y/n) y
Configuration saved!

5. Step 3 — Configure RF Groups

RF Groups allow multiple WLCs to coordinate RRM decisions across APs managed by different WLCs in the same physical space. Without RF Group coordination, each WLC's APs make independent channel/power decisions that may create conflicts at the boundaries between WLC coverage areas. Navigate to Wireless → 802.11a/n/ac → RRM → RF Grouping:

  WLC GUI — Wireless → 802.11a/n/ac → RRM → RF Grouping

  ┌───────────────────────────────────────────────────────┐
  │  RF Group Name:     NetsTuts-RF-Group                 │
  │  ─────────────────────────────────────────────────── │
  │  RF Group Mode:     ● Auto  (WLC auto-discovers       │
  │                       neighbours and forms group)     │
  │                     ○ Leader (force this WLC to       │
  │                       be the RF Group Leader)         │
  │                     ○ Off   (disable RF grouping —    │
  │                       single WLC deployments only)    │
  └───────────────────────────────────────────────────────┘
  [Apply] → [Save Configuration]

! ── Set RF Group name (must match on all WLCs in group) ──
(Cisco Controller) >config rf-network name NetsTuts-RF-Group

! ── Verify RF Group formation ─────────────────────────────
(Cisco Controller) >show rf-network summary

RF Network name: NetsTuts-RF-Group
RF Group Leader: 10.0.0.50  (this WLC is the leader)
Member count:    2

RF Group Members:
  WLC IP          WLC Name        Role
  --------------- --------------- ------
  10.0.0.50       WLC-HQ          Leader
  10.0.0.51       WLC-BRANCH      Member

All WLCs in the same physical deployment must share the same RF Group name to coordinate RRM. The RF Group Leader is elected automatically (the WLC with the highest IP address becomes leader, or it can be manually forced). The leader runs DCA and TPC algorithms for all APs across all member WLCs — even APs on the member WLC are assigned channels and power by the leader. This ensures a unified, coherent RF plan across the entire physical space regardless of which WLC manages each AP. For multi-site deployments, also see FlexConnect AP Configuration.

6. Step 4 — Manual Channel and Power Overrides (Per-AP)

While RRM handles most environments well, specific APs may need manual overrides — for example, an AP near a stairwell that must cover the floor below, or an AP near a microwave-dense kitchen that should avoid channel 6. Navigate to Wireless → Access Points → [AP Name] → 802.11a/n/ac (or 802.11b/g/n):

  WLC GUI — Wireless → All APs → NetsTuts-AP-01 → 802.11b/g/n

  ── Radio Settings ───────────────────────────────────────
  ┌───────────────────────────────────────────────────────┐
  │  RF Channel Assignment:                               │
  │    ○ Global (use RRM — default)                       │
  │    ● Custom                                           │
  │      Channel: 11  ← manual override                  │
  │                                                       │
  │  Tx Power Level Assignment:                           │
  │    ○ Global (use RRM — default)                       │
  │    ● Custom                                           │
  │      Power Level: 3  ← manual override               │
  │      (power levels: 1=max, typically 5–7 levels)      │
  └───────────────────────────────────────────────────────┘
  [Apply] → [Save Configuration]

! ── Manual channel override on a specific AP ─────────────
(Cisco Controller) >config 802.11b channel ap NetsTuts-AP-01 11

! ── Manual TX power override on a specific AP ────────────
(Cisco Controller) >config 802.11b txPower ap NetsTuts-AP-01 3

! ── Revert AP to RRM automatic control ───────────────────
(Cisco Controller) >config 802.11b channel ap NetsTuts-AP-01 global
(Cisco Controller) >config 802.11b txPower ap NetsTuts-AP-01 global

When a manual override is set, RRM will not change that AP's channel or power — the override takes full precedence. Use overrides sparingly and document them carefully. An undocumented override that was set during troubleshooting and never reverted is one of the most common causes of persistent RF problems — RRM appears to be running but one AP remains on a channel that causes interference with all its neighbours. The CLI command config ... channel ap [AP] global restores RRM automatic control.

7. Step 5 — Using the WLC RF Dashboard

The RF Dashboard is the primary operational tool for monitoring wireless RF health across all APs. It surfaces RF metrics that are impossible to see from the client or AP perspective alone. Navigate to Monitor → Cisco CleanAir → Air Quality Report or the dedicated RF dashboard at Monitor → Summary → Wireless. For SNMP-based monitoring alongside the RF dashboard, see SNMP v2c/v3 Configuration:

Key RF Metrics on the Dashboard

Metric	What It Measures	Healthy Range	Problem Indicator
Channel Utilisation (%)	Percentage of time the channel is busy (both 802.11 frames and non-802.11 interference)	Below 50% for enterprise, below 30% for voice deployments	Above 70% — channel is congested; clients experience high wait times in CSMA/CA backoff
Interference (%)	Non-802.11 RF energy on the channel (microwave ovens, baby monitors, Bluetooth, radar)	Below 10%	Above 20% — significant non-802.11 interference; identify and eliminate the source. Use Wireshark or a Wi-Fi analyser for deeper packet-level analysis.
Noise Floor (dBm)	Background RF noise level on the channel — lower (more negative) is better	Below -90 dBm (typical indoor)	Above -80 dBm — elevated noise floor reducing effective SNR for all clients
Worst Client RSSI (dBm)	Signal strength of the weakest connected client on each AP	Above -70 dBm for voice; above -75 dBm for data	Below -80 dBm — client is at the edge of coverage; likely experiencing high retransmissions
Tx Retransmit Rate (%)	Percentage of frames that required retransmission	Below 10%	Above 20% — indicates interference, low SNR, or coverage gaps causing frame errors
Client Count	Number of clients associated to each AP	Below 25–30 clients per AP for voice; below 50–75 for data	Above 100 — AP is overloaded; consider adding an AP or enabling band steering to move 2.4 GHz clients to 5 GHz. Use ping tests to assess per-client connectivity.
Coverage Hole Alert	RRM detects that a client's RSSI dropped below the coverage hole threshold (-80 dBm by default) while still associated	Zero alerts	Any alert — the identified area has insufficient AP coverage; add an AP or adjust TX power

Coverage Hole Detection — How RRM Identifies Gaps

  RRM Coverage Hole Detection Algorithm:

  Step 1: AP reports per-client RSSI to WLC every 60 seconds
  ─────────────────────────────────────────────────────────
  NetsTuts-AP-03 reports:
    Client a4:c3:f0:11:22:33  RSSI: -82 dBm  (below -80 threshold)
    Client b8:27:eb:44:55:66  RSSI: -79 dBm  (above threshold)
    Client c0:ee:fb:77:88:99  RSSI: -84 dBm  (below threshold)

  Step 2: WLC counts how many clients are below threshold
  ─────────────────────────────────────────────────────────
  AP-03: 2 of 3 clients below -80 dBm
  Coverage Hole Detection threshold: if > (MinFailed%) clients
  are below the RSSI threshold for > (MinDuration) minutes,
  trigger a coverage hole alert

  Step 3: WLC actions
  ─────────────────────────────────────────────────────────
  ● Generates log entry: %RRM-3-COVERAGE_HOLE_DETECTED AP-03
  ● Increases AP-03 TX power by one level (if below Maximum)
  ● If already at Maximum Power: generates alert in RF dashboard
    → requires physical AP placement review or adding a new AP

WLC CLI — RF Dashboard and RRM Verification Commands

! ── Show current channel and power assigned to each AP ────
(Cisco Controller) >show advanced 802.11a summary

AP Name            MAC Address      Admin  Oper  Width  Txpwr  Channel
-----------------  ---------------  -----  ----  -----  -----  -------
NetsTuts-AP-01     00:1a:2b:3c:4d01 Enab   Up    20     4(17d) 36
NetsTuts-AP-02     00:1a:2b:3c:4d02 Enab   Up    20     4(17d) 40
NetsTuts-AP-03     00:1a:2b:3c:4d03 Enab   Up    20     3(20d) 44
NetsTuts-AP-04     00:1a:2b:3c:4d04 Enab   Up    20     4(17d) 149

! ── Show DCA and TPC configuration ───────────────────────
(Cisco Controller) >show advanced 802.11a channel

Automatic Channel Assignment
  Channel Assignment Mode........................ AUTO
  Channel Update Interval........................ 10 mins
  DCA Sensitivity Level.......................... MEDIUM  (15 dB)
  DCA 802.11n Channel Width...................... 20 MHz
  Channel Assignment Leader...................... 10.0.0.50
  Last Run....................................... 243 seconds ago

  DCA Allowed Channel List....................... 36,40,44,48,52,56,
                                                  60,64,100,104,108,
                                                  149,153,157,161,165

(Cisco Controller) >show advanced 802.11a txpower

Automatic Transmit Power Assignment
  Transmit Power Assignment Mode................. AUTO
  Transmit Power Update Interval................. 10 mins
  Transmit Power Threshold....................... -70 dBm
  Transmit Power Neighbor Count.................. 3
  Min Transmit Power............................. 7 dBm
  Max Transmit Power............................. 17 dBm
  Update In Progress............................. No

! ── Show per-AP RF statistics ─────────────────────────────
(Cisco Controller) >show ap auto-rf 802.11a NetsTuts-AP-01

Number of Slots.................................. 2
AP Name.......................................... NetsTuts-AP-01
MAC Address...................................... 00:1a:2b:3c:4d:01

Slot 1 (5 GHz):
  Current TX Power Level....................... 4 (17 dBm)
  Current Channel.............................. 36
  Channel Bandwidth............................ 20 MHz
  Noise Floor.................................. -93 dBm
  Channel Utilization.......................... 18 %
  Interference.................................  3 %
  Coverage / Overlap..........................: Adequate

  Nearby APs / Neighbour Info:
  AP Name            BSSID              RSSI  Channel
  -----------------  -----------------  ----  -------
  NetsTuts-AP-02     00:1a:2b:3c:4e:02  -68   40
  NetsTuts-AP-03     00:1a:2b:3c:4f:03  -72   44
  NetsTuts-AP-04     00:1a:2b:3c:50:04  -81   149

The show ap auto-rf output is the richest single source of per-AP RF information — it shows the current channel and TX power assigned by RRM, the noise floor, channel utilisation, interference percentage, and the full neighbour table with RSSI values. Neighbour RSSI values above -70 dBm indicate good coverage overlap and fast roaming conditions. Values below -80 dBm between adjacent APs may indicate coverage gaps where a client in that area would fall below acceptable signal levels. Correlate with show logging to review RRM coverage hole and DFS event history.

show advanced 802.11a coverage — Coverage Hole Summary

(Cisco Controller) >show advanced 802.11a coverage

Coverage Hole Detection:
  Coverage Hole Detection Mode................... Enabled
  Coverage Voice Packet Count.................... 100 packets
  Coverage Voice Packet Percentage............... 50%
  Coverage Voice RSSI Threshold.................. -80 dBm
  Coverage Data Packet Count..................... 50 packets
  Coverage Data Packet Percentage................ 50%
  Coverage Data RSSI Threshold................... -80 dBm
  Global Coverage Exception Level................ 25%
  Global Client Minimum Exception Level.......... 3 clients

Coverage Hole alerts (last 24 hours):
  AP Name          Radio  Hole Count  Last Event
  ---------------  -----  ----------  -------------------
  NetsTuts-AP-03   5 GHz  12          2024-10-15 14:32:01
  NetsTuts-AP-07   2.4GHz  3          2024-10-15 09:15:44

Coverage hole alerts on NetsTuts-AP-03 (12 events in 24 hours) indicate a persistent coverage problem near that AP — multiple clients are consistently falling below -80 dBm signal strength. This is a physical design issue: RRM has already increased the AP's TX power to the maximum and the problem persists. The resolution requires either repositioning the AP, adding a new AP to fill the gap, or removing physical obstructions. A single AP with frequent coverage hole alerts is almost always an AP placement problem, not a configuration problem. Verify after changes using ping tests from client devices in the affected area.

Identifying Coverage Gaps — RF Dashboard Workflow

Step	WLC Location	What to Look For	Action if Problem Found
1. Check overall RF health	Monitor → Summary → RF Dashboard	Any APs with red/yellow indicators — high channel utilisation, interference, or coverage hole alerts	Drill down to specific APs flagged in the dashboard
2. Identify problem APs	Monitor → Access Points → [AP] → Performance	Channel utilisation above 50%, interference above 20%, noise floor above -85 dBm, worst client RSSI below -75 dBm	Run `show ap auto-rf 802.11a [AP-Name]` for detailed RF data
3. Review neighbour table	`show ap auto-rf [band] [AP-Name]`	Neighbouring APs with RSSI below -80 dBm — gap between AP cells. Fewer than 3 neighbours visible — isolated AP	If gap confirmed, add an AP or increase TX power on surrounding APs
4. Check coverage hole alerts	`show advanced 802.11a coverage`	APs with repeated coverage hole events — RRM already at max power and still detecting holes	Physical AP placement review required — no amount of power increase can fix a placement problem
5. Verify channel assignments	`show advanced 802.11b summary`	Adjacent APs with the same channel (co-channel) or partially overlapping channels (adjacent-channel, 2.4 GHz only)	Check DCA channel list is restricted to 1/6/11 for 2.4 GHz. Run `config 802.11b channel global once` to force an immediate DCA recalculation

Verification Command Summary

Command	What It Shows	Primary Use
`show advanced 802.11a summary`	All 5 GHz AP radios — current channel, TX power level, channel width, admin/oper state	Quick overview of RRM-assigned channels and power levels across all APs
`show advanced 802.11b summary`	All 2.4 GHz AP radios — same as above for 2.4 GHz band	Verify all 2.4 GHz radios are on channels 1, 6, or 11 only
`show advanced 802.11a channel`	DCA configuration — mode, interval, sensitivity, channel list, last run time, RF Group leader	Confirm DCA is in automatic mode with the correct channel list and sensitivity
`show advanced 802.11a txpower`	TPC configuration — mode, threshold, min/max power, neighbour count, update interval	Confirm TPC is automatic with correct threshold (-70 dBm) and power bounds
`show ap auto-rf 802.11a [AP]`	Per-AP RF detail — channel, TX power, noise floor, channel utilisation, interference, neighbour table with RSSI	Deep-dive on a specific AP — identify interference sources, coverage gaps, and channel efficiency
`show advanced 802.11a coverage`	Coverage hole detection settings and per-AP coverage hole alert history	Identify APs with persistent coverage holes that RRM cannot resolve with power adjustment alone
`show rf-network summary`	RF Group name, leader WLC IP, member WLC list	Confirm RF Group is formed correctly with all WLCs participating in coordinated RRM
`show 802.11a cleanair air-quality summary`	CleanAir Air Quality Index (AQI) per AP — composite score of interference type and severity	Identify non-802.11 interference sources such as microwave ovens, video cameras, or Bluetooth — CleanAir classifies and locates the interferer type

8. Troubleshooting RF Channel and Power Issues

Problem	Symptom	Cause	Fix
All 2.4 GHz APs assigned the same channel	`show advanced 802.11b summary` shows all APs on channel 6 — RRM is not distributing channels	DCA channel list is restricted to a single channel (e.g., only channel 6 is enabled), or DCA mode is set to Manual with a static channel assignment	Navigate to Wireless → 802.11b/g/n → RRM → DCA — confirm at least channels 1, 6, and 11 are all checked in the allowed channel list. Confirm DCA Mode is set to Automatic, not Manual. Run `config 802.11b channel global once` to trigger an immediate DCA run
RRM assigning partially overlapping 2.4 GHz channels	`show advanced 802.11b summary` shows adjacent APs on channels 3 and 8 — adjacent channel interference causing retransmissions	The DCA channel list includes channels other than 1, 6, and 11 — RRM is allowed to use all 11 channels and is making mathematically optimal but practically incorrect assignments	Remove all 2.4 GHz channels except 1, 6, and 11 from the DCA allowed list. In the WLC GUI: Wireless → 802.11b/g/n → RRM → DCA — uncheck all channels except 1, 6, 11. Force a DCA recalculation: `config 802.11b channel global once`
APs transmitting at maximum power (sticky client problem)	Clients hold connections to far APs at low RSSI (-75 to -85 dBm) and low data rates instead of roaming to a closer AP. `show advanced 802.11a txpower` shows APs at power level 1 (maximum)	TPC Maximum Power is set too high, or TPC is in Manual mode with a high static power level. High-power cells overlap so much that a client at the edge of AP-A's range still hears AP-A louder than AP-B even when physically closer to AP-B	Cap Maximum Power to 17 dBm (power level 3 or 4 on most Cisco APs). Enable TPC Automatic mode. Consider enabling Optimised Roaming or 802.11r/k/v to actively encourage clients to roam. Verify TPC threshold is set to -70 dBm
Coverage hole alerts despite APs at maximum power	`show advanced 802.11a coverage` shows repeated coverage hole events on a specific AP — alert count increasing daily. RRM has already set the AP to maximum TX power	Physical coverage gap — the AP is not positioned to cover the area, or the area is obstructed by metal, concrete, or RF-absorbing materials. No amount of power increase can overcome a physical placement problem	Conduct a physical walkthrough with a Wi-Fi analyser app (Ekahau, NetSpot) to map signal levels. Reposition the existing AP closer to the coverage gap, or add a new AP to fill it. Review structural obstructions — consider a directional antenna if the AP cannot be relocated
High channel utilisation on 2.4 GHz despite correct channel plan	Channel utilisation above 70% on 2.4 GHz APs even with proper 1/6/11 assignment and only 20–30 clients per AP	Non-802.11 interference from microwave ovens, baby monitors, ZigBee, or Bluetooth devices operating in the 2.4 GHz ISM band. These devices are not 802.11 and do not obey CSMA/CA — they transmit regardless of channel activity	Use `show 802.11b cleanair air-quality summary` and the WLC CleanAir dashboard to identify interference type and location. If non-802.11 interference is confirmed, eliminate the source if possible. If unavoidable (e.g., kitchen microwave), disable 2.4 GHz on nearby APs and rely on 5 GHz coverage for that area. Enable Band Steering to move dual-band clients to 5 GHz
5 GHz AP reboots and comes back on a different channel	An AP that was on channel 100 comes back after a reboot on channel 36 — DFS event triggered a channel change mid-session, dropping all clients	The AP detected radar on a DFS channel (UNII-2A or UNII-2C) and was required by regulatory rules to vacate the channel within 10 seconds. This is normal regulatory behaviour — not a bug	If DFS events are frequent in the deployment area, remove DFS channels from the DCA allowed list: use only UNII-1 (36–48) and UNII-3 (149–165). These channels require no DFS and provide 8 non-overlapping 20 MHz channels. Only enable DFS channels if the additional capacity is required and radar is confirmed to be absent. Log DFS events with `show logging` and forward them to a central syslog server.

Key Points & Exam Tips

The 2.4 GHz band has only three non-overlapping channels in the US: 1, 6, and 11. Adjacent APs must use one of these three channels — never use partially overlapping channels (e.g., 1 and 4, or 6 and 9). Adjacent Channel Interference (ACI) is worse than Co-Channel Interference (CCI) because partially overlapping signals cause uncorrectable corruption rather than clean deferral. See Frequency & Channels.
The 5 GHz band offers up to 25 non-overlapping 20 MHz channels in the US across four UNII sub-bands. Channels in UNII-2A and UNII-2C require DFS (Dynamic Frequency Selection) — APs must detect and vacate the channel when radar is detected. UNII-1 (36–48) and UNII-3 (149–165) require no DFS and are preferred for enterprise deployments. See 802.11 Standards.
Wider channel bonding (40/80/160 MHz) increases throughput per AP but reduces the total number of non-overlapping channels. In high-density deployments, use 20 MHz channels to maximise the number of separate RF cells. In low-density deployments, use 80 MHz for maximum throughput.
Cisco's Radio Resource Management (RRM) automates channel and power assignment via two algorithms: DCA (Dynamic Channel Assignment) selects channels to minimise interference, and TPC (Transmit Power Control) adjusts TX power to create appropriately sized cells. Both run on a configurable interval (default 10 minutes). For WLC setup, see WLC Getting Started.
RF Groups allow multiple WLCs to coordinate RRM across a shared physical space. One WLC is elected RF Group Leader and makes all DCA/TPC decisions for every AP in the group. All WLCs must share the same RF Group name (config rf-network name [name]).
Restrict the DCA channel list for 2.4 GHz to only channels 1, 6, and 11. If the full channel list is enabled, RRM may assign partially overlapping channels that cause ACI. This is the most common RRM misconfiguration in production deployments.
The TPC maximum power cap should match the typical client transmit power (~17 dBm) to maintain power symmetry. High AP TX power causes the sticky-client problem — clients at the edge of a cell hear the far AP strongly and refuse to roam to a closer AP.
The coverage hole detection threshold (default -80 dBm) triggers when a configured percentage of clients fall below the threshold RSSI. RRM automatically increases the AP's TX power in response. If the AP is already at maximum power and holes persist, the problem requires physical AP repositioning or adding a new AP — no configuration change can fix a placement problem.
Use show ap auto-rf 802.11a [AP-Name] for per-AP RF analysis — it shows current channel, TX power, noise floor, channel utilisation, interference percentage, and the neighbour table. Use show advanced 802.11a coverage to view coverage hole alert history. Use show 802.11a cleanair air-quality summary to identify non-802.11 interference sources. Log events with show logging.
On the exam: know the 2.4 GHz non-overlapping channels (1, 6, 11), the difference between CCI and ACI (ACI is worse), the two RRM algorithms (DCA for channels, TPC for power), the TPC threshold target (-70 dBm by default), and the purpose of RF Groups (cross-WLC RRM coordination).
For wireless security on the deployed WLANs, see Wi-Fi Security and WPA/WPA2/WPA3. For enterprise 802.1X authentication on wireless, see 802.1X Port Authentication and RADIUS Configuration.
Accurate timestamps on RF events require NTP to be configured on the WLC. Forward coverage hole and DFS alerts to a central syslog server for persistent storage.

Next Steps: For multi-AP FlexConnect branch deployments where RF planning directly impacts standalone-mode roaming, see FlexConnect AP Configuration. For the guest WLAN where RF coverage affects WebAuth captive portal reachability, see Guest WLAN with WebAuth. For 802.11 protocol standards including 802.11ac/ax channel bonding specifications, see 802.11 Standards and Frequency & Channels. For autonomous AP channel configuration without a WLC, see Autonomous AP Configuration. For network event logging of DFS radar events and RRM coverage hole alerts, see show logging and Syslog Configuration. For wireless security on the deployed WLANs, see Wi-Fi Security and WPA/WPA2/WPA3.

TEST WHAT YOU LEARNED

1. Why are only channels 1, 6, and 11 considered non-overlapping in the 2.4 GHz band, and why is Adjacent Channel Interference (ACI) considered worse than Co-Channel Interference (CCI)?

A. Channels 1, 6, and 11 are the only channels supported by 802.11g — all other channels are 802.11b only. ACI is worse because adjacent channels transmit at higher power, drowning out the primary channel B. Channels 1, 6, and 11 are reserved by the FCC for enterprise use. ACI is worse because adjacent channel transmissions are completely invisible to the 802.11 physical layer, bypassing CSMA/CA entirely C. 2.4 GHz channels are each 22 MHz wide but spaced only 5 MHz apart — channels 1 and 6 are separated by 25 MHz (5 × 5 MHz), which is just enough for zero spectral overlap. Any two channels with fewer than 5 channels separation overlap. ACI is worse than CCI because an adjacent-channel signal is partially but not cleanly decodable — the receiver cannot distinguish it from noise, causing uncorrectable frame errors and retransmissions. CCI is more orderly: co-channel devices participate in CSMA/CA and take turns, dividing throughput but not causing corruption D. Channels 1, 6, and 11 are non-overlapping because they use different modulation techniques (BPSK, QPSK, QAM). ACI is worse because adjacent channels share the same collision domain, causing twice as many collisions as co-channel interference

Correct answer is C. The 2.4 GHz band's channel layout is the source of the 1/6/11 rule. Each channel is 22 MHz wide but channels are defined at 5 MHz intervals starting from 2.412 GHz. Channel 1 is centred at 2.412 GHz and spans 2.401–2.423 GHz. Channel 6 is centred at 2.437 GHz and spans 2.426–2.448 GHz. The guard band between the end of channel 1 (2.423 GHz) and the start of channel 6 (2.426 GHz) is 3 MHz — just enough to avoid spectral overlap. Channels closer than 5 apart (e.g., channels 1 and 4) have overlapping spectra. The CCI vs ACI distinction is critical for understanding why the "use only 1/6/11" rule is absolute, not advisory. Co-channel devices follow CSMA/CA — they hear each other, defer, and take turns. This reduces throughput (all share the same time) but does not cause corrupted frames. Adjacent-channel interference creates a signal that partially bleeds into the receiver's passband — the receiver cannot cleanly reject it, leading to bit errors, FCS failures, and retransmissions. See Frequency & Channels for the full channel frequency map.

2. A Cisco WLC has DCA configured in Automatic mode with the full 2.4 GHz channel list (channels 1–11) enabled. What problem will this likely cause, and what is the fix?

A. RRM's DCA algorithm optimises mathematically for minimum interference, and may determine that channel 4 or channel 8 causes less interference than channels 1, 6, or 11 in specific scenarios. This results in adjacent APs being assigned partially overlapping channels — creating adjacent channel interference that is worse than the co-channel interference it was trying to avoid. The fix is to remove all channels except 1, 6, and 11 from the DCA allowed channel list, forcing RRM to choose only from non-overlapping options B. DCA with all channels enabled causes the WLC to exhaust its processing capacity — running DCA calculations for 11 channels is computationally expensive and causes the WLC to crash. Restrict the list to reduce WLC CPU load C. Having all 11 channels enabled causes DCA to run more frequently — the increased channel change rate disrupts clients. The fix is to set DCA sensitivity to Low to reduce the channel change frequency D. No problem — DCA is intelligent enough to always choose 1, 6, and 11 from the full channel list regardless of what options are enabled

Correct answer is A. DCA's mathematical optimisation does not have an inherent preference for channels 1, 6, and 11 — it simply finds the assignment that minimises measured interference across all APs in the RF Group. In a real deployment, it is entirely possible for DCA to determine that channel 4 has lower measured interference than channel 1 at a specific AP because of the particular RF geometry. But channel 4 overlaps with both channels 1 and 6 — any AP on channel 4 creates adjacent channel interference with APs on those channels. The human operator knows that only 1, 6, and 11 are valid 2.4 GHz choices; DCA does not know this unless you restrict the channel list. The fix is: Wireless → 802.11b/g/n → RRM → DCA — uncheck every channel except 1, 6, and 11. Then force a DCA recalculation with config 802.11b channel global once. This is the single most important RRM misconfiguration to know for the exam. See Frequency & Channels.

3. What does the RRM Transmit Power Control (TPC) algorithm target with its default -70 dBm threshold, and what are the consequences of setting the maximum TX power too high?

A. TPC targets a minimum client RSSI of -70 dBm — it increases AP power until all connected clients are heard at -70 dBm or stronger. High maximum power causes APs to overdrive their power amplifiers, reducing hardware lifespan B. TPC targets the noise floor — it adjusts power until the SNR at each AP is at least 70 dB. High power causes the noise floor to rise from the transmitter's own phase noise, reducing SNR paradoxically C. TPC targets a maximum inter-AP interference of -70 dBm — it reduces power until neighbouring APs hear each other at -70 dBm or weaker. High maximum power causes channel utilisation to rise above 70%, triggering more frequent DCA recalculations D. TPC targets each AP being heard by at least 3 neighbours at -70 dBm — ensuring coverage overlap is sufficient for seamless roaming. If the threshold is met with lower power, RRM reduces TX power; if fewer than 3 neighbours are heard at -70 dBm (potential coverage hole), RRM increases power. Setting maximum TX power too high creates large, heavily overlapping cells — clients at the edge of AP-A's range still hear AP-A more strongly than the closer AP-B and refuse to roam (sticky client), causing poor throughput from the high-latency, low-rate connection to the far AP

Correct answer is D. TPC's design philosophy is neighbour-centric: an AP needs enough power so that its immediate neighbours can confirm it exists and coverage is contiguous, but not so much that its cell expands beyond the coverage boundary of co-channel neighbours. The -70 dBm threshold ensures seamless roaming — a client moving between two adjacent APs will always find at least one AP at usable signal strength. The sticky-client problem is the most visible symptom of over-powered cells: a client's 802.11 association logic uses RSSI to determine whether to roam, and if a far AP is heard at -75 dBm (because it is transmitting at full power), the client will maintain that association even when another AP just 5 metres away is also heard at -75 dBm — it perceives no reason to roam. Cap maximum power to match client device capabilities (~17 dBm) and ensure TPC is in Automatic mode. Verify after changes using ping tests to confirm client connectivity.

4. `show advanced 802.11a summary` shows NetsTuts-AP-05 is transmitting on channel 36 with TX Power Level 1 (maximum). All other APs on the same floor are also on channel 36. RRM DCA is set to Automatic. What is the most likely cause?

A. The RRM interval has not elapsed since the APs were deployed — wait for the next DCA run (up to 10 minutes) and channels will be automatically distributed B. The DCA allowed channel list for 5 GHz has been restricted to channel 36 only — DCA cannot distribute channels beyond what is in the allowed list. Expand the DCA channel list to include UNII-1 (36, 40, 44, 48) and UNII-3 (149, 153, 157, 161, 165) and force a recalculation with config 802.11a channel global once C. The APs are not registered to the RF Group — they are making independent channel decisions and all defaulting to channel 36 as the first channel alphabetically D. 5 GHz channel 36 is the only channel that supports 802.11n — the other APs are 802.11n-only and cannot use channels above 48

Correct answer is B. DCA can only assign channels from its allowed list. When the allowed list contains only one channel, DCA has no alternative — every AP on the floor receives that single channel. This most commonly occurs when someone carefully removed all channels from the DCA list except one during a misconfiguration or testing exercise, or when a default configuration only includes channel 36 and no one expanded it. The fix: navigate to Wireless → 802.11a/n/ac → RRM → DCA and add the desired 5 GHz non-DFS channels to the allowed list. Then run config 802.11a channel global once to trigger an immediate DCA recalculation rather than waiting for the next scheduled interval. In a floor with multiple APs, having all on the same channel causes severe co-channel interference and dramatically reduces wireless performance — this is a configuration problem, not a hardware one. Log the event and monitor with show logging after fixing.

5. What is an RF Group and why is it important to configure when deploying multiple WLCs in the same physical building?

A. An RF Group is a VLAN used to separate wireless management traffic from data traffic — it prevents WLC-to-AP control messages from interfering with client data flows B. An RF Group is a security group that defines which wireless clients are permitted to associate with which APs — similar to a whitelist. Different RF Groups can apply different Wi-Fi security policies to different areas of the building C. An RF Group is a set of WLCs that coordinate RRM decisions for APs in a shared physical space. One WLC is elected RF Group Leader and runs DCA and TPC for all APs across all member WLCs. If two WLCs in the same building are not in the same RF Group, each WLC's APs make independent channel and power decisions — APs managed by WLC-A might be assigned the same channel as adjacent APs managed by WLC-B, creating co-channel interference that neither WLC is aware of or will correct D. An RF Group defines the physical location boundaries of the wireless network — WLCs in different RF Groups cannot share FlexConnect groups or SSID configurations

Correct answer is C. Without RF Group coordination, each WLC operates its RRM independently, treating the other WLC's APs as unknown external interference sources. Consider: WLC-A manages APs on floor 2 west, WLC-B manages APs on floor 2 east. Without RF Group coordination, WLC-A's DCA might assign channel 36 to its easternmost AP (AP-West-5) because none of its managed APs conflict. WLC-B's DCA independently assigns channel 36 to its westernmost AP (AP-East-1) for the same reason. These two APs are adjacent and on the same channel — severe co-channel interference — but neither WLC knows the other's assignment. In an RF Group, the Leader WLC has visibility into all AP assignments across both WLCs and would never assign the same channel to adjacent APs regardless of which WLC manages them. The RF Group name must be configured identically on all WLCs: config rf-network name [name]. For multi-site deployments, also see FlexConnect AP Configuration.

6. `show advanced 802.11a coverage` shows AP NetsTuts-AP-07 generating 35 coverage hole alerts over 24 hours, and `show ap auto-rf 802.11a NetsTuts-AP-07` shows the AP is already at TX Power Level 1 (maximum). What does this indicate and what is the correct action?

A. The TPC threshold is set too aggressively — lower the threshold from -70 dBm to -85 dBm so fewer clients trigger the coverage hole detection algorithm B. The AP's radio is faulty — replace the AP hardware. A working AP at maximum power should never trigger coverage hole alerts C. The AP is too close to other APs — reduce its TX power to prevent interference with neighbours, which is causing the false coverage hole alerts from RSSI measurement errors D. This is a physical AP placement problem that cannot be resolved through configuration. RRM has already exhausted its power-based response (maximum TX power) and the coverage hole persists. The correct action is a physical site survey — walk the affected area with a Wi-Fi analyser to locate the signal gap, then either reposition the AP closer to the gap, add a new AP to cover the area, or investigate RF-absorbing obstacles (concrete walls, metal shelving, elevator shafts) that may require a different antenna or AP type

Correct answer is D. Coverage hole alerts when the AP is already at maximum TX power are the definitive indicator that the problem is physical, not configurational. RRM's TPC algorithm responds to coverage holes by increasing TX power — it has done exactly this and reached the hardware ceiling. At this point, RRM can do nothing more. Lowering the coverage hole threshold (option A) would suppress the alerts but not fix the underlying coverage gap — clients would still experience poor signal, just without WLC visibility. The cause is almost always one of: (1) the AP is too far from the coverage area — it was placed for convenience rather than RF coverage (e.g., in a closet or above a false ceiling in a corridor when it needs to cover a large room), (2) a physical obstruction between the AP and the area — thick concrete walls, metal mesh flooring, or server racks absorbing RF energy, or (3) the floor plan has changed since the AP was installed. The only resolution is physical: move the AP, add an AP, use a directional antenna, or remove/penetrate the obstruction. Verify the fix with ping tests and monitor show logging for continued coverage hole alerts.

7. Why do 5 GHz DFS channels (UNII-2A: 52–64, UNII-2C: 100–144) require special handling, and what behaviour should an engineer expect when deploying APs on these channels?

A. DFS (Dynamic Frequency Selection) is a regulatory requirement to protect radar systems (weather radar, military radar, air traffic control) that operate in the same frequency range. Before using a DFS channel, the AP must perform a Channel Availability Check (CAC) — listening for 30–60 seconds to confirm no radar is present. If radar is detected during operation, the AP must vacate the channel within 10 seconds and cannot return for at least 30 minutes. This can cause sudden client disconnections and service interruptions in environments near airports, weather stations, or military facilities B. DFS channels require a special Cisco DFS license — without it, the WLC will not enable these channels even if they are added to the DCA channel list. Contact Cisco to obtain the DFS licence for the specific country C. DFS channels are higher power channels — they require the AP to transmit at minimum 23 dBm, which interferes with the TPC algorithm and must be excluded from automatic power control D. DFS channels operate at a different frequency modulation than non-DFS channels — 802.11 clients must support DFS-mode hardware to connect to APs on these channels. Legacy 802.11a clients cannot use DFS channels

Correct answer is A. DFS is an IEEE and regulatory mandate (FCC in the US, ETSI in Europe, and other regional bodies) requiring 5 GHz devices to detect and avoid radar systems. Radar signals take priority over Wi-Fi — radars do not implement CSMA/CA and will not yield to Wi-Fi transmissions. The CAC requirement means when an AP first tries to use a DFS channel (on boot, after a DCA channel change, or after returning from a radar evacuation), it must listen for 60 seconds (indoor) before transmitting a single frame. During this listening period, no clients can associate. This is why APs on DFS channels appear "unavailable" for up to 60 seconds after a reboot or channel change — they are performing the mandatory CAC. When radar is detected during operation (common near airports, military bases, and some industrial equipment), the AP evacuates the channel immediately and clients are disconnected. Log DFS events with show logging and forward them to a central syslog server for persistent monitoring. See 802.11 Standards for regulatory context.

8. A wireless network has eight 5 GHz APs deployed across a single floor. `show advanced 802.11a summary` shows that four of the APs are on channel 36 and four are on channel 40. DCA is in Automatic mode. What is the most likely cause and fix?

A. The WLC has a channel reuse algorithm bug — apply the latest WLC firmware to resolve the DCA calculation error B. The DCA 5 GHz channel list has been restricted to only channels 36 and 40 — perhaps a previous administrator disabled all DFS channels and also removed most non-DFS channels. With only two channels available, DCA cannot achieve better distribution regardless of the RF geometry. Add all UNII-1 channels (36, 40, 44, 48) and UNII-3 channels (149, 153, 157, 161, 165) to the DCA allowed list and force a DCA recalculation with config 802.11a channel global once C. RRM cannot assign more than two unique channels to any single floor — the per-floor channel limit must be increased in the WLC advanced settings D. The RF Group Leader is offline — without a leader, DCA defaults to the first two channels in the list. Re-elect the RF Group Leader to restore full DCA operation

Correct answer is B. DCA can only assign channels from its configured allowed list. If the allowed list contains only channels 36 and 40, then DCA has no choice but to divide the APs between those two channels — the algorithm cannot create additional diversity from a list of two. This scenario often occurs after an administrator disabled DFS channels (a valid decision) but also unintentionally removed non-DFS channels like 44, 48, 149, 153, 157, 161, and 165 from the list. The fix is straightforward: navigate to Wireless → 802.11a/n/ac → RRM → DCA and ensure all desired non-DFS channels are checked. For eight APs with the UNII-1 + UNII-3 non-DFS channel set (8 channels: 36, 40, 44, 48, 149, 153, 157, 161), DCA has exactly enough unique channels to assign a different channel to each AP — ideal for eliminating co-channel interference on the floor. After expanding the channel list, run config 802.11a channel global once to trigger an immediate DCA recalculation without waiting for the next scheduled interval. Monitor the result with show logging.

9. What is the difference between DCA Sensitivity set to "High" versus "Low", and which setting is appropriate for a hospital wireless deployment?

A. High sensitivity enables DCA to use the full channel list including DFS channels; Low sensitivity restricts DCA to non-DFS channels only. Hospitals should use Low sensitivity to avoid DFS-related service interruptions B. High sensitivity increases the TPC transmit power threshold; Low sensitivity decreases it. Hospitals with large open wards need High sensitivity for maximum coverage distance C. DCA sensitivity controls the minimum RF improvement required to trigger a channel reassignment. High sensitivity requires only a 5 dB improvement to change channels — more frequent reassignments. Low sensitivity requires a 30 dB improvement — channel changes only in severe interference scenarios. A hospital should use Low sensitivity because wireless medical devices (patient monitors, infusion pumps, clinical handsets) running active sessions cannot tolerate the brief connectivity interruption caused by a channel change. Stability takes absolute priority over RF optimisation in clinical environments D. High sensitivity and Low sensitivity produce identical channel assignment results — the sensitivity setting only controls the DCA reporting verbosity in WLC logs

Correct answer is C. DCA sensitivity is a stability vs responsiveness trade-off. The threshold is how much better (in dB) a new channel assignment must be compared to the current one before DCA will make the change. High (5 dB threshold): DCA changes channels aggressively in response to relatively small improvements. Good for environments where the RF landscape changes quickly and optimal channel assignment is more important than stability — retail floors, venues, outdoor deployments. Medium (15 dB threshold, default): suitable for most enterprise environments — responds to significant interference without constant disruption. Low (30 dB threshold): DCA only makes a channel change when the current channel is severely compromised. Channel changes are rare — the network is highly stable but may not be RF-optimal. Critical infrastructure environments — hospitals, manufacturing control systems, SCADA networks, warehouses with RF-dependent logistics systems — prioritise stability. A channel change, even a brief one, can disrupt a medical device's wireless session and cause a clinical alarm, potentially requiring nurse response or device reconnection. Low sensitivity ensures the network stays on its assigned channels unless the interference is catastrophic. For enterprise authentication on the deployed WLANs, see RADIUS Configuration.

10. An engineer checks `show ap auto-rf 802.11b NetsTuts-AP-Kitchen` and finds channel utilisation at 85% and interference at 35% on a 2.4 GHz radio near the building's kitchen. The AP is on channel 6 with only 12 clients. What is the most likely cause and appropriate remediation?

A. Too many co-channel APs nearby — DCA has failed to assign unique channels. Force DCA to reassign: config 802.11b channel global once B. 12 clients are overloading the AP — this is a capacity problem. Add a second AP near the kitchen and enable band steering to distribute clients C. The AP's TPC power level is too high — reduce to power level 5 to shrink the cell and reduce the channel utilisation measurement area D. The 35% non-802.11 interference is the primary indicator — microwave ovens operate at 2.45 GHz (directly overlapping channel 6 in the 2.4 GHz band) and transmit when in use, generating broadband RF energy that does not implement CSMA/CA and blocks the channel. The high channel utilisation (85%) is a consequence of the microwave interference — the AP's CCA (Clear Channel Assessment) detects the RF energy and defers, but the deferred time still counts as channel utilisation. Remediation: use show 802.11b cleanair air-quality summary to confirm microwave interference as the source. Then disable 2.4 GHz on the kitchen AP and rely on 5 GHz coverage for that area (microwaves do not operate at 5 GHz), or enable Band Steering to move dual-band clients off 2.4 GHz automatically

Correct answer is D. The combination of high channel utilisation (85%) + high non-802.11 interference (35%) + low client count (12) is the classic signature of a non-802.11 interferer, not a capacity or channel assignment problem. With only 12 clients, an 802.11-only channel utilisation of 85% would be extraordinary — 12 clients rarely saturate a 2.4 GHz channel to that degree. But the 35% non-802.11 interference tells a different story: a non-802.11 device is consuming 35% of the channel's airtime with energy that the AP cannot CSMA/CA-defer around. Microwave ovens are the most common culprit in kitchen environments — they generate broadband 2.4 GHz interference at 2.45 GHz (channel 8–9 centre) that bleeds strongly into channel 6 and causes exactly this pattern. CleanAir (if enabled on the AP) will classify and name the interferer type. The practical resolution is to operate the kitchen area on 5 GHz only — modern smartphones and laptops are all dual-band capable and 5 GHz is completely immune to microwave oven interference. Log the event with show logging for documentation. See Frequency & Channels for the full 2.4 GHz frequency map.

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