C9800 CleanAir and Spectrum Intelligence Explained

Why CleanAir and Spectrum Intelligence Matter

When you operate a wireless network—especially one covering challenging environments—you're working in unlicensed spectrum. Wi-Fi is fundamentally a free-for-all medium where every device must follow the same basic rules: listen before transmitting, back off when collisions occur, share the airtime fairly. The problem is that Wi-Fi devices are not the only transmitters using 2.4 GHz and 5 GHz bands. Non-Wi-Fi devices (Bluetooth speakers, microwave ovens, cordless phones, video cameras, baby monitors, medical devices) operate in the same spectrum without respecting Wi-Fi protocols at all. This creates a complex, unpredictable interference landscape that directly impacts your network performance and user experience.

This is where spectrum intelligence and CleanAir come in. These Cisco technologies give you visibility into what's actually happening on the wireless medium and help you detect, identify, and mitigate interference from non-Wi-Fi sources. Understanding how these work is critical when troubleshooting performance issues, planning deployments, or studying for advanced Cisco certifications (CCNP Wireless, CCIE Wireless).

Understanding Spectrum Intelligence

Spectrum Intelligence (SI) is the broad capability of detecting and recognizing other types of transmitters operating in your Wi-Fi bands. All Cisco Catalyst access points use their Wi-Fi radio chipset to capture as much data as possible from transmissions that occur on the bands they monitor. Because the AP cannot decode these non-Wi-Fi signals, it analyzes their patterns instead: bandwidth, hopping sequences, duty cycle, signal strength, and temporal characteristics.

From these patterns, the AP makes educated guesses about what type of device or protocol is transmitting. This activity of detecting and recognizing non-Wi-Fi transmitters is called spectrum intelligence. It represents a passive but valuable form of environmental awareness that doesn't require special hardware (in earlier generations) and doesn't consume performance resources directly during normal operation.

CleanAir: Dedicated Spectrum Analysis

Higher-end Cisco Catalyst access points embed a dedicated, software-programmable radio chipset alongside the standard Wi-Fi radio. On Wi-Fi 4 and Wi-Fi 5 access points (802.11n and 802.11ac), this is called a Cisco CleanAir chipset. The Catalyst 9120 and 9130 series access points include a separate software-defined radio of a new generation that performs the CleanAir duty. These dedicated radio chipsets include a full-blown spectrum analyzer that is specialized in this task.

The key difference is that CleanAir can perform continuous, high-resolution spectrum analysis while the AP is actively transmitting. When the Wi-Fi radio is transmitting, it drowns out everything else on the channel, so the Wi-Fi radio cannot monitor the medium simultaneously. The CleanAir chip has a very high sampling rate and dedicated hardware. This allows the CleanAir chip to detect different Bluetooth transmitters that hop at the same time to different neighboring 1 MHz-spaced frequencies (a capability standard Wi-Fi radios cannot match).

Both spectrum intelligence and CleanAir focus on detecting non-Wi-Fi interferers. CleanAir does so with better resolution and detect more types of interferers. The latter has a small performance impact because the AP needs to spend a bit more time off-channel to perform the detection, whereas CleanAir has no performance toll whatsoever (except only if you enable Bluetooth Low Energy (BLE) detection by CleanAir, which causes a 10 percent packet loss on the 2.4 GHz band).

Interferer Device Reports (IDRs)

CleanAir provides real-time interferer device reports (IDRs) back to the controller, which you can view under Monitoring > Wireless > CleanAir Statistics. Each report contains critical information for understanding interference impact:

The severity score is a summary metric that gives you quick visibility into relative impact. It is influenced primarily by duty cycle (the higher the percentage of time the interferer is transmitting, the greater the impact) but also by proximity and loudness (if an interferer transmits at very low signal strength and is far away, its severity is less).

Air Quality Index (AQI)

Another metric reported by CleanAir is the air quality (AQ) index. This is a rolling average calculation (indexed 0-100, where 100 represents perfection) of the number and severity of interferers present on a given channel. CleanAir takes a rolling average of the interferers to compute this metric. This metric helps give you an easy overview of the channel when interferers may come and go and not be constantly present in the real-time interferer list.

Configuring CleanAir

CleanAir configuration happens at Configuration > Radio Configurations > CleanAir. You can enable CleanAir globally and then check the CleanAir status (up or down) for each AP depending on its support for CleanAir. The same location allows you to enable spectrum intelligence for non-CleanAir-capable APs.

There is little reason to disable CleanAir because it does not bring a performance impact. It is, however, recommended to keep spectrum intelligence disabled if your network is sensitive to performance or a small packet loss due to the increased off-channel activity.

You can enable the reporting of interferers (otherwise, only air quality indexes are calculated) and select which interferer is reported. The BLE beacon is the only one excluded by default because it has some performance impact, whereas all other interferer types do not have any performance toll.

Configuration Page Overview

Monitoring the Spectrum Live

APs with the CleanAir capability allow you to connect to them and see the live view of their spectrum. This basically means having as many spectrum analyzers onsite as you have APs, and all of them are accessible remotely without any effort. In the past, having this capability required putting the AP in a special mode called SE-connect, but this mode is not required anymore. Simply go to Configure > Access Points and click a CleanAir-enabled AP. In the General section of the settings, you can find the CleanAir NSI key, which you need to connect to the AP, as illustrated below.

To connect to the AP spectrum analyzer, you need either Cisco Spectrum Expert or some third-party tool that supports CleanAir APs. You can then connect to the AP and enter the NSI key to see the live spectrum. Cisco DNA Center also allows you to view this within your web browser and without entering any key; to do so, click Spectrum Analysis in the AP 360 Assurance view, as shown below.

When you view the live spectrum through Cisco DNA Center, you see a real-time waterfall display of frequency occupancy over time. The horizontal axis shows frequency channels, and the vertical axis shows time progression. Areas of high intensity (bright colors) indicate active transmissions or interference; darker areas represent idle spectrum. This visualization helps you quickly spot interference patterns, hopping behavior, and other spectrum anomalies without needing a separate tool.

Interferer Location Tracking

If you have Cisco CMX or DNA Spaces, it is possible to locate interferers on the map. This capability, however, suffers from several issues that impact its accuracy. While Wi-Fi APs can report signal strength, determining direction requires either angle-of-arrival techniques (which require multiple antennas or antenna arrays and precise phase calibration) or time-difference-of-arrival calculations across multiple APs. The latter depends on precise time synchronization and is more accurate with a higher density of APs. In practice, interferer location is approximate and best used as a general indicator of where a problem might be, not as a precise fix location.

Supported Interferer Types

CleanAir can recognize and report on the following interferer categories:

Practical Troubleshooting with CleanAir Data

When you encounter users reporting poor performance in a specific area or on a specific band, CleanAir data provides objective evidence of interference. Use the workflow below:

1. Navigate to Monitoring > Wireless > CleanAir Statistics and filter by the affected band (2.4 GHz or 5 GHz)
2. Identify interferers by type, duty cycle, and severity score
3. Note which channels are affected according to the IDR
4. Cross-reference the affected channels with your WLAN configuration
5. If affected channels are in use, consider:
   • Shifting your primary WLAN to a less-affected channel
   • Reducing transmit power temporarily to limit coverage overlap with the interferer
   • Working with the facility to relocate or disable the interfering device (Bluetooth speaker, video camera, etc.)
6. Monitor the AQ index over time to verify improvement

CLI Commands for Spectrum and CleanAir Inspection

You can also gather CleanAir and spectrum data from the controller using CLI commands. These are useful for scripting, automation, or when you prefer command-line interfaces:

# Show CleanAir status and configuration
show ap cleanair summary

# Display all detected interferers
show ap cleanair interferer-list

# View air quality index for a specific band
show ap cleanair air-quality-index

# Get detailed statistics for a specific AP
show ap cleanair detail ap-name <ap-name>

# Display spectrum analysis data (if supported)
show ap spectrum analysis

# Verify CleanAir NSI key for remote connection
show ap name <ap-name> general | include "NSI"

Key Takeaways

• Spectrum Intelligence is a passive analysis capability present on all Cisco Catalyst access points; it detects non-Wi-Fi transmitters by analyzing their characteristics without decoding them.
• CleanAir is a hardware-accelerated, dedicated spectrum analysis engine on higher-end APs (Catalyst 9120/9130 series) that provides higher resolution, better interferer type detection, and no performance impact during normal AP operation.
• Interferer Device Reports (IDRs) provide specific data: closest AP, interferer type, affected channels, duty cycle, severity score, RSSI, device ID, and cluster ID for cross-AP correlation.
• The Air Quality (AQ) index (0-100) gives you a rolling average view of spectrum health on each channel, accounting for both the number and severity of interferers.
• CleanAir configuration is straightforward: enable it globally, choose which interferer types to report, and disable BLE detection only if you need to avoid the 10% 2.4 GHz packet loss toll.
• Real-time spectrum viewing via Cisco DNA Center or Spectrum Expert is available on CleanAir APs using the NSI key; no special SE-connect mode is required.
• When troubleshooting performance issues, use CleanAir data to identify the source of interference, determine affected channels, and make informed decisions about channel selection, AP placement, and facility-level mitigation.
• Interferer location tracking is possible with CMX or DNA Spaces but should be treated as a general indicator rather than a precise location due to accuracy limitations.