Cisco Catalyst 9800 Series Wireless Controller Software Configuration Guide, Cisco IOS XE 26.1.x

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Cisco Catalyst 9800 Series Wireless Controller Software Configuration Guide, Cisco IOS XE 26.1.x

AP image download time enhancement

Updated: April 10, 2026

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Describes AP Image Download Time Enhancement for OEAP or Teleworker deployments.

AP image download time enhancement is a feature that

  • adds support to multiple sliding windows for control packets going from controller to AP

  • reduces image download time in Cloud and FlexConnect deployments where the AP and controller are separated by a WAN or Internet link, and

  • is supported only on OEAP profiles.

CAPWAP communication and window enhancement

The wireless controller and the access point (AP) communicate with each other using CAPWAP. The CAPWAP has two channels, namely control and data. The control channel is used to send configuration messages, download images and client keys, or the context to the AP. The control channel has a single window in the current implementation. A single window means that every message that is sent from the controller has to be acknowledged by the AP. The next control packet is not transmitted till the earlier one is acknowledged by the AP.

The AP Image Download Time Enhancement feature adds support to multiple sliding windows for control packets going from controller to AP. The sliding window can be set to N (static) instead of a single window. The request queue size is decided based on the maximum window size the AP supports.

The following table shows the recommended window size for different network conditions:

Table 1. Recommended window size

Link Bandwidth1

Less than 200 ms RTT

Greater than 200 ms RTT

More than 20 Mbps

10

15

Between 5 and 20 Mbps

10

15

Between 1 and 5 Mbps

5

10

Less than 1 Mbps

3

5
1 The window size recommendation provided in the table is for packet loss of less than one percent (< 1%). If the network supporting the CAPWAP link has packet loss of more than one percent (> 1%), use a smaller value for window size. For good links with round-trip time (RTT) of about 100ms and packet drops of less than half a percent (< 0.5%), use a window size of up to 20 for better performance.
Note

  • The window size can be changed only during the AP join process.

  • All image upgrades should be in the install mode for faster upgrade. Image upgrade should be done from the one-shot command to include OEAP predownload.

  • Configure the window size only for AP profiles that are exclusively used for Teleworker or Office Extend Access Points (OEAP).

  • An AP reload is not required after disabling this feature.

  • This feature is supported only on the OEAP profiles.

  • GUI does not support AP predownload. Therefore, the AP downloads after disjoining the controller during CAPWAP join phase. This causes a long disruption in the network as the Image download for AP can take upto one hour.

If you downgrade the software to Cisco IOS XE Gibraltar 16.12.4 or earlier from Cisco IOS XE Amsterdam 17.3.1, you should reset the CAPWAP multi window to a single window prior to the downgrade. Failure to do so necessitates a manual AP recovery.

High-level workflow for AP Image Download Time Enhancement:

  1. Select an existing AP join profile or create a new one.

  2. Set the CAPWAP window size.

  3. Associate the AP join profile to an existing site tag or new one.

  4. Apply the site tag to the AP using: Static, Filter, Location, AP, or Default mapping method.

Configure AP Image Download Time Enhancement (GUI)

AP Image Download Time Enhancement optimizes the download performance of access point images by configuring CAPWAP window size settings to improve data transfer efficiency.

Use this procedure when you need to optimize access point image download performance through CAPWAP configuration settings. This enhancement is particularly useful in environments with high-latency network connections or when managing large numbers of access points.

Follow these steps to configure AP Image Download Time Enhancement using the GUI:

Procedure

1.

Choose Configuration > Tags & Profiles > AP Join > CAPWAP > Advanced.
2.

In the CAPWAP Window Size field, enter the unit of measurement of the window.
3.

Click Save & Apply to Device.

The AP Image Download Time Enhancement configuration is applied to the device. Access points will use the optimized CAPWAP window size settings for improved image download performance.

Configure AP Image Download Time Enhancement (CLI)

Enable AP Image Download Time Enhancement to optimize the download process for access points.
AP Image Download Time Enhancement improves the efficiency of firmware downloads to access points by configuring the CAPWAP control packet transmit queue size. This configuration is particularly beneficial for teleworker or OEAP deployments.

Procedure

1.

Enter global configuration mode.

Example:

Device# configure terminal
2.

Configure an AP profile.

Example:

Device(config)# ap profile ap-profile-name

Example:

Device(config)# ap profile capwap_multiwindow
3.

Configure the AP CAPWAP control packet transmit queue size.

Example:

Device(config-ap-profile)# capwap window size window-size

Example:

Device(config-ap-profile)# capwap window size 20
Note

Configure the window size only for AP profiles that are exclusively used for teleworker or OEAP.

Be aware that any change in window size may impact other APs.
4.

Return to privileged EXEC mode.

Example:

Device(config-ap-profile)# end
The AP Image Download Time Enhancement is now configured with the specified CAPWAP window size, optimizing firmware download performance for the designated AP profile.

Verify AP image download time enhancement configuration

Verify AP Image Download Time Enhancement Configuration using commands to view CAPWAP window size, status, and modes.

To view the CAPWAP window size present in an AP profile, use this command:

Device# show ap profile name default-ap-profile detailed | in wind

Capwap window size : 10

To view the CAPWAP status and modes, use this command:

Device# show capwap client rcb 

OperationState                     : UP
Name                               : AP4001.7A39.2D5A
MwarHwVer                          : 0.0.0.0
Location                           : default location
ApMode                             : Remote Bridge
ApSubMode                          : Not Configured
CAPWAP Path MTU                    : 1485
Software Initiated Reload Reason   : Reload command
CAPWAP Sliding Window
Active Window Size                 : 10
Last Request Send To Application   : 184
Expected Seq Num                   : 185
Received Seq Num                   : 184
Request Packet Count               : 42424
Out Of Range Packets Count         : 0
Window Moved  Packets Count        : 0
In Range Packets Count             : 960
Expected Packets Count             : 41464

To view the AP configuration details, including the CAPWAP window size, use this command:

Device# show ap config general | in Wind

Capwap Active Window Size                       : 5
Capwap Active Window Size                       : 10
Capwap Active Window Size                       : 1