upgrading IOS of access point on a slow wan link using local TFTP

[atifali.zaidi1]

my customer has 1800 access points joined to a 3850 express mobility switch ( switch acting as wireless controller ) , now i will need to migrate to central 9800 controller cluster , but because of slow wan link, the ap can join the 9800 controller but takes hours to complete the IOS download.  i was wondering if i can somehow upgrade the ap ios using a local TFTP server and then point to central 9800 so that it can just get registered without having to download the IOS ?

ap's are running the below IOS on express mobility controller 

AP Running Image : 16.3.7.0
Primary Boot Image : 16.3.7.0
Backup Boot Image : 8.3.143.0

my central 9800 controller is running 17.3.6

[Flavio Miranda]

Hi @atifali.zaidi1 

 I believe that would be the best strategy. Another one would upgrade your embedded WCL to the same version or closer. The embedded WLC is local to the site? 

[atifali.zaidi1]

so what i think i should do is apply 17.3.6 on the 3850 express mobility controller and then pre-download the ios to all the ap's .  and since we will need to move the ap's one by one , i can first swap the image on the ap which needs to be moved and then using capwap ap primary-base <hostname> <IP address> i can move them, they will simply join the 9800 controller and will get registered ?

[Flavio Miranda]

Sounds like a good plan.  You will have less working than manually upgrading the APs.

[atifali.zaidi1]

hi there, i was wondering if i can simply download the controller IOS version on the 3850-48P switch ? but the IOS version of the controllers is supposed to be chosen as per the model of the controller.   currently the embedded controller in this switch is running 17.3.7 and if i go the switch IOS downloads it can only support upto 16.x .  so a little bit lost here.

[Leo Laohoo]

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@atifali.zaidi1 wrote:
i was wondering if i can somehow upgrade the ap ios using a local TFTP server and then point to central 9800 so that it can just get registered without having to download the IOS ?

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Yes, this is what I would do (if I was in the same predicament).

[Rich R]

1. As you discovered you cannot upgrade the 3850 to current IOS-XE.  That product is end of life (Cisco abandoned it and pivoted to the 9800 series).

2. You'll have to get a TFTP server setup and then get CLI access to each AP enabled to install the image on AP using CLI.

3. If you have a server at the site then you could temporarily setup a 9800-CL on the server with the same version and join the APs to the 9800-CL first to do the download, and then let them join your central WLC when they've all finished downloading.

You're obviously still going to face the same issue when it comes time to upgrade, which you should be doing regularly to stay on supported software versions, but then you'll be able to use Efficient Image Upgrade or Out of Band Image Download:
https://www.cisco.com/c/en/us/td/docs/wireless/controller/9800/17-12/config-guide/b_wl_17_12_cg/m_eff_image_upgrade_ewlc.html to improve things.