topic Re: Replacement CISCO Catalyst 9800-L-F wireless controller in Wireless

Replacement CISCO Catalyst 9800-L-F wireless controller

zhd27 — Fri, 10 Oct 2025 03:58:10 GMT

I have a client who is currently using a Catalyst 9800-L wireless controller (exact model and version not confirmed yet) with 50 Access Points. They want to replace the current setup by using a new wireless controller, Catalyst 9800-L-F, along with 50 new APs (AP model not confirmed yet).

For one week, both wireless controllers (old and new) and all APs (old and new) will be running in parallel. After that, the old controller and old APs will be removed.

In the current setup, the old controller is connected to the Cisco core switch, and from the core switch, a Cisco PoE switch is connected, where all old APs are physically connected.

I want to know:

What are the pre-checks (OS version, cable, etc.) I should do?

How should I deploy the new controller and APs?

Can you provide a deployment guide for my learning?

Note: I'm not sure which DHCP method they are using — it could be via an SVI, the controller itself, or another external DHCP server. However, I do know they are using a RADIUS server for authentication. AND This is my first wireless deployment project.

ZHD

Re: Replacement CISCO Catalyst 9800-L-F wireless controller

Mark Elsen — Fri, 10 Oct 2025 06:44:29 GMT

- @zhd27 >...For one week, both wireless controllers (old and new) and all APs (old and new) will be running in parallel.
That's not advisable, it will confuse access points.

>...What are the pre-checks (OS version, cable, etc.) I should do?
Check compatibility of new access point models and intended software version on the new controller
using : https://www.cisco.com/c/en/us/td/docs/wireless/compatibility/matrix/compatibility-matrix.html
https://www.cisco.com/c/en/us/support/docs/wireless/catalyst-9800-series-wireless-controllers/214749-tac-recommended-ios-xe-builds-for-wirele.html

>...How should I deploy the new controller and APs?
You could copy the running configuration from the old controller and import it in the new one
(minor changes will probably be needed, for configuring interfaces)

>...Can you provide a deployment guide for my learning?
Not exactly but this is a good guide for starters
https://www.ciscolive.com/c/dam/r/ciscolive/global-event/docs/2024/pdf/BRKEWN-2094.pdf

>... I'm not sure which DHCP method they are using
You need to find out before the replacement

Last but not lease : validate the configuration of the new controller using the CLI command
show tech wireless and feed the output from that into Wireless Config Analyzer

Re: Replacement CISCO Catalyst 9800-L-F wireless controller

Saikat Nandy — Fri, 10 Oct 2025 15:42:46 GMT

Just to add what @Mark Elsen said -

>...For one week, both wireless controllers (old and new) and all APs (old and new) will be running in parallel.
That's not advisable, it will confuse access points.
Update: If your APs are WLCs are running on same vlan, then it will be a problem in case APs drops off from WLC. Via broadcast, it will seen both the WLCs and might join the new one. However if your APs and WLCs are in different vlans then this issue arise from broadcast can be avoided. Better do manual priming to all the APs so that it joins to the same WLCs even after drop off (assuming it will get response back from it's Primary WLC).

>...Can you provide a deployment guide for my learning?
Not exactly but this is a good guide for starters
https://www.ciscolive.com/c/dam/r/ciscolive/global-event/docs/2024/pdf/BRKEWN-2094.pdf
Update: You can follow this guide too - https://www.cisco.com/c/dam/en/us/td/docs/wireless/controller/9800/17-4/deployment-guide/c9800-webui-dg.pdf

>...Note: I'm not sure which DHCP method they are using — it could be via an SVI, the controller itself, or another external DHCP server.
Update: The recommendation is to use external DHCP server. You should use only L2 VLAN in the 9800 WLC. The uplink switch should have the SVI of the VLANs along with the ip helper details. You can go through this best practise guide to understand DHCP and a lot of other best practises - https://www.cisco.com/c/en/us/td/docs/wireless/controller/9800/technical-reference/c9800-best-practices.html