topic Re: DHCP Issue with Local SSID on Virtual WLC 9800 (flex mode) in Wireless

DHCP Issue with Local SSID on Virtual WLC 9800 (flex mode)

sh-o — Thu, 09 Oct 2025 21:18:11 GMT

I am working on a virtual Cisco WLC 9800 setup.
The management interface is configured on GigabitEthernet1 with an IP address used for both management and data traffic.

I have configured three SSIDs, and the site operates in Flex mode.
Two of these SSIDs need to obtain DHCP addresses from an external DHCP server while operating in local switching mode.

However, I am facing an issue:

When I disable central switching and central DHCP, clients connect successfully.

When I enable central switching (to keep it in local mode) and expect DHCP to come from the external server, clients cannot obtain an IP address and fail to connect.

Could you please advise on the correct configuration or requirements to make external DHCP work with local switching SSIDs in Flex mode?

Re: DHCP Issue with Local SSID on Virtual WLC 9800 (flex mode)

Mark Elsen — Fri, 10 Oct 2025 07:30:21 GMT

- @sh-o >...When I enable central switching (to keep it in local mode) and expect DHCP to come from the external server, clients cannot obtain an IP address and fail to connect.
In that case debug a client using instructions from :
https://logadvisor.cisco.com/logadvisor/wireless/9800/9800ClientConnectivity
These results , so called RadioActive Traces can be analyzed with :
Wireless Debug Analyzer

>...Could you please advise on the correct configuration or requirements to make external DHCP work with local switching SSIDs in Flex mode?
I advise against doing that because it contradicts with the flexconnect application model.
Keep everything local : DHCP + local switching. Then clients can remain operational
when the central controller becomes unavailable ,

Re: DHCP Issue with Local SSID on Virtual WLC 9800 (flex mode)

Saikat Nandy — Fri, 10 Oct 2025 15:16:59 GMT

Just from your explanation it looks to be working as designed.
9800-CL was designed to be a flex-friendly setup although people have implemented for local mode/central switching setup as well.
Please follow this - https://www.cisco.com/c/en/us/support/docs/wireless/catalyst-9800-series-wireless-controllers/213945-understand-flexconnect-on-9800-wireless.html to understand how flex design should work as well as configuration.