topic Re: Flex WLC client with same IP address in Wireless

Flex WLC client with same IP address

ANKUSH_SINGLA — Fri, 21 Mar 2025 13:30:08 GMT

Hi Team,

we have a setup for flex wlc with Guest WiFi services via C9800-CL Controller . we have meraki locally on each site which is acting as DHCP server.

Scenario - i have two sites using same DHCP scope , tomorrow there is possibility that clients from both sites takes same IP , will WLC allow to have two clients with same IP , as our ISE server Authenticate users with MAC address.

Re: Flex WLC client with same IP address

Mark Elsen — Fri, 21 Mar 2025 14:36:35 GMT

- I think in more recent versions , this is no longer a problem , but you should use 17.9.x or above (not older).
Also always validate the C9800-CL Controller's configuration with the CLI command :
show tech wireless and feed the output from that into Wireless Config Analyzer
Please note : do not use show tech-support for this procedure (use the full command as shown in green)
The use of this procedure should be considered mandatory!

P.s: I now moved this post to
https://community.cisco.com/t5/wireless/bd-p/discussions-wireless

Re: Flex WLC client with same IP address

Scott Fella — Fri, 21 Mar 2025 14:43:20 GMT

I will add my thoughts to this. I don't think this would be a good idea because it can cause more issue later on especially if your are routing that vlan. If you have local egress for guest in each site it might work, but then again, the single controller might be alerting on duplicate mac. The main issue is that the Meraki, I'm assuming your MX, does not know of the other MX handing out, so just make sure that is not routing internally. I don't see why you would not just use the same vlan id, but create a different dhcp scope. That would simplify everything and you would know what subnet belongs to what site, especially for troubleshooting.

Re: Flex WLC client with same IP address

Rich R — Fri, 21 Mar 2025 19:29:27 GMT

Yes it will work but like @Mark Elsen said you must use recent code (it wasn't possible in older 9800 code) - see TAC recommended link below.

You must also configure "ip overlap" on the flex profile otherwise the WLC will report "IP theft" and exclude the clients. Your sites must also have unique site tags.
wireless profile flex <flex-profile-name>
ip overlap

See https://www.cisco.com/c/en/us/td/docs/wireless/controller/9800/technical-reference/c9800-best-practices.html#FlexConnectsitetag