topic Some wireless devices getting same IP address in Wireless

Some wireless devices getting same IP address

mcaoile — Mon, 05 Jul 2021 15:16:03 GMT

Hi,

I have configured an interface group were it consists of 4 subnets /24. DHCP server is microsoft windows. IP addresses are leased in round robin between the 4 subnets. What I noticed is that some smartphones are having duplicate IP address and always assigned the same IP address and in the same subnet. Example.

iPhone : MAC (30:07:4d:86:99:37) IP: (192.168.133.11)

Samsung: MAC (a0:18:28:8f:63:b5) IP: (192.168.133.11)

Even though I tried to disconnect and reconnect, the Samsung phone still gets the same IP. Tried to 'forget' the WLAN and reconfigure, still, it gets the same IP.

Why is it not getting a different IP on any of the interfaces that has been grouped?

WLC is 5520 HA, code is 8.2.166.0

Regards,

Manuelito

Regards,

Re: Some wireless devices getting same IP address

Ric Beeching — Mon, 19 Feb 2018 08:55:42 GMT

Hi Manuelito,

I believe the WLC uses a hashing algorithm to assign clients that previously were on X interface back to that same one as this permits for a smoother overall experience.

The WLC will round robin new clients but by placing known/existing clients back on the same interface they won't change IP Address constantly as they roam/refresh their lease etc/reconnect etc.

Hope that helps,

Ric

Re: Some wireless devices getting same IP address

mcaoile — Mon, 19 Feb 2018 09:20:20 GMT

Hi Ric,

Thks for the reply.

My problem now is some devices having ip conflict

Manuelito

Re: Some wireless devices getting same IP address

Flavio Miranda — Mon, 19 Feb 2018 09:23:44 GMT

I don't believe WLC is responsible for that since you are using external dhcp server.

WLC will send request iqualy through the interfaces inside a interface group.

Either if working as a proxy or transparent the WLC do not play any hole on the IP assignment. This must be entirely DHCP server responsibility.

The Microsoft documentation state that:

"A superscope allows a DHCP server to provide leases from more than one scope to clients on a single physical network"

As each interface Vlan can be seeing as one different network, this can be a problem to the dhcp server.

Make sure you have your server properly configured.

-If I helped you somehow, please, rate it as useful.-

Re: Some wireless devices getting same IP address

Ric Beeching — Mon, 19 Feb 2018 09:44:49 GMT

What's your lease timeout on your DHCP Server? You may want to extend that to prevent duplicate IPs although the devices should request a new one upon conflict anyway..

Ric