Lightweight AP client getting wrong IP address from DHCP server

[stanley_cwy]

I have 2 units Cisco WLC 5508 running software version 7.0.220 with 70 over units Cisco AP 1262N and 1242AG. Some of wireless clients having problem to get the correct IP address from the DHCP server. There are 2 units of Microsoft DHCP. Both DHCP server ip have been configured on the Interface at the WLC. The core switch also being configured with ip helper. Not sure where goes wrong. Hope someone can give some light on this. I've attached the debug output of one of the wireless client during the problem.

[Surendra BG]

Correct ip meaning they r getting ip fron an unknown subnet??

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[stanley_cwy]

Correct IP mean the IP address meant for the VLAN.

For example I have below configuration:

SSID 1 with VLAN 33 (Network: 10.10.33.0/24)

SSID 2 with VLAN 60 (Network: 10.10.60.0/24)

Sometime client connected to the SSID able to get the IP from the subnet. Some client getting IP from other subnet which is used for other LAN users.

[mike.sprinkle]

How is the core switch SVI for vlan 33 configured? Does the ipaddress received by the client (10.10.7.179) fall within the subnet assinged to the SVI?

[stanley_cwy]

The core switch SVI for VLAN 33 is configured with ip helper pointing to both DHCP servers. In fact from the debug shows it is able to locate the DHCP server, just that instead of assigned with IP address 10.10.33.x, it has been assigned with 10.10.7.179 which belongs to other VLAN.

When this happen, the wireless client connection shows connected but unable to access to any network resouces including ping to gateway because the IP doesn't belong to VLAN 33. After few seconds, the wireless client will be disconnected.

[grabonlee]

Could you confirm if the APs are in local or HREAP mode? If local, what subnet IP does the AP obtain and if HREAP, what is the local VLAN mapping for clients? The clients will always obtain an IP address on the same VLAN as the AP, unless a separate VLAN is specified under HREAP and ofcourse the client VLAN must have IP helper address specified on the switch SVI and the subnet configured on the DHCP server.

[stanley_cwy]

APs are in local mode. APs and WLC are in same VLAN but client in 2 different VLANs with 2 different SSIDs with proper ip helper configured on SVI.

FYI, the clients might not necessary obtain IP address on the same VLAN as the AP in local mode.

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[Stephen Rodriguez]

Are you using AP groups? If so make sure the AP are in the correct group

Steve

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[stanley_cwy]

Not using AP group. All AP under default group.

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[grabonlee]

If you have clients on a different vlan, that means you have created dynamic interfaces on the 5508. With that in mind and looking at your attached file, it seems that you have configured Guest WLAN and Internal WLAN on the same WLC. The issue you have is on the Guest WLAN and I assume this based on the fact that the logs shows WEBAUTH_REQD and the client was attached to interface APSH-GUEST (10.10.33.x/24).

If the following assumptions are correct, the first step of troubleshooting would be to remove the external DHCP server from the picture and create a DHCP pool on the switch. If the clients pick up an IP on the correct VLAN, then that means your config setup is OK on the WLC. We can then ignore the WLC and look at the Switch/DHCP server and focus more on ACLs and DHCP scope.

[Amjad Abdullah]

Stanly,

I had no chance to see the debugs you sent but we need to verify some points:

- study all clients that show this behavior and make sure it is not a client issue.

- make sure you are not using interface groups under SSID config rather than using an interface.

- collect sniffer trace on DHCP server port to check the DHCP request and offer messages for further check.

Amjad

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[stanley_cwy]

Hi Osita Njokubi, I've tried configure DHCP on core switch and it's working fine. But I also tried the Microsoft DHCP server with wired/LAN users and it's working fine as well. It seems like integrating the wireless with Microsoft DHCP is having problem. Not sure where it goes wrong.

Yes, I have both internal and guest SSIDs. I'm having problem with both SSIDs actually. The debug only shows the guest SSID.

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[AndrewBarrington61628]

A very old thread - but did you ever get a resolution to this issue ?

Thank You.

[stanley_cwy]

Hi Amjad Abdullah, all clients have no issue because the issue happens randomly. Today this client is working but tomorrow might have problem. I'm not using any AP group. I have not do any sniffing on the DHCP server yet. Maybe will try that later.

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