WLC 4400 and multi-subnet APs - Clients can associate but can't find DHCP

[Jonathan Chellis]

Hi all,

Hosting a WLC 4400 on one building/subnet (10.103.0.0, all traffic on VLAN 103). I'm trying to install APs in another building/subnet (10.106.0.0, all traffic on VLAN 106). Buildings are connected through a core L2 switch. APs I install in 10.106.x.x are pre-configured to find the 10.103.x.x controller and can find and associate with it without issue.

Each building/subnet has it's own DHCP server, gateway, and DNS.

I want my wireless clients in 10.106.x.x to use the on-site DHCP server but setting the DHCP override on that WLAN to the DHCP server in 10.106.x.x results in no traffic. Clients can associate with the WLAN but cannot find DHCP. Removing the override gets them the DHCP hosted on 10.103.x.x. 

Any help is appreciated. Please let me know if I need to supply more specifics.

Thanks.

[Rasika Nayanajith]

Hi

You need to have dynamic interfaces on the subnets where you want wireless uses get IP from.

In this case it require two dynamic interfaces, one in 10.103.x.x range & other 10.106.x.x range. Once you configure that, then you need to allow those vlan traffic to WLC (ie link between SW & WLC to be configured as a trunk link & allow those vlan).

When a wireless client send a DHCP request , WLC will use correspoding vlan dynamic interface IP address as source of the DHCP request when forwarding to your DHCP server. In this way DHCP server know which IP to assign for that request.

HTH

Rasika

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[Carlos Leiton]

Hi Jonathan,

I can see two possible solutions for this deployment:

1- As Rasika said on the below post, the data traffic from the APs is being sent through the capwap tunnel to the WLC. Therefore if you want to use multiple VLANs, you need to create a dynamic interface for VLAN 106 on the WLC, and also configure the switch port that goes to the WLC as trunk, allowing both VLANs 103 and 106. Then you map the WLAN you want to the corresponding WLC interface of VLAN 106.

2- The other possibility that I can see, is to avoid the data traffic to travel until the WLC location, and configure the APs on H-REAP mode.
Also, inside the WLAN you can configure H-REAP Local Switching. This was the traffic will stay local , the Access Points will forward the data traffic to the switch they are connected, you have the option to map the WLAN to an specific VLAN, or by default the clients will get an IP address from the same subnet than your APs have.

If you want to go for any of these options, I can send you further indications if you want.

Hope this helps.