I have two WLC 4402 servicing several SSIDs. Every SSID represents a different VLAN with a different IP subnet.
Now I want to use one DHCP server for all SSIDs. So I configured the server (I disinguish the requests from the different networks by option 82), put him into the VLAN where the ap-manager and the management interfaces are residing in and configured the DHCP server address of the interfaces on the WLC appropriate to the new setup.
Now my problem: No request arrives at the server. I now tried nearly all options but without success.
I found out that relaying works if the DHCP server is on the SAME subnet. Then all requests are relayed (yes, relayed, unicasted by the controller).
DHCP debug of the WLC says:
DHCP received op BOOTREQUEST (1) (len 313, port 1, encap 0xec03)
DHCP selecting relay 1 - control block settings: dhcpServer: 10.22.72.3, dhcpNetmask: 255.255.248.0, dhcpGateway: 10.22.72.33, dhcpRelay: 10.22.72.1 VLAN: 22
DHCP selected relay 1 - 10.22.72.3 (local address 10.22.72.1, gateway 10.22.72.3, VLAN 22, port 1)
DHCP transmitting DHCP REQUEST (3)
If now I enter the DHCP server address of the new server (directly reachable though the ap-amanager and management interfaces) I get the following:
DHCP received op BOOTREQUEST (1) (len 308, port 1, encap 0xec03)
DHCP selecting relay 1 - control block settings: dhcpServer: 0.0.0.0, dhcpNetmask: 0.0.0.0, dhcpGateway: 0.0.0.0, dhcpRelay: 10.6.72.1 VLAN: 640
DHCP selected relay 1 - NONE
It just seems to ignore the entered DHCP server address.
I tried several software versions (v4.2, v5.2), all the same.
DHCP proxy is enabled - as mentioned, if the DHCP server is in the same subnet, it works fine.
OK, so the DHCP server does not have a gateway, so it can't respond to a request on another network....That is the problem. With this config you would never get DHCP to work, as you had seen.
No the WLC will not send the DHCP request for x vlan out y vlan.....DHCP needs to be reachable..