DHCP option 43 for Cisco WLC

Setting up Switch to work as a DHCP server for AP with option # 43

Scenario – WLC is connected in a network on Mgmt.(inline) interface – say - Vlan 100 and APs are connected at the access layer on Vlan 200. You want the APs to boot up and get an IP address from the DHCP and along with that you can set the option # 43 to assign the Wireless Lan controller (WLC) management ip address. By doing this, as soon as the DHCP will send the IP address to the AP, it will also send WLC information, the AP needs to join. The dhcp scope in this scenario is defined on the switch where you have the WLC and APs terminating, on different interfaces and different Vlans.

Configuration steps on switch.

1.       Create vlan 100 for WLC management on switch1 and assign a port into that Vlan and connect your switch

Vlan 100

name WLC_MGMT

Vlan 200

name AP_MGMT

interface vlan 100

WLC_MGMT_VLAN

ip address 10.10.10.1 255.255.255.0

no shut

interface vlan 200

description AP_MGMT_VLAN

ip address 192.168.50.1 255.255.255.0

no sh

interface g1/0/1

description  ##### -Connected to WLC-#####

switchport

switchport mode trunk

switchport trunk all vlan 100,200

no sh

interface g1/0/10

description  #####- Connected to AP1-#####

switchport

switchport mode access

switchport access vlan 100

no sh

interface g1/0/11

description  #####- Connected to AP2-#####

switchport

switchport mode access

switchport access vlan 100

no sh

               

2.       Configuration step on WLC

a.       On WLC, go to controller – interface ( on left side) and click on management interface

b.      Assign the IP address 10.10.10.5, netmask – 255.255.255.0 and gateway – 10.10.10.1

Setting up DHCP Pool configuration on switch1

ip dhcp pool APvlan200

network 192.168.50.0 255.255.255.0

default-router 192.168.50.1

option 43 hex f104.0a0a.0a05 ---------< check below to understand the conversion

Converting decimal to Hex and using it in the above command (DECIMAL to HEX)

NOTE – f104 will be default and rest of the value will come after conversion. Check the conversion example below

IP to be converted – 10.10.10.5

Open the calculator in the programmer mode and click Dec and type 10 after typing 10 click on Dec (option below that) the value will be “A”. So use it as 0A

Now 10 becomes – 0A

And now convert 5 into hex like before; it will come as ‘5’ so use it as 05.

The hex conversion of the above ip is – 0A.0A.0A.05.

Now break it slots of 4 and make sure to prepend it with f104 in case of one controller and prepend it with f108 for two controllers. The final hex value will look like this

f1040a0a0a05

In case we need to configure two controllers with IP address 10.10.10.5 and 10.10.10.6. The hex value for option 43 will become f1080a0a0a050a0a0a06. The prepend value in case of two WLC will become f104 * 2 = f108.

By following the above steps your APs should start getting the IP addresses and WLC information. 

To check the reachability, try to ping the AP from your WLC and you should be able to ping it and do it vice-versa. Once the AP is booted properly, it should join the controller. If still not, then make sure you are not running with the issues like MIC check, mac-filtering or mac list authentication etc. under the AP policies in security tab.