Configuring DHCP Options for Cisco Access Points

This is a quick reference on configuring DHCP Option 43 in Cisco IOS so that Cisco access points are able to find/join the controller residing in a different VLAN.

I will use 192.168.10.0/24 network as an example where all the Cisco light weight access points will reside. Controller IP would be lets say 192.168.1.11. So now since the Cisco Access Points and the Wireless LAN Controller are on two different subnets. I would need to configure DHCP Options 43

ip dhcp pool AP_POOL
network 192.168.10.0 255.255.255.0
default-router 192.168.10.1
option 43 hex f104c0a8010b

DHCP Option 43 calculation requires further explanation:

• Option 43 is basically Type(f1) + Length(Number of Controller Management IP’s x 4) + Value (IP Address in Hex)
• Type = Will always be f1
• Length = This value comes from taking the number of Controllers Management IP’s and multiplying it with 4. So if there is a single controller then 1 X 4, if there are two then 2 X 4. so in our cause it would be 1 X 4 = 04
• Value = This is basically the IP address of the Controllers management interface into Hex so 192.168.10.11 = c0.a8.01.0b