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24 Feb 15 DHCP options for Cisco 2600 Series Access Points

Configuring DHCP Options for Cisco 2600 Series Access Points

I do not have to do this much so when I do I have to always look it up hence I decided to write it in my own words for my reference. Normally when I put Cisco Access Points on the same VLAN as the Wireless LAN Controllers Management Interface. Access Points have no issue joining the controller. However if the Cisco light weight access Points are on a different VLAN, they will not be able to join the controller initially and that usually requires DHCP Options 43 and 60. Below is an overview of how to configure DHCP Options 43 and 60 for Cisco light weight access points on a Cisco IOS Router.

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 and 60

ip dhcp pool AP_POOL
network 192.168.10.0 255.255.255.0
default-router 192.168.10.1
option 60 ascii “Cisco AP c2600” (I found this from Cisco website and is considered as the VCI String – Vendor Class Identifier)
option 43 hex f104c0a8010b

Note: Option 60 is not required when using Cisco IOS DHCP Server. But having that option will basically not send option 43 to clients that do not require it

Now getting the option 60 part is easy. 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

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