DHCP Option 43 issues since migrating to Windows DHCP Server

[Andrew Souders]

Recently we moved to Windows DHCP from another vendor. My AP's are not finding the controllers based off of option 43. The DHCP Option 43 string for the a600 series is:

00 f1 08 0a 05 08 15 0a 05 08 16

Based off the Cisco document: http://www.cisco.com/c/en/us/support/docs/wireless-mobility/wireless-lan-wlan/97066-dhcp-option-43-00.html

Primary Controller is 10.5.8.21 = 0a050815

Secondary Controller is 10.5.8.22 = 0a050816

TLV Value = f108

The additional two 00 are in the document.

From running a wireshark packet capture the DHCP server is offering up the following string for Option 43

66 0b 00 f1 08 0a 05 08 15 0a 05 08 16 

Where does the 66 0b come from? When consoled into the AP the message in the logs is:
%CAPWAP-3-DHCP_RENEW: Could not discover WLC. Either IP address is not assigned or assigned IP is wrong. Renewing DHCP IP.

The AP model is AIR-CAP2602I-A-K9 and does get a valid IP in the correct subnet. The controllers are on a separate subnet.

The AP does try to find the controller by resolving CISCO-CAPWAP-CONTROLLER.kennedyhealth.org. The problem with that is based on subnet our AP's need to join specific controllers so Option 43 is preferred.

Before moving to Windows DHCP Option 43 worked correctly so I am fairly certain it is an issue with the sever, unfortunately, I have to request specific changes for the option 43 string.

[Sandeep Choudhary]

best is to delete it and config the new one.

https://networkguy.de/?p=899

https://blogs.technet.microsoft.com/troubleshooting_walk_through/2013/11/01/what-comes-with-option-43-and-configuring-in-dhcp/

Regards

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[Prateek Saxena · Accepted solution]

So if you closely look at the string 66 0b 00 f1 08 0a 05 08 15 0a 05 08 16 

66->Sub option code for 1000 model AP's

0b->total string length 11 (00 f1 08 0a 05 08 15 0a 05 08 16)

It looks like you have configured your DHCP server wrong and it is sending option code 66 rather than 2b which translates to option 43. 66 translates to 102 in binary.

The AP is not able to understand this option code, thus not taking the option 43

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[Andrew Souders]

This would be why on the server under option name it states "102 AP IP Provision" because it is using the 1000 model sub option?

[Prateek Saxena]

Exactly.. So if you go to the configuration link that you have attached, you need to follow the steps to configure the option 43 under "Other Cisco Lightweight Access Points" of Microsoft DHCP server configuration.. :)