DHCP Option 43 between two WLCs

[Lorenzo46]

Hi,
I start to explain my topology:

I have 2 WLC 5508 (WLC-A and WLC-B) and 2 AP Type (AP-1242 and AP-1852).
Both APs are connected to a Cisco L3 Switch on which I have configured a DHCP Server with option 43 to give the ip address to both APs.
The WLCs are connected to another Cisco L3 Switch on a different network to APs.

WLC1
|_________                              _________ AP-1242
                   SW --------- SW
                    L3                   L3
_________                               _________ AP-1852
|
WLC2

My question is if it's possible to configure the DHCP with option 43 to have this result:
AP-1242 registered to WLC-1
AP-1852 registered to WLC-2

Thank you!

Best Regards
Lorenzo

[Flavio Miranda]

Hello,

  You can do that using Option 43  + Option 60. However, not on same DHCP scope. You can create a second DHCP scope:

ip dhcp pool <pool 01>
network <IP Network> <Netmask>
default-router <Default router>
dns-server <DNS Server>

option 60 ascii “c1200”
option 43 hex <WLC1 IP Address>

ip dhcp pool <pool 02>
network <IP Network> <Netmask>
default-router <Default router>
dns-server <DNS Server>

option 60 ascii “c1850”
option 43 hex <WLC2 IP Address>

[Leo Laohoo · Accepted solution]

I know what you're trying to do. You want the 1240 to register to WLC 1 because it's running an old software that supports only the 1240 and not the 1850.

WLC-2 for the 1852 because the firmware will only support 1852 but not 1240.

The answer to the question is WHY?

Let's say that you've got a simple DHCP Option 43 option that has WLC-1 as first priority and WLC-2 as second priority. Guess what happens?

The 1240 will join WLC-1 immediately without an issue. 1852 will attempt to join WLC-1 but is unable to, however, the same DHCP scope gives the 1852 another option to join another controller so the 1852 will join WLC-2 (after a few minutes of delay).

[Lorenzo46]

It's happened exatly what you have told. 

The AP1242 joins WLC-1 immediately without an issue. The1852 attempts to join WLC-1 but is unable to. The same DHCP scope gives the 1852 another option to join another controller so the 1852 joins to WLC-2.

Thanks for the support!

[Leo Laohoo]

Happy to hear it finally works. :)

[Peter Boerjesson]

This can be done and even within the same DHCP scope. I haven't done it on windows DHCP servers but in linux DHCP servers you can add "if" statements. So lets say

"if vendor identifier = Cisco AP 1242" provide option 43 WLC-A

"if vendor identifier = Cisco AP 1852" provide option 43 WLC-B

There's more to it than the few lines I wrote and it's not the "correct" syntax, I wouldn't be surprised if it was different between different release/flavours of Linux. My point is only if the device matches the if statement it will follow through and get an IP address and the corresponding options within that if statement.

[Flavio Miranda]

They are using Cisco Switch as DHCP server

"Both APs are connected to a Cisco L3 Switch on which I have configured a DHCP Server with option 43 to give the ip address to both APs.