topic Maximum number of Wireless Controllers allowed under DHCP Option 43? in Wireless

Maximum number of Wireless Controllers allowed under DHCP Option 43?

brent.boghean — Sun, 04 Jul 2021 08:18:16 GMT

Hello Support Community,

I have a client that has a very large wireless environment and they are looking into redundancy schemes for a mult-homed/multi-dacenter setup. I am being asked to find out what the maximum number of WLC's IP addresses that they can specify under DHCP Option 43. The research I have done so far specifies a minimum value of 1 byte, but the maximum value is variable.

The length field is 2 HEX characters and every 4th HEX character is a valid entry:

The length = N * 4 (where N is the number of WLC IP addresses in the field)

Therefore if all length values are valid this means that one could have 42 (or 41 if AA is not a valid entry) but this seems excessive and I'm thinking this would break something somewhere.

There are plenty of examples online with 0x08 for the length, which equals 2 controllers.

Cheers to any advice folks can provide, Thanks!

Brent

Maximum number of Wireless Controllers allowed under DHCP Option

Leo Laohoo — Thu, 21 Nov 2013 00:18:15 GMT

Option 43 for wireless, in my personal opinion, has one (and only one) function: To direct NEW wireless access points (AP) to the desired "staging" WLC.

Once the APs "arrive" to the designated WLC, a responsible engineer then assigns the AP the primary, secondary and tertiary WLC to go to.

Re: Maximum number of Wireless Controllers allowed under DHCP Op

Sandeep Choudhary — Thu, 21 Nov 2013 07:38:19 GMT

Hi Brent,

I do agree with Leo....

Option 43 is a vendor specific, and is used by Cisco APs to find and join WLC controllers.

for more clarification please visit this.

https://supportforums.cisco.com/videos/1423

Hope it helps.

Reagrds

Sent from Cisco Technical Support iPhone App

Maximum number of Wireless Controllers allowed under DHCP Option

brent.boghean — Thu, 21 Nov 2013 16:54:22 GMT

I reached out to the rest of the consultants at the company I work for, Long View Systems, and sure enough I got a response back with the answer:

"As far as the max. # of WLC in Opt 43, it may be that the max theoretical is 42 or 41, but APs only store up to 24 learned controllers in NVRAM."

He mentioned to me the same thing about how Option 43 is typically used for staging as well, which I was already aware of. Next time on the forums I will try to be more specific with the question I am asking.

Cheers

Maximum number of Wireless Controllers allowed under DHCP Option

brent.boghean — Thu, 21 Nov 2013 16:57:05 GMT

Sorry the forum will not let me mark my own post as a correct answer.

Maximum number of Wireless Controllers allowed under DHCP Option

Augustgood — Thu, 21 Nov 2013 17:05:46 GMT

after wlc discovery the ap learn all conttroller ip from a mobility domain.

Maximum number of Wireless Controllers allowed under DHCP Option

Augustgood — Thu, 21 Nov 2013 17:10:08 GMT

One mobility group can support 24 controller.