Problems with DHCP options

Hello everyone

I’m trying to roll out a network consisting of a Balance 30 Pro and switches/APs from a different vendor.
Because i won’t be the person performing the installation, i’m trying to pre-configure everything as much as possible but i’ve hit a roadblock.

The issue is that the devices use DHCP option 138 in order to receive the IP address of the cloud controller they have to connect to but option 138 is locked to the CAPWAP protocol in the Peplink firmware.
Is there a way to unlock option 138 so i can implement a custom value like in other unnamed options?

Any help is greatly appreciated!

Do you have the AP controller enabled on the Peplink, I beleive that locks the use of option 138 as it’s used by Peplink APs for discovery purposes. On a 20X running 8.1.3 where the AP controller is not enabled I was able to configure a DHCP server with option 138 just fine, admittedly I did not test that it actually sends the configured response - if it does not send the configured response then a support ticket should certainly be opened as that is in my eyes a bug.

Are there no other discovery options supported by your APs? Most APs I have ever touched from Cisco, Ruckus, Aruba etc. all support some flavour of DNS based discovery to tell the APs where to find their controller.


Just read your post again, you can ignore the “CAPWAP Access Controller addresses” text on the Peplink gui, just use the option and set it to give out the necessary IP. That text is just there for a reference it is not parsed in the responses. If your APs ask for option 138 in their DHCP request they should receive whatever is configured there.

Hello Will, thanks for the response!

The APs we use only support informing via dchp which is rather unfortunate.

In the meantime i’ve done some tests with wireshark to check the dchp offers given by the peplink and while i’ve come to the same conclusion as you that option 138 just gives the ip entered in the field which would be completely fine. However for some reason our Balance 30 Pro running firmware 8.13 sends out the same ip address twice within option 138. I can’t confirm it’s the ultimate cause yet but i suspect that the fact the APs are getting 2 IP addresses instead of the expected 1 might be causing them to to fail to find the controller.

When compared to option 138 on a router of a competing brand, the other router only sends the IP once and the APs have no problem.

I don’t assume that sending duplicate IPs is an intended feature on Peplink’s end and i’ve since submitted a support ticket.

Well packets don’t lie so if you’re seeing the IP sent twice that’s probably worth engaging Peplink support over as that sounds like a potential bug to me! :slight_smile: