Aruba UAP discovery

How a factory default Aruba Universal AP discovers just what it’s supposed to be in the world is a source of some confusion, not least because the process changed (I believe around AOS 8.4). For a thorough explanation of how things used to work see here.

Put simply all current UAPs (shipped with AOS8.6 or 8.7 at the time or writing) take a cloud first approach, which flips on its head what Aruba APs always used to do.

It’s perhaps worth explaining what a Universal AP actually is. Aruba UAPs can operate in Instant or Campus mode. A campus AP (CAP) talks to a Mobility Controller. An Instant AP (IAP) can be standalone or operate as part of an IAP cluster with one AP taking the role of Virtual Controller. It used to be each model of AP had separate CAP and IAP versions. An IAP could be converted to CAP mode but a CAP could only be a CAP. There was some weird geopolitical reason for this that eventually went away hence the more sensible Universal AP became the norm.

So what happens?

A factory default UAP follows this logic:
– Attempts to contact Aruba Activate
– Connect to Airwave if DHCP option/DNS entry exists
– join a virtual controller on the local subnet
– Listen for a virtual controller (layer 2)
– Look for a mobility controller (layer 2 ADP/DHCP options/DNS)
– Broadcast setmeup SSID
– Reboot after 15 minutes

Of course if the AP receives config at any of these steps, it does what it’s told and doesn’t proceed through the discovery logic.

What’s changed in this list from older software version (pre 8.4) is the cloud wins. If your UAP can connect Activate, and there’s a rule there telling it what to do, that’s what it does. If that rule is incorrect you could see some unexpected behaviour.

The other significant change is looking for a mobility controller is now pretty much bottom of the list. You might be used to an AP looking for a mobility controller as the first thing it does, which indeed is what used to happen, but not longer. So if you run a controller environment and manage to end up with a VC running on an AP subnet you’ll find other new APs form a IAP cluster with this and nothing appears on the mobility controller. Once this happens it’s possible to convert all the APs to campus mode, pointing them at a mobility controller, so this isn’t too painful.

This cloud first approach makes a lot of sense and when it all works smoothly Activate rules can make ZTP provisioning of a new UAP very smooth.

In many deployments it isn’t unusual to have no internet access for APs, especially campus APs. In this scenario, to avoid odd behaviour, make sure your AP subnet is configured with the correct DHCP options or DNS entry for the mobility controller.

If you find a new UAP doesn’t appear to be working, e.g. it hasn’t appeared on your mobility controllers, there’s every possibility that something else along the discovery logic has taken precedence.

Finally it’s worth noting you can manually set controller options from the AP-boot prompt by connecting to the AP console and interrupting the boot sequence. Any static configuration is acted on first. This approach doesn’t scale of course, but it’s useful for testing and building a small lab environment alongside an active system.

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