Controller Based WLANs

Explain Airgroup functionality in a single and multi-controller model. What commands are used to debug?

by on ‎07-10-2014 12:57 PM
Question Explain Airgroup functionality in a single and multi-controller model. What commands are used to debug?
Environment This article applies to Aruba Mobility Controllers running ArubaOS version 6.3.0.0

 

Prior to ArubaOS 6.3, Airgroup could only be enabled on single controller. This is changed from ArubaOS 6.3.0.0. Airgroup now supports multiple mobility controllers in a domain. This feature enables an iPad users on one controller to discover Apple TV available on another controller, when both controllers are part of the same domain.


In Single Controller Model:
 
  • AirGroup controller act as an mDNS proxy. It terminates all mDNS packets and sends out unicast responses to user queries.
  • The mDNS process on controller will receive all mDNS packets destined to UDP port 5353 with destination IP address 224.0.0.251. 
  • When AirGroup service is enabled, controller sends out an mDNS query for all the services which have been enabled on the controller on all allowed VLANs. AirGroup servers respond to this query with the records of services they advertise.
     
  • Controller adds learned records to AirGroup cache table and adds the device to AirGroup Servers. 
     
  • When a wireless / wired user sends mdns query looking for servers, then controller looks into airgroup cache table and sends a unicast response.

Below image shows the airgroup server discovery process on a Single Controller:
 
rtaImage.jpg
 
In Multi-Controller Model:


In multi-controller deployment, controllers can be part of one or multiple domains. One domain out of the configured domains can be an active domain.

Each controller in the domain will independently maintain the cache for connected devices and
 will respond with any matching records for any mDNS queries received from its wireless/wired users. The controller will also add meta data to same mDNS query and forward it to other controllers in the domain using PAPI. Other controllers in the same domain will respond with matching records after applying appropriate policies.


Below image shows how the querying user will be able to discover servers on other controllers in a domain:
 
rtaImage2.jpg
 
Multi-controller domains are defined on the master controller with the IP addresses of all controllers to be part of the domain. Controller will participate in cluster when the corresponding domain is added to its active domain list. A controller can be part of multiple domains based on the active domain configuration.

Any controller that shares VLANs with another controller must be part of the same AirGroup multi-controller cluster.


In a multi-controller deployment, there is a scaling limit of 2000 AirGroup servers and 16000 AirGroup users for all controllers in a cluster. If you require more servers and users than the prescribed limit, configure multiple clusters so that each cluster is within the prescribed limit.

Whereas, in Single controller model, it depends on the individual controller:


Controller Model
No. Of Airgroup Servers
No. of Airgroup Users
3200XM 500 1500
3400 1000 3000
3600 2000 6000
M3 2000 6000
7210 2000 9000
7220 2000 12000
7240 2000 16000



Airgroup Domains and Airgroup Active Domains can be seen with the following command in the CLI prompt:

# Show airgroup domain
 
rtaImage3.jpg
 
 
# Show airgroup active-domains
 
rtaImage4.jpg
 
 
NOTE: The Status may show "Excluded" if the IP address of the controller is misconfigured.


All controllers communicate with each other based on the multi-controller table in an AirGroup cluster. This table is combination of controllers specified in each domain, as part of active-domains.

# Show airgroup multi-controller-table



For debugging AirGroup issues, enable debugging for mDNS process under system, security and user debug logs.
 
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