Controller Based WLANs

What is the concept of Airgroup? How does it work and what are the basic troubleshooting commands that are available?
Question What is the concept of Airgroup? How does it work and what are the basic troubleshooting commands that are available?
Environment This article applies to Aruba Mobility Controllers running ArubaOS version 6.3.0.0 with Airgroup enabled.

 

Zeroconf is a set of protocols that enable service discovery, address assignment and name resolution for desktop computers, mobile devices and network services. It is designed for flat, single-subnet IP networks such as wireless networking at home.
 
Bonjour, Apple’s trade name for its zeroconf implementation, is the most common example. It is supported by most of the Apple product line including the Mac OS X operating system, iPhone, iPod Touch, iPad, Apple TV and AirPort Express.
 
Bonjour uses multicast DNS (mDNS) to locate devices and the services that those devices offer. Since the addresses used by the protocol are link-local multicast addresses, each query or advertisement can only be forwarded on its respective VLAN, but not across different VLANs. Network administrators are faced with a difficult choice between propagating mDNS traffic across VLANs – and risking a significant reduction in wireless performance – or blocking mDNS traffic to prevent connectivity for Bonjour-capable devices and services.
 
Aruba AirGroup adds mDNS proxy capabilities to campus WLANs so that Bonjour messages can be forwarded across subnets or VLANs. 


How it works:



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. 

Once controller receives an mDNS query, controller replies with a unicast response containing relevant mDNS records from its cache table. By default, all AirGroup servers are visible to all AirGroup users.



Basic troubleshooting commands:


Airgroup is enabled by default on controller after upgrading to ArubaOS 6.3.0.0. Below command shows the status of  airgroup on the controller:

#show airgroup status



Airgroup feature can be enabled/disabled using the following command in the config mode:

(Aruba)(config)#airgroup [enable|disable]



Airgroup service can be enabled/disabled using the following command in the config mode:

(Aruba)(config)#airgroup service <service-name> [enable|disable]


Airgroup is by default disabled for IPv6 clients. It can enabled/disabled with below command in the config mode:

To enable:


(Aruba)(config)#airgroup ipv6  

To Disable:

(Aruba)(config)#no airgroup ipv6


Airplay and Airprint services are enabled by default. Status of the airgroup services can be seen using the "show airgroup status" command.

 

 

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Aigroup, by default is allowed on all vlans. Below command shows if the airgroup is allowed or disallowed on a particular vlan:

 

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AirGroup classifies all mDNS devices as either AirGroup servers or AirGroup users. Devices which advertise at least one Bonjour service are classified as AirGroup Servers whereas devices which do not advertise but query for Bonjour services are classified as AirGroup Users.

List of Airgroup servers that a controller can listen across vlans can be seen using the below command:

#Show airgroup servers

 

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List of Airgroup users that a controller has seen the queries coming from:


#Show airgroup users


List of cache entries on a airgroup controller can be seen from the below command:

#Show airgroup cache entries

 

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Excessive mDNS packets from devices can impact the performance of AirGroup. Throttling mechanism such as "credit values" has been added to rate limit the number of mDNS packets processed by the controller. Controller assigns separate credit values to query and response packets. Credit is decremented by one, when a query or response packet is processed by controller. Controller will drop any query/response packets when the corresponding credit is zero. Credit values are renewed every 15 seconds.

To see the current credit value on a controller user the command "show airgroup global-credits"

 

 

 

On the Airgroup controller, there would be some of  the mDNS queries receiving from the users, for which there are no servers offering the service. This list of queries will be displayed under blocked queries.

Below is the command to look at blocked queries:


#Show airgroup blocked-queries

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Based on network requirement, some of the aigroup services might be disabled on controller but it  might be still receiving queries from users. This count of number of queries is shown using the command "show airgroup blocked-service-id"

 

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Version history
Revision #:
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Last update:
‎07-11-2014 04:40 PM
 
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