How is master IAP elected in an IAP cluster?

Aruba Employee

Environment  :  Product and Software: This article applies to Aruba Instant Access Points (IAP's) running on Aruba InstantOS and later.



Aruba Instant does not require an external mobility controller to regulate and manage the Wi-Fi network. Instead, one IAP in every network assumes the role of a Virtual Controller (VC).

The Master Election Protocol enables the Aruba Instant network to dynamically elect an IAP to take on a VC role. This protocol ensures stability of the network during initial startup or when the VC goes down by allowing graceful failover to a new Virtual Controller when the existing VC is down.

Below-mentioned is the brief description on the Election Process:

  • IAP boots up, stay in ‘INITIAL’ state for a while, if it receives any master beacon, it becomes slave.
  • If no master beacon received, transition to ‘Pot-Master’ state (Pot: Point of Time) and stay for a while. If it receives any master beacon during this period, trigger the conflict resolve algorithm to compute a new master.
  • If no master beacon received, transition to ‘Master’ state and start to broadcast master beacon. If it receives any master beacon during this period, trigger the conflict resolve algorithm to compute a new master.
  • At any time, if a slave do not hear master beacon for a while, it uses the same manner to do the transition.

IAP uses following order as Conflict Resolve Algorithm, to resolve conflicts:

  1. look into IP scope. IAP with default-ip cannot win
  2. look into 3G capability
  3. look into AP class, Arran (IAP-13x) gets higher priority
  4. look into uptime, older AP gets higher priority
  5. look into AP MAC, bigger address gets higher priority

NOTE: If it is a single IAP in the network running with default-ip, then it would take  the role of VC.

Normally, adding a new IAP into a cluster will not affect the existing Master, but again there are 2 exceptions to this rule as mentioned-below:
  • Master is running with default-ip, a new IAP comes up and gets DHCP address and thereby becomes the new Master. At the same time, any IAP with default-ip will reboot automatically for IP recovery.
  • Master (without 3G dongle) is UP for less than 5 mins, then a new IAP (with 3G dongle) comes up. The new IAP becomes the new Master.

NOTE: IAP Master Election Process, do not take InstantOS in to consideration. After the Master is elected, the virtual controller can take of image synhcronization with slave IAP's.


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‎07-02-2014 01:05 PM
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Hello guys,


This beacon works in the wired site?

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