Controllerless Networks

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Occasional Contributor II

About preemption in a Master active-active High Available AP Fast Failover Scenario

Hello

we have 2 controllers configured as masters without VRRP.

1 HA Group with both controllers in Dual mode

2 AP System profiles with lms ip (controller 1) and Backup lms ip (controller 2) and the other profile with reverse lms IPs.

The preemption is only enabled in the HA Group, because Aruba say this so. Now is the problem, that if the connection from one AP to primary controller is interrupted, then the AP move to backup controller. But not back after the configured preemption time.

What can be the problem?

Aruba Employee

Re: About preemption in a Master active-active High Available AP Fast Failover Scenario

Hi Steffen,

 

Please provide the following information:

 

1. When both controllers are active, are you seeing the active tunnels on one controller & standby tunnels (S flag) on the backup controller.

 

If the failover is done using HA config, then only the preemption will take place.

 

By any chance is the AP's failed over due to legacy method, preemption will not occur as it is disabled in the AP system profile.

 

Eg:

 

Master : 10.1.1.1

Local   : 10 .1.1.2

 

HA profile:

 

10.1.1.1 role dual

10.1.1.2 role dual

preemption

 

 

AP system profile

 

LMS: 10.1.1.1

Backup LMS: 10.1.1.2

 

LMS :Preemption disabled

 

In the above example , this will be the sequence of events:

 

1. AP will up on the master.

 

Standby tunnel will be formed to local controller which can be checked with the following command:

 

show ap database (S flag should be there)

 

2. Master goes down

 

AP will activate its tunnel to local. (S flag will go away).

 

3. Master controller recovers.

 

Now the standby tunnel will be seen on Master (S flag) for the same AP.

 

4. Once the LMS holdown period (600 s default value)  has passed, AP will move back to master  controller & standby tunnel (S flag) will be seen on local controller again.

 

 

Note: If you are not seeing the S flag in your setup, that means HA is not working as expected. So, if master goes down, AP will failover to local using legacy failover mechanism of lms/backup lms.

 

As preemption is disabled in the AP system profile, AP will not move back to master in this case.

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