WLC Active/Active vs Active/Standby

[Alexmpj376]

What are all advantages of using Redundancy mode for WLC's vs using Active/Active mode

[Prakash Parvathala]

1:1 where one WLC will be

in an Active state and the second WLC will be in a Hot Standby state continuously monitoring the health

of the Active WLC via a Redundant Port. Both the

WLCs will share the same set of configurations

including the IP address of the Management interface. The WLC in the Standby state does not need to

be configured independently as the entire configuration (Bulk Configuration while boot up and

Incremental Configuration in runtime) will be synced from the Active WLC to the Standby WLC via a

Redundant Port. The AP's CAPWAP State (only APs whic

h are in a run state) is also synced, and a mirror

copy of the AP database is maintained on the Standby WLC. The APs do not go into the Discovery state

when the Active WLC fails and the Standby WLC takes over the network's Active WLC.

There is no preempt functionality. When the previous

Active WLC comes back, it will not take the role

of the Active WLC, but will negotiate its state with the current Active WLC and transition to a Standby

state. The Active and Standby decision is not an

automated election process. The Active/Standby WLC

is decided based on HA SKU (Manufacturing Ordere

d UDI) from release 7.3 onwards. A WLC with HA

SKU UDI will always be the Standby WLC for the first time when it boots and pairs up with a WLC

running a permanent count license. For existing

WLCs having a permanent count license, the

Active/Standby decision can be made based on manual configuration

For more information about the redundancy you can look into the HA availability guide below.

http://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/7-5/High_Availability_DG.pdf

[roger perkin]

Alex, 

There are no real advantages between Redundancy mode vs Active / Active it all depends on your topology and failover scenarios and downtime you can sustain. 

Lets step through all the possible options. 

1: Single controller 

All your AP's will register to the single controller and if this controller fails you will have no wireless service until that controller has been restored. 

2: 2 x Controllers in Active / Standby 

With this setup you will have two controllers running in an Active / Standby configuration. They will share the same IP and configuration. They can be located in the same location or at two geographically separate locations (if you can provide L2 connectivity between both controllers) 

All AP's register to a single IP address and if the primary controller fails the APs will not experience any downtime as they will instantly move to the standby controller. 

3: Redundant Controllers

In this setup you have a primary controller in one location and a second controller in another location. APs will register to the primary controller and also be configured to have the second controller as a backup. In the event of a failure of the primary controller the AP's will have to re-associate to the secondary controller which could be up to 120 seconds and will result in downtime for clients.

As for advantages of either setup you need to assess your budget and downtime requirements. 

Then based on your requirements you choose the best solution. 

Hope that helps

[Alexmpj376]

Great, thanks for the answer

[Mohammad Setan]

Simply in HA, if your primary controller went down, the AP's will go directly to the secondary without any interruption (APSSO), and your clients will not disconnect (Client SSO if it is supported). both controllers will share the same configuration including the management IP address.

In active-active clients will disconnect and the AP will disconnect if the one controller went down, because the AP will go with the joining process with the second active controller.

Kind Regards

Mohammad Setan