This guide is based on a real world deployment and covers all the aspects of the Cisco WLC 2504 High Availability Configuration.
I will be using the topology below.
The Cisco 2504 is a small form factor wireless controller suitable for small to medium sized organisations. It is the only model in the 2500 series.
With support for up to 75 access points and 1000 clients it is a very powerful box.
Cisco 2504 High Availability
In terms of high availability the 2504 does not support SSO (Stateful Switch Over). With the larger controllers you configure them as an HA pair with a single virtual IP address and in the event of a failure of a single controller the AP will seamlessly associate to the second controller.
The 2504 failover model is N+1. This means a Primary controller with a backup controller. There is no communication between the two controllers and they operate as standalone devices, so you have to configure them separately and license them separately.
The failover scenario
Within the AP you configure a Primary and a Secondary controller address.
Go to Wireless / Access Points / All APs / <Click on an AP> / High Availability
The AP is constantly checking that both controllers are active. In the event that the primary controller is unavailable the AP will associate to the secondary controller, this is not a seamless transition and clients will notice a drop but in less than 60 seconds service is resumed.
In order to support this failover on the secondary controller you need to do one of two things.
Ensure the secondary controller is licensed to support the same amount of access points as the primary. (This can be an expensive option)
The most common scenario is to purchase an HA-SKU controller AIR-CT2504-HA-K9.
For a standard controller the HA is replaced with the number of built in license i.e AIR-CT2504-5-K9 - this is a 5 AP license box and is the smallest number of licenses you can purchase.
This is a box dedicated only for failover situations. It does not contain any built in licenses but will support up the maximum for the box (75) access points in the event of a failover for a period of 90 days.
After which time you will start to get license alerts from the controller - after 90 days the access points will continue to work.
You can also convert a standard controller i.e a air-ct2504-5-K9 into an HA-SKU box with the following command
config redundancy unit secondary - as shown below
(Cisco Controller) >show redundancy summary Type of the Unit = Primary (Cisco Controller) >config redundancy ? unit Configure redundancy unit [primary | secondary] (Cisco Controller) >config redundancy unit ? primary Redundancy unit type is primary secondary Redundancy unit type is secondary (Cisco Controller) >config redundancy unit secondary (Cisco Controller) >reset system The system has unsaved changes. Would you like to save them now? (y/N) Y Configuration Saved! System will now restart! Updating license storage ... Done. ## Controller reboots and comes back as a secondary unit ## (Cisco Controller) >show redundancy summary Type of the Unit = Secondary
To configure via the GUI go to Controller / then at the bottom select HA SKU secondary unit - select enabled and reboot
2504 EOL - End of Life Status
At the time of writing (September 2016) I could not find any end of life announcement for the Cisco 2504 wireless controller. It is a little workhorse and currently supports.
The current suggested cisco wlc 2504 firmware is 220.127.116.11
It will support up to the latest firmware of 18.104.22.168.
For the latest firmware information - please refer to this link