This document explains how to set up multiple wireless LAN (WLAN)
controllers (WLCs) for a failover condition. A failover condition occurs when a
primary controller goes down or fails for any reason. Then, a second controller
takes over the operation. Failover is also called controller redundancy.
Ensure that you meet these requirements before you attempt this
Basic knowledge of the configuration of lightweight access points
(APs) and Cisco WLCs
Basic knowledge of Lightweight AP Protocol (LWAPP)
Knowledge of the configuration of an external DHCP server
The information in this document is based on these software and
Cisco Aironet 1000 Series Lightweight AP
Two Cisco 2000 Series WLCs that run firmware 22.214.171.124
Microsoft Windows Server 2003 Enterprise DHCP
This configuration works with any other Cisco WLC and any lightweight
The information in this document was created from the devices in a
specific lab environment. All of the devices used in this document started with
a cleared (default) configuration. If your network is live, make sure that you
understand the potential impact of any command.
Technical Tips Conventions for more information on document
This document uses this network setup.
Two Cisco 2006 WLCs and a lightweight AP are connected through a hub.
An external DHCP server is also connected to the same hub. All the devices are
in the same subnet. The AP is initially registered to the primary controller.
You must configure the lightweight AP and the WLC so that the AP automatically
switches to the secondary controller if the primary controller goes down. You
also must ensure that the AP registers back to the primary controller after the
AP is back on line. In order to ensure that the AP registers back to the
primary controller, you should use the mobility groups and the AP fallback
features of the WLCs.
Note: Before you configure the controller for failover of access points,
you must configure the WLC for basic operation and register the LAPs to the
WLC. This document assumes that the WLC is configured for basic operation and
that the LAPs are registered to the WLC. If you are a new user and need to
register a LAP with a controller, refer to
AP (LAP) Registration to a Wireless LAN Controller (WLC).
In order to configure the devices for WLC failover (or redundancy), you
must complete these steps:
Configure mobility groups for the
Assign primary, secondary, and tertiary
controllers for the lightweight AP .
Configure the Fallback feature on
You can configure a set of WLCs as a mobility group in order to allow
seamless client roaming within a group of WLCs. If you create a mobility group,
you can enable multiple WLCs in a network in order to provide redundancy in the
event that a WLC goes down. If a WLC goes down, all the APs that are registered
to that WLC automatically switch to the other WLCs in the mobility group. When
the primary controller comes back on, the APs fall back to it. However, this
operation takes 30 seconds. During this period of time, the service to the APs
is interrupted as the APs rejoin the primary WLC.
Note: The mobility group name configured must be the same on all the
controllers that belong to a particular mobility group. The mobility group name
is also case sensitive. Also, the mobility group members list configured on
each controller should contain all the controllers of that particular mobility
group. These configurations ensure that the failover occurs seamlessly. These
configurations also ensure that when the primary controller comes back on, the
previously registered APs fall back to it.
Note: In addition, make sure that the wireless (WLAN) configurations are
similiar on both the primary and secondary WLCs so that the client roaming is
This setup configures the two WLCs to form a mobility group. In order
to configure mobility groups, complete these steps:
From the GUI, click the Controller tab in the menu
at the top of the window, and then choose Mobility Groups from
the menu on the left.
The Static Mobility Group Members window appears. In this window,
you can define new mobility groups or edit existing mobility
Create a new mobility group for the WLCs that you have in your
This example has only two WLCs.
Define the mobility group member IP and MAC addresses, and the
This example provides the IP address 172.16.1.50 and the MAC
address of the second WLC, 00:0b:85:33:52:80, and defines the mobility group
name as Test.
Here is an example:
Ping from the GUI in order to check the reachability of the group
The ping function is in the top right menu. A popup window appears
with the reply.
Repeat these steps on the second WLC in order to configure the mobility
group. The mobility group name must be the same on both WLCs, and it is case
sensitive. Mobility groups are useful for features such as intercontroller
roaming and intracontroller roaming. For more information on these features,
refer to the
of Mobility Groups
Next step in this configuration is to define the primary, secondary,
and tertiary controllers on the lightweight AP. This assignment decides the
order in which the APs choose the controllers. Complete these
From the GUI, click the Wireless tab in the menu
at the top of the window, select the AP from the list of APs that are
registered to the WLC, and click Detail beside the
The All APs > Details window
In this window, define the primary, secondary, and tertiary
Note: Define only system names under the primary, secondary, and
tertiary controller name fields. Do not enter the IP address or the MAC address
of the controller in these fields.
Note: This example does not add a tertiary controller name because
there are only two controllers.
The last step is to configure the Fallback feature on the controller.
This feature ensures that the AP switches return to the first WLC when the WLC
that comes back on line. Complete these steps:
From the GUI, choose Controller >
A list of options appears on the General screen.
For the AP Fallback option, choose Enabled from
the drop-down menu.
Note: It is sufficient to enable the Fallback feature on the secondary
controller alone. But it is recommended to configure it on the primary WLC as
well because it can be configured as a secondary controller for other access
After you complete these steps, the setup is configured for WLC
failover. When the primary controller (WLC-1, in this case) goes down, the APs
automatically get registered with the secondary controller (WLC-2). The APs
register back to the primary controller when the primary controller comes back
on line. AP switching between the primary and secondary controllers also
affects the wireless clients associated with these APs.
In controller software release 126.96.36.199, you can configure the
wireless network so that the backup controller recognizes a join request from a
higher-priority access point and, if necessary, disassociates a lower-priority
access point as a means to provide an available port. In order to configure
this feature, failover priority must be enabled on the network and assign
priorities to the individual access points. By default, all access points are
set to priority level 1, which is the lowest priority level.
Note: Be aware that Failover priority takes effect only if there are more
association requests after a controller failure than there are available backup
Wireless LAN Controller Failover Priority
During installation, Cisco recommends you connect all lightweight
access points to a dedicated controller, and configure each lightweight access
point for final operation. This step configures each lightweight access point
for a primary, secondary, and tertiary controller and allows it to store the
configured mobility group information. When sufficient controllers are
deployed, if one controller fails, active access point client sessions are
momentarily dropped while the dropped access point associates with another
controller, which allows the client device to immediately reassociate and
Use this section to confirm that your configuration works properly.
Output Interpreter Tool
(registered customers only)
(OIT) supports certain
show commands. Use the OIT to view an analysis of
show command output.
You can verify if the configuration works as expected. Power down the
primary controller to which the AP is currently registered. The AP waits for
the heartbeat time set, which is 30 seconds by default, to detect the failure
of the primary WLC. After this period of time, the AP sends heartbeat messages
seven more times, one per second, in efforts to find the primary WLC. If the AP
does not hear from the primary WLC, the AP registers to an available WLC via
the default process. Therefore, the process to detect the primary WLC failure
and register to the secondary WLC takes approximately 80 seconds. Once the
access point joins the secondary controller, it continues to send the discovery
request to the primary controller in order to determine if the primary
controller is back in operation. This can be determined with the help of the
debug lwapp client packet command.
Note: The heartbeat message is similar to a keepalive message. The AP
heartbeat is set to 30 seconds by default. You can adjust this heartbeat time,
down to 1 second. However, if you have not made this adjustment since the last
time that the AP heard from the WLC, 30 seconds pass before the AP realizes
that it cannot reach the WLC.
This example shows that the AP gets registered to the secondary
When the primary controller (WLC-1) comes back on line, the AP again
switches back to the primary controller. Here is an
You can also use the show ap summary command
on the WLC in order to view the APs that are registered to the WLC. Here is an
Note: If the global 802.11g configuration between the controllers does not
match (enable versus disable), when you run 5.2 code or later on WLCs and set
up AP high availability, it can cause AP join issues when a failover event
occurs. Make sure that all WLC settings are identical between
Use this section to troubleshoot your configuration.
Note: Refer to
Information on Debug Commands before you use
The debug lwapp client packet command
output shows the discovery request sent by the access point to the primary
Cisco Controller) > debug lwapp client packet
*Feb 25 02:12:55.743: Sent Msg Type : ECHO_REQUEST
*Feb 25 02:12:55.743: Msg Length : 12
*Feb 25 02:12:55.743: Msg SeqNum : 48
*Feb 25 02:12:55.744: Sent Msg Type : PRIMARY_DISCOVERY_REQ
*Feb 25 02:12:55.744: Msg Length : 27
*Feb 25 02:12:55.744: Msg SeqNum : 0
*Feb 25 02:12:55.744: Recd Msg Type : ECHO_RESPONSE
*Feb 25 02:12:55.744: Msg Length : 0
*Feb 25 02:12:55.745: Msg SeqNum : 48
*Feb 25 02:12:55.745: LWAPP_CLIENT_PACKET_DEBUG: SPAM received ECHO_RESPONSE
*Feb 25 02:12:55.745: Recd Msg Type : PRIMARY_DISCOVERY_RES
*Feb 25 02:12:55.746: Msg Length : 27
*Feb 25 02:12:55.746: Msg SeqNum : 0
*Feb 25 02:12:55.746: LWAPP_CLIENT_PACKET_DEBUG: SPAM received PRIMARY_DISCOVERY_RES
You can use these additional debug commands
in order to troubleshoot your configuration:
debug lwapp events enable—Shows the series
of steps involved when lightweight access point register to a controller.
debug lwapp errors enable—Configures the
debug of LWAPP errors.
debug dhcp message enable—Configures the
debug of DHCP messages that are exchanged to and from the DHCP
debug dhcp packet enable—Configures the
debug of DHCP packet details that are sent to and from the DHCP
In some cases, LWAPP APs in the same mobility group are seen as rogue
APs by another WLC. This is because of Cisco bug ID
(registered customers only)
. This can happen in one of two
The AP sees more than 24 neighbors. The neighbor list size is 24, so
any other neighbors are reported as rogues.
AP1 can hear a client that communicates to AP2, but AP2 cannot be
heard and therefore cannot be validated as a
The workaround is to manually set the APs to known
internal on the WLC and/or WCS.
Complete these steps on the controller in order to manually set the APs
to known internal.
Go to the WLC GUI, and choose
Click on the Rogue Aps in the left side
From the Rogue-AP list, choose
From the Update Status menu choose Known
internal, and click Apply.