Техническая Инструкция для Cisco Cisco 2000 Series Wireless LAN Controller

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.

This configuration can also be used with any other Cisco WLC and any lightweight AP.

Refer to Cisco Technical Tips Conventions for more information on document conventions.

Refer to WLAN Controller Failover for Lightweight Access Points Configuration Example for information on
how to configure the WLC and lightweight AP for failover.

You can perform AP load balancing on two (or more) WLCs if you configure mobility groups properly. The
LWAPP allows for dynamic redundancy and load balancing. For example, if you specify more than one IP
address for option 43, an AP sends LWAPP discovery requests to each of the IP addresses that the AP
receives. In the WLC LWAPP discovery response, the WLC embeds this information:

Information on the current AP load, which is defined as the number of APs that are joined to the WLC
at the time

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The AP capacity

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The number of wireless clients that are connected to the WLC

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The AP then attempts to join the least loaded WLC, which is the WLC with the greatest available AP
capacity. After an AP joins a WLC, the AP learns the IP addresses of the other WLCs in the mobility group
from its joined WLC.

Subsequently, the AP sends LWAPP primary discovery requests to each of the WLCs in the mobility group.
The WLCs respond with a primary discovery response to the AP. The primary discovery response includes
information about the WLC type, total capacity, and current AP load. As long as the WLC has the AP
Fallback parameter enabled, the AP can decide to change over to a less loaded WLC.

When the AP boots or resets, it only knows the controller management IP addresses from DNS
(Cisco−lwapp−controller@local_domain.com) (20 max), DHCP option 43 (20 max), OTAP,
255.255.255.255, and the previously joined controller. The controllers in the mobility group of the previously
joined controller are not retained across reboots.

However, if the AP loses connectivity with the controller, it does not reboot. It moves directly into discovery
mode and remembers the mobility group members. It can then send a discovery request to all members of the
mobility group.

Note: Once an AP joins a controller, it only leaves the currently joined controller for a limited number of
reasons. One reason that the AP does not leave the currently joined controller is if the APs are not exactly load
balanced across all controllers. For that reason, this load balancing algorithm is only an approximate load
balancing algorithm unless you manually define a primary controller for each AP.