Cisco AIR-WLC2006-K9 - Wireless LAN Controller 2006 Betriebsanweisung PDF herunterladen (Seite 51)

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Cisco Wireless LAN Solution Product Guide

OL-7955-01

Chapter 1 Overview

Cisco Wireless LAN Controllers

Cisco Wireless LAN Controller Failover Protection

Each Cisco Wireless LAN Controller has a defined number of communication ports for Cisco 1000

series lightweight access points. This means that when multiple controllers with unused access point

ports are deployed on the same network, if one controller fails, the dropped access points automatically

poll for unused controller ports and associate with them.

During installation, Cisco recommends that 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 WLAN Solution Mobility Group information.

During failover recovery, the configured lightweight access points obtain an IP address from the local

DHCP server (only in Layer 3 Operation), attempt to contact their primary, secondary, and tertiary

controllers, and then attempt to contact the IP addresses of the other controllers in the Mobility group.

This prevents the access points from spending time sending out blind polling messages, resulting in a

faster recovery period.

In multiple-controller deployments, this means that if one controller fails, its dropped access points

reboot and do the following under direction of the Radio Resource Management (RRM):

• Obtain an IP address from a local DHCP server (one on the local subnet).

• If the Cisco 1000 series lightweight access point has a primary, secondary, and tertiary controller

assigned, it attempts to associate with that controller.

• If the access point has no primary, secondary, or tertiary controllers assigned or if its primary,

secondary, or tertiary controllers are unavailable, it attempts to associate with a master controller on

the same subnet.

• If the access point finds no master controller on the same subnet, it attempts to contact stored

Mobility Group members by IP address.

• Should none of the Mobility Group members be available, and if the Cisco 1000 series lightweight

access point has no Primary, Secondary, and Tertiary Cisco Wireless LAN Controllers assigned and

there is no master Cisco Wireless LAN Controller active, it attempts to associate with the

least-loaded Cisco Wireless LAN Controller on the same subnet to respond to its discovery

messages with unused ports.

This means that when sufficient controllers are deployed, should one controller fail, active access point

client sessions are momentarily dropped while the dropped access point associates with an unused port

on another controller, allowing the client device to immediately reassociate and reauthenticate.

Cisco Wireless LAN Controller Automatic Time Setting

Each controller can have its time manually set or can be configured to obtain the current time from one

or more Network Time Protocol (NTP) servers. Each NTP server IP address is added to the controller

database. Each controller searches for an NTP server and obtains the current time upon reboot and at

each user-defined polling interval (daily to weekly).

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Cisco AIR-WLC2006-K9 - Wireless LAN Controller 2006 Betriebsanweisung Seite 51