无线局域网控制器实现附载均衡的文档

无线局域网控制器实现附载均衡的文档

Aggressive Load Balancing on Wireless LANControllers (WLCs)

Document ID: 107457

Introduction

Prerequisites

Requirements

Components Used

Conventions

Aggressive Load Balancing

Configure Aggressive Load Balancing

Command Line Interface

Graphical User Interface

Example of Aggressive Load Balancing

Important Notes on Aggressive Load Balancing

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Related Information

Introduction

This document explains the aggressive load balancing feature on Wireless LAN Controllers (WLCs).Prerequisites

Requirements

Cisco recommends that you have knowledge of these topics:

Knowledge of how to configure the Wireless LAN Controller and lightweight access point (LAP) forbasic operation.

Basic knowledge of Lightweight Access Point Protocol (LWAPP).

Components Used

The information in this document is based on these software and hardware versions:

Cisco 4400 Series Wireless LAN Controllers that run version 5.0.148.0

Cisco Aironet 1250 Series Lightweight Access Points

Cisco Aironet 802.11a/b/g (CB21AG) Wireless LAN Client adapters that run version 3.6The information in this document was created from the devices in a specific lab environment. All of thedevices used in this document started with a cleared (default) configuration. If your network is live, make surethat you understand the potential impact of any command.

Conventions

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

无线局域网控制器实现附载均衡的文档

Aggressive Load Balancing

Aggressive load balancing on the WLC allows the LAPs to load balance wireless clients across APs in anLWAPP system. You can enable aggressive load balancing through the controller GUI or CLI.

This feature can be used in order to load balance clients across LAPs on a single controller. The clients selectthe AP based on the client Signal to Noise Ratio (SNR) to that AP and the load balancing window.Aggressive load balancing works at the association phase. If enabled and the conditions to load balance aremet, when a wireless client attempts to associate to a LAP, association response frames are sent to the clientwith an 802.11 response packet that includes status code 17. This code indicates that the AP is too busy toaccept any more associations.

It is the responsibility of the client to honor, process or discard that association response frame with reasoncode 17. Some clients ignore it, even though it is part of the 802.11 specification. The standard dictates thatthe client driver must look for another AP to connect to since it receives a "busy" message from the first AP ittries. Many clients do not do this and send the association request again. The client in question is allowed onto the wireless network upon subsequent attempts to associate.

The controller only sends one association response frame with reason code 17 to the client. If the clientdecides to discard the reason code 17, the client can try the same AP again and this time the AP allows theclient to complete the association.

If the client honors the association response status code 17, the client then attempts to associate to a differentAP. For example, if load balancing is enabled and the load balancing window is configured as five clients,when a sixth client tries to associate to the AP, the client receives an 802.11 Association Response frame withstatus code 17, which indicates that the AP is busy.

The window setting controls when aggressive load balancing starts. With a window setting of five, forexample, all clients after the sixth client are load balanced. The default load balancing window is five inversion 4.1.185.0 or later.

The clients are load balanced at the radio based on the configured load balancing window at the controller.Configure Aggressive Load Balancing

Aggressive load balancing can be configured through the CLI or the GUI on the Wireless LAN http://www.77cn.com.cnmand Line Interface

In order to enable or disable aggressive load balancing through the CLI, complete these steps:

1. Issue this command:

config load balancing status {enable | disable}

2. Issue this command in order to configure the window size:

configure load balancing window <size>

Note: The size of the window can be from zero to 20.

无线局域网控制器实现附载均衡的文档

Graphical User Interface

In order to configure aggressive load balancing through the GUI, complete these steps:

1. From the controller GUI, click Controller > General in order to open the General page.

2. From the Aggressive Load Balancing drop down box, choose either Enabled or Disabled in orderto configure this feature.

3. Click Apply.

Example of Aggressive Load Balancing

This is an example of aggressive load balancing:

Two APs, AP1 and AP2, have two and three clients associated to each, respectively.

Load balancing is enabled, and the window is set to zero.

This information is obtained from debug on the controller:

*May 19 13:10:33.023: 00:40:96:b4:8b:ff

Load Balancing mobile 00:40:96:b4:8b:ff 802.11bg minimum users 0, window 0*May 19 13:10:33.023: 00:40:96:b4:8b:ff

Load Balancing mobile 00:40:96:b4:8b:ff on AP 00:17:df:9f:0f:e0(1) band 1 has 0 users Good: rssi (antenna A 31) (antenna B 57), snr = 57

*May 19 13:10:33.023: 00:40:96:b4:8b:ff

Load Balancing mobile 00:40:96:b4:8b:ff on AP 00:17:df:9e:ad:d0(1) band 1 has 2 users Bad: rssi (antenna A 37) (antenna B 64), snr = 38

*May 19 13:10:33.023: 00:40:96:b4:8b:ff

Load Balancing mobile 00:40:96:b4:8b:ff could not find acceptable 802.11a candidate defaulting all

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