这篇随笔主要记录的是Apple设备连接思科无线可能出现的问题，尤其是在思科WLC3504下部署的无线网络，这种故障体现的尤为明显。
For Single SSID
To support Apple iOS-based devices (iPhone/iPad) switching from one SSID to another on the same wireless access point, configure the Wireless LAN Controller (WLC) to enable the “FAST SSID change” function. This function helps ensure iOS-based devices are able to more quickly switch between SSIDs.
For Dual SSID BYOD
Fast SSID must be enabled to support dual SSID BYOD. When Fast SSID changing is enabled, the wireless controller allows clients to move faster between SSIDs. When fast SSID is enabled, the client entry is not cleared and the delay is not enforced. For more information about configuring Fast SSID on a Cisco WLC,
1、场景
WLC版本：8.5.131
WLC型号：AIR-CT3504-K9
2、示例
假设在该无线网络下存在多个SSID，如果连接一个，再尝试连接另一个，可能会出现“无法连接该网络”/ "Unable to join the network SSID-name"
如下是一个例子，从RSCCIEW的SSID切换到TEST时出现的问题：
如果收集debug client xx.xx.xx.xx.xx.xx
可能会获取到如下信息：
(WLC1) >*apfMsConnTask_0: Jun 05 13:56:04.571: 54:26:96:3e:4b:ee Association received from mobile on AP 00:22:bd:98:3a:30
*apfMsConnTask_0: Jun 05 13:56:04.572: 54:26:96:3e:4b:ee Deleting client immediately since WLAN has changed
*apfMsConnTask_0: Jun 05 13:56:04.572: 54:26:96:3e:4b:ee Scheduling deletion of Mobile Station: (callerId: 50) in 1 seconds
*apfMsConnTask_0: Jun 05 13:56:04.883: 54:26:96:3e:4b:ee Ignoring 802.11 assoc request from mobile pending deletion
3、解决方法
通过在WLC上开启FAST SSID Change，该功能默认是关闭的。
When fast SSID changing is enabled, the controller allows clients to move between SSIDs. When the client sends a new association for a different SSID, the client entry in the controller connection table is cleared before the client is added to the new SSID. When fast SSID changing is disabled, the controller enforces a delay before clients are allowed to move to a new SSID.
当FAST SSID Change开启是，控制器允许客户端在SSID之间移动，这种情况下是当客户端发送一个新的关联信息到一个不同的SSID时，控制器上的客户端连接条目在该客户端连接到另一个SSID之前就会立即被清除掉。而当FAST SSID Change被关闭时，在客户端移动到一个新的SSID之前WLC会让这个操作延迟。
操作步骤：
3.1 登录WLC的GUI，打开General界面
3.2 在Fast SSID Change下拉框选择enable
3.3 点击apply
3.4 点击Save Configuration保存配置
通过命令行开启：
(WLC1) >config network fast-ssid-change ?
enable/disable] Enable or disables fast SSID changing for mobile stations
(WLC1) >config network fast-ssid-change enable
(WLC1) >save config
Are you sure you want to save? (y/n) y
Configuration Saved!
4、这个问题还可能伴随一个问题，WPA+WPA2 参数的问题。
对于WPA和WPA2最好按照如下设置：
WPA+TKIP
WPA2+AES
最好不要混用。