
Availability and Session Availability
SCALANCE WLC711
User Guide, V8.11, 07/2012, C79000-G8976-C260-03 12-3
SCALANCE IWLAN Controller, so that they may re-register with their home SCALANCE
IWLAN Controller. Foreign APs can now all be released at once by using the Foreign button on
the Access Approval screen to select all foreign APs, and then clicking Release.
To support the availability feature during a failover event, you need to do the following:
1. Monitor the critical messages for the failover mode message, in the information log of the
remaining SCALANCE IWLAN Controller (in the Logs & Traces section of the SCALANCE
W Wireless Assistant).
2. After recovery, on the SCALANCE IWLAN Controller that did not fail, select the foreign
Wireless APs, and then click Release on the Access Approval screen.
Availability Prerequisites
Before you configure availability, you must do the following:
• Choose the primary and secondary SCALANCE IWLAN Controllers.
• Verify the network accessibility for the UDP connection between the two controllers. The
availability link is established as a UDP session on port 13911.
• Set up a DHCP server for AP subnets to support Option 78 for SLP, so that it points to the IP
addresses of the physical interfaces on both the SCALANCE IWLAN Controllers.
• Ensure that the Poll Timeout value on the AP Properties tab Advanced dialog is set to 1.5 to 2
times of Detect link failure value on the SCALANCE IWLAN Controller > Availability
screen. For more information, see “Configuring a Wireless AP’s Properties” on page 3-21.
If the Poll Timeout value is less than 1.5 to 2 times of Detect link failure value, the Wireless
AP failover will not succeed because the secondary controller will not be 'ready' to accept the
failover APs.
On the other hand, if the Poll Timeout value is more than 1.5 to 2 times of Detect link failure
value, the Wireless APs failover will be unnecessarily delayed, because the Wireless APs will
continue polling the primary controller even though the secondary controller is ready to
accept them as the failover APs.
• To achieve ideal availability behavior, you must set the Poll Timeout value for all Wireless
APs to 15 seconds, and the Detect link failure on the SCALANCE IWLAN Controller >
Availability screen to ten seconds.
Configuring Availability Using the Availability Wizard
The availability wizard allows you to create an availability pair from one of the SCALANCE
IWLAN Controllers that will be in the availability pair. When creating the availability pair, you
also have the option to synchronize VNS definitions and GuestPortal user accounts between the
paired SCALANCE IWLAN Controllers.
To Configure Availability Using the Availability Wizard:
1. From the top menu, click Wireless Controller. The SCALANCE IWLAN Controller
Configuration screen is displayed.
2. In the left pane, click Availability. The availability configuration screen is displayed.
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