Understanding Master AP Election

 

Q: How do I identify which AP is the Master AP?

A: The CTL LED of the Master AP is solid green all the time. On the Unleashed web UI, the Master AP is marked as shown in the following figure. The Unleashed Mobile app provides a similar icon to denote the Master AP.

Figure 1. Master AP




A: An AP can be set to never become a Master using the AP CLI. To configure an AP to always assume the role of member, SSH to that AP and issue the following AP CLI command:

set election role 1

To clear the setting, use the following AP CLI command:

set election role 0

Figure 2. Set election role

Q: Is it possible to designate a specific Unleashed AP as the Master AP?

A: Starting with release 200.5, you can configure an AP to be the "preferred Master." Prior to release 200.5, the only option was to set all other APs as Member APs via CLI command. By default, without any specific configuration, Unleashed APs automatically elect the most appropriate AP to be the Master AP.

Q: What will happen if the Master AP is disconnected or goes down?

A: Once Unleashed APs fail to contact the Master for 30 seconds, the election mechanism will start and a new Master AP will be elected. During this period of time, existing wireless clients may remain connected but no new clients can associate with the WLAN.

The exception is if the Gateway function is enabled (only possible on the Master AP). In this case, Master AP election will not happen because the Gateway AP needs a physical WAN connection and no other APs can automatically replace it.

Q: In case the Master AP is disconnected, how long will it take for the Unleashed Network to resume operation?

A: The WLAN service is impacted for about 80 seconds, however Member APs will only have WLAN downtime for a few seconds.

Once APs lose connection to the Master AP for 30 seconds, the new Master AP election starts. Afterwards member APs will join this new Master AP and receives configuration from it. The process takes about 40 seconds. However, even if a Member AP loses its connection to the Master, the existing WLAN service continues, although new clients will not be authenticated during this period of time. When a new Master AP is elected, a Member AP will experience WLAN down time for a few seconds before normal operation is resumed.

Q: Will the old configuration be lost if the Master AP is disconnected from the network?

A: No. For Unleashed 200.2 and later releases, all member AP's keep a copy of the configuration, and when a new AP is elected as the master, it restores the configuration from this copy.

In Unleashed 200.0 and 200.1 releases, the Standby Master AP stores the configuration, and it may take the Master AP role if it loses connection to the Master AP.

Q: What are the Master AP election criteria?

Q: Can a Mesh AP be elected as the Master AP?

A: A Mesh AP, which has no Ethernet connection for uplink, cannot assume the role of Master AP.

Q: I cannot see any Unleashed web interface displayed in my browser. It seems there is no AP assuming the role of Unleashed Master AP. How do I investigate the situation?

A: Make sure the administrative PC is on the same network as the Unleashed Master AP (or connected to an Unleashed SSID), and enter the following URL http://unleashed.ruckuswireless.com in your browser. You should be redirected to the Unleashed web UI.

Note that if mesh is enabled on your network, only Root APs (i.e., APs connected to the Internet through a wired interface) can become the Unleashed Master AP. One of the criteria to become the Root AP is that an AP can contact its gateway through a wired interface. Therefore, if your network's default gateway becomes unreachable, none of the Unleashed APs can become the Root AP of the mesh network, and then there will be no Unleashed Master on your network. The exception to the above is when the gateway function is enabled; in this case the Gateway AP is the Master AP regardless of whether mesh is enabled, or whether its gateway is reachable or not.

If the above doesn't apply to your situation, figure out any AP's IP address, and enter "http://<any AP IP address>" in the URL bar of your browser to access the Unleashed web interface.

If there is still no response (and one of the APs' IP addresses is known), you can SSH into the AP and perform the following:

Type the "get election" AP CLI command. It shows the status of all Unleashed APs, and should display one AP marked as Master. Ping that AP's IP address from a device connected to the same network. If the AP is not reachable, maybe there is an access denial policy configured on your network in one of your devices. If the AP is responding, type that AP's IP address in a browser's URL bar and check whether the Unleashed web UI can be displayed.

Figure 3. "get election" CLI command

If mesh is enabled, issue get mesh to check the mesh status. Only an AP in "ROOT" mesh mode can be the Master AP.

If everything looks fine, but the network still doesn't seem to have an AP assuming the Master role, you may need help from Ruckus customer support. Follow the issue reporting procedure described at the beginning of this document to report the problem.

Q: What will happen if a disconnected Master AP is reconnected back to the network after a new Master has been elected?

A: The two Master APs will communicate with each other to elect one AP to serve as the Master, and the other AP will become a Member AP and join the master.

Q: How do I enable debugging logs for Master election?

A: Go to Admin & Services > Administer > Diagnostics > Debug Info, and enable the Auto Election debug component.

Figure 4. Select Auto Election

Alternatively, SSH to an Unleashed AP and manually turn on election log debugging on that particular AP using the following AP CLI command:

set election debug X

where X is a number representing the debug level: 1 means to only show messages in case of error. 8 means generate all messages for debugging purposes.

Figure 5. Use "set election debug 8" to generate all messages