The Challenge of AP Rejoining After Scheduled Downtime | Troubleshooting Guide
Question
After a scheduled downtime of your 5508 WLC, you notice that only a handful of the 100 APs are rejoining the controller.
All the APs are in the same subnet and use default settings.
Cisco WLC debugs indicate that the APs are sending discovery and join requests.
Only after shutting down all the switch ports that connect to the APs and turning five ports back on at a time can you rejoin all the APs.
Why were the APs unable to rejoin the Cisco WLC, and how can you prevent this from happening in the future?
Answers
Explanations
Click on the arrows to vote for the correct answer
A. B. A. D. E. D. G.B.
The correct answer to this question is A. Having all the APs in the same VLAN created a Layer 2 broadcast storm, preventing the APs from receiving discovery and join responses from the Cisco WLC.
A Layer 2 broadcast storm occurs when a large number of broadcast packets are transmitted on a network, causing network congestion and potentially bringing the network to a halt. In this case, having all the APs in the same VLAN likely caused a large number of broadcast packets to be transmitted, creating a broadcast storm that prevented the APs from receiving the necessary responses from the Cisco WLC.
To prevent this from happening in the future, one solution would be to segment the APs into different VLANs. By separating the APs into different VLANs, the broadcast traffic would be limited to each VLAN, reducing the likelihood of a broadcast storm. Another solution would be to limit the number of APs that can join the WLC at any given time, in order to avoid overwhelming the network with broadcast traffic during a large-scale deployment or upgrade.
Answer B, D, and G are incorrect. Configuring the APs to send syslog messages to a multicast or unicast address would not address the underlying issue of a broadcast storm caused by having all the APs in the same VLAN. Additionally, answer G is incorrect as there are several ways to prevent a Layer 2 broadcast storm, such as segmenting the network into smaller broadcast domains or implementing traffic shaping and rate limiting.
