AP L2 registration failed at a certain site

Normal topology, AP L2 registration

AP L2 registration fails to come online

AP Layer 2 registration does not go online, and from experience, the probability is that it is a configuration problem or a network link problem. We follow the general AP registration process for troubleshooting. 

1, first confirm that the AP is automatically registered or configured AP template on the AC, if the configuration is AP template, you need to check whether the template configuration is incorrect. 

2, whether the AP can get an IP address, if not, you need to check the dhcp server configuration and the interaction of dhcp messages. 

3, in the case of the AP to get the IP address, AP and AC interoperability, you can use ping test, if not, you need to check the intermediate link connectivity. 

4, to confirm that there is only one AC adapted to the network, because it is a two-layer registration, the AP sends broadcast messages in the network, if there are more than one AC in the layer 2 network, it is likely that the AP has been registered to the other AC. 

5, the above troubleshooting are not a problem, you can capture packets or debug, look at the AP's capwap message interaction. After collecting packet capture, found that only the AP sent a broadcast request, but no AC response. 

Let's take a look at the configuration of the AC. After checking the configuration of the AC, we found that there is a special command on the AC: wlan capwap discovery-policy unicast Enable unicast discovery policy function The AP can discover the AC and establish CAPWAP or LWAPP tunnels in three ways: unicast, multicast, and broadcast. After you enable the unicast discovery-policy function, the AC responds only to APs that send unicast Discovery request messages and does not respond to APs that send multicast or broadcast Discovery request messages, i.e., only unicast-discovered APs are allowed to establish a CAPWAP or LWAPP tunnel connection with the AC. 

By now the problem has been identified, which is caused by this command. By default the feature is turned off, i.e., the AC responds to broadcast requests. 

Execute the following command:

undo wlan capwap discovery-policy