AP at a certain site cannot register and reports the error "Unsupported discovery type"

AC and AP Layer 2 Networking

The AP uses Layer 2 registration. The AP address is obtained normally. The AC and AP can ping each other, but the AP cannot register with the AC.

Let's troubleshoot according to the general routine:

1. First check the configuration. The basic configuration of AP registration is correct and the serial number is also correct.

2. AP can obtain the address normally, and AC and AP can ping each other.

3. Debug wlan capwap on AC and AP at the same time to collect information. According to the AP registration process, see which stage is stuck. First, let's look at the debug information of the AP:

*Jan 1 00:03:26:362 2014 H3C CWC/7/FSM: Enter Discovery state.

*Jan 1 00:03:26:363 2014 H3C CWC/7/EVENT: Fill discover req.wtu=1.model=WAP722S.wt drv info:[].subslot=0.licensetype=1.ret=0x40010001.

*Jan 1 00:03:26:363 2014 H3C CWC/7/EVENT: Fill discover req.ap=1.model=WAP722S.licensetype=1.carry wt info is unnecessary.

*Jan 1 00:03:26:364 2014 H3C CWC/7/SND_PKT: Sent discovery request with SeqNum 0 to AC 255.255.255.255:5246. *Jan 1 00:03:26:364 2014 H3C CWC/7/SND_PKT: Verbose info for discovery request sent to AC 255.255.255.255:5246, length=155. .... ............ *Jan 1 00:03:26:365 2014 H3C CWC/7/SND_PKT: Sent discovery request with SeqNum 0 to AC 224.0.1.140:5246. *Jan 1 00:03:26:365 2014 H3C CWC/7/SND_PKT: Verbose info for discovery request sent to AC 224.0.1.140:5246, length=155. ........................ *Jan 1 00:03:26:365 2014 H3C CWC/7/TMR: [AP 1] Create Max Discovery Interval Timer. *Jan 1 00:03:32:360 2014 H3C CWC/7/TMR: MaxDiscovery Interval r expired. *Jan 1 00:03:32:361 2014 H3C CWC/7/EVENT: Fill discover req.wtu=1.model=WAP722S.wt drv info:[].subslot=0.licensetype=1.ret=0x40010001. *Jan 1 00:03:32:361 2014 H3C CWC/7/EVENT: Fill discover req.ap=1.model=WAP722S.licensetype=1.carry wt info is unnecessary.

According to the debug information of the AP, the AP has been sending discovery messages to the AC, but has not received any response messages from the AC. It may be that the AP has not actually forwarded the message from the port, or there may be a problem in the intermediate link that causes the AP to not receive the response message from the AC.

4. Let's see what the debug information collected from the AC shows.

*Jun 12 21:26:27:267 2019 H3C CWS/7/RCV_PKT: Received discovery request with SeqNum 0 from AP at 10.xxx.2.xxx:58629. xxx:58629, Length=155. ........................ *Jun 12 21:26:27:267 2019 H3C CWS/7/EVENT: usApcbConnectingCnt is 0. *Jun 12 21:26:27:267 2019 H3C CWS/7/ERROR: Failed to process discovery request from AP with serial ID 21980xxxxxxxxxxx2Z: Unsupported discovery type.

*Jun 12 21:26:27:267 2019 H3C CWS/7/ERROR: Failed to proc pkt msg from AP at 10.xxx.2.xxx:1509. MsgType = 1.

From the AC debug, we can see that the AC received the discovery request from the AP, but an error message appeared on the AC: Failed to process discovery request from AP with serial ID 21980xxxxxxxxxxx2Z: Unsupported discovery type. It seems that the AC does not support the format of the AP discovery request.

Let's look back at the AC configuration to see if there are any special commands. At this time, we found the following command in the AC configuration:

 #

wlan capwap discovery-policy unicast

 #

Usually, the AP can discover the AC and establish a CAPWAP or LWAPP tunnel through unicast, multicast and broadcast. Configuring this command means enabling the unicast discovery policy function. The AC only responds to APs that send unicast Discovery request messages, and does not respond to APs that send multicast or broadcast Discovery request messages. That is, only unicast discovered APs are allowed to establish CAPWAP or LWAPP tunnel connections with AC.

From here we have found the root cause of the problem. The AP broadcasts a request to the AC. Since the AC has enabled the unicast discovery policy function, the AC does not respond to the AP, so the AP cannot register.

Delete the wlan capwap discovery-policy unicast command to solve the problem.