Case Study: An AP Fails to Go Online Across Network Segments Due to Incorrect Option 43 Configuration

Symptom

As shown in the following figure, the AC is connected to the core switch in off-path mode. The core switch assigns IP addresses to APs, but the APs fail to go online across network segments.

Relevant Alarms and Logs

None

Cause Analysis

The AP goes online at Layer 3, and the core switch functions as the DHCP server. However, Option 43 configured on the core switch does not specify the AC's source interface.

Procedure

1. Run the following commands on the AC to check AP onboarding information.
   1. Run the display ap all command. Online APs are not on the same network segment as the source interface of the AC.
   2. Run the display ap offline-record all command. No AP going-offline records are found.
   3. Run the display ap global configuration command. The AP authentication mode is non-authentication.
   4. Run the display mac-address ap-mac command. The MAC addresses of offline APs are displayed.
   5. Run the display ip interface brief command. No VLANIF interfaces exist on the network segment where the AP resides.

2. On the core switch, check whether the source interface of the AP's MAC address is normal and whether the AP can obtain an IP address.
   1. Run the display mac-address ap-mac command. The command output shows that the source interface of the AP's MAC address is normal.
   2. Run the display arp all | include ap-mac command. The command output shows that the AP obtains an IP address successfully.

3. Test the connectivity between the gateway and the AP and between the network segment where the AP resides and the AC's source interface.
   1. Run the ping ap-ip command to check the connectivity between the gateway and the AP.
   2. Run the ping –a ap-gateway ac-capwap-ip command to check the connectivity between the AP gateway and the AC's source interface.

4. Check the DHCP configuration on the core switch.

   Run the display cur interface vlanif X command. The command output shows that Option 43 is configured.

5. Log in to the AP. Check the CAPWAP link and Option 43 in the diagnostic view.
   1. Run the display capwap link all command. The command output shows that the destination IP address is 0.0.0.0.
   2. Run the display ac-list command. The AC list is empty.

6. According to the preceding analysis, the Option 43 configuration on the core switch is incorrect, and the CAPWAP source address of the AC is not specified. Modify the Option 43 configuration on the core switch.

Suggestion and Summary

For details about configuring Option 43 on a vendor's DHCP server that connects to a Huawei AP, see How to Configure Option 43 When Huawei APs Are Connected to DHCP Servers of Different Vendors.