This article discusses how a Dell Networking Wireless Access Point initially finds and connects to the Wireless Controller.
Verifying that the Access Point (AP) Can Connect to the Controller
Before you install APs in a network environment, you must ensure the APs are able to locate and connect to the controller.
- When connected to the network, each AP is assigned a valid IP address.
- APs are able to locate the controller
Objectives
1. Configuring Firewall Settings
2. Enabling Controller Discovery
3. Configuring DNS Resolution
4. Configuring DHCP Server Options
5. Using the Aruba Discovery Protocol (ADP)
6. Troubleshooting the Process
Configuring Firewall Settings
APs use TFTP during their initial boot to grab their software image and configuration from the controller. After the initial boot, the APs use FTP to grab their software images and configurations from the controller. Be sure to allow these transfer protocols thru your firewall to allow proper communication.
Enabling Controller Discovery
An AP can discover the IP address of the controller in the following ways:
- From a DNS server
- From a DHCP server
- Using the Aruba Discovery Protocol (ADP)
At boot time, the AP builds a list of controller IP addresses and then tries these addresses in order until a controller is reached successfully. The list of controller addresses is constructed as follows:
1. If you choose to set a DNS name, that name is resolved and all resulting addresses are put on the list. If master is set to an IP address, that address is put on the list
2. If a DNS name is not set and a controller address was received in DHCP Option, that address is put on the list.
3. If a DNS name is not set and no address was received via DHCP Option, ADP is used to discover a controller address and that address is put on the list.
4. Controller addresses derived from the server-name and the server-ip provisioning parameters and the default controller name aruba-master are added to the list.
Configuring DNS Resolution
APs are factory-configured to use the host name aruba-master for the master controller. For the DNS server to resolve this host name to the IP address of the master controller, you must configure an entry on the DNS server for the name aruba-master.
When using DNS, the AP can learn multiple IP addresses to associate with a controller. If the primary controller is unavailable or does not respond, the AP continues through the list of learned IP addresses until it establishes a connection with a controller. This takes approximately 3.5 minutes per controller.
Configuring DHCP Server Options
You can configure a DHCP server to provide the master controller's IP address. You must configure the DHCP server to send the controller's IP address using the DHCP Option 43. APs identify themselves with a vendor class identifier set to ArubaAP in their DHCP request. When the DHCP server responds to the request, it will send the controller's IP address as the value of option 43. In some cases the vendor-specific attribute is not set on the DHCP server. You will need to verify the DHCP option 60 is set to provide ArubaAP as the vendor-specific attribute presented to the AP during the DHCP request process. If Option 60 does match with ArubaAP, then the AP will ignore the IP address provided in Option 43.
When using DHCP the AP accepts only one IP address. If the IP address of the controller provided by DHCP is not available, the AP can use the other IP addresses provisioned or learned by DNS to establish a connection.
Using the Aruba Discovery Protocol (ADP)
ADP is enabled by default on all APs and Controllers. To use ADP, all APs and Controllers must be connected to the same Layer 2 network. If the devices are on different networks, a Layer-3 compatible discovery mechanism, such as DNS, DHCP, or IGMP forwarding, must be used instead.
With ADP, APs send out periodic multicast and broadcast queries to locate the master controller. You might need to perform additional network configuration, depending on whether the APs are in the same broadcast domain as the controller.
- If the APs are in the same broadcast domain as the master controller, the controller automatically responds to the APs queries with its IP address.
- If the APs are not in the same broadcast domain as the master controller, you must enable multicast on the network (ADP multicast queries are sent to the IP multicast group address 239.0.82.11) for the controller to respond to the APs queries. You must make sure that all routers are configured to listen for Internet Group Management Protocol (IGMP) join request from the controller and can route these multicast packets.
Troubleshooting
1. If the AP is not showing up in the controller as expected. Connect directly to the serial console port of the AP in order to view and log the boot process of the AP thru command line access.
2. If an AP is not receiving an IP address. Try plugging a known good laptop into the same switch port . Verify that it receives an IP address thru DHCP when requested. If the laptop receives an IP address properly then you will need to look at factory resetting the AP.
3. Once the AP receives a proper IP address, the AP must find the controller thru the steps listed above. Try pinging the IP address the AP received thru DHCP from the controller. Remember that if you are not plugging the AP into the same broadcast domain as the controller you will have to manually configure the DNS, DHCP or ADP multicast Layer 3 communication in your network environment.