Enable Controller Discovery

An AP can discover the IP address of the controller from a DNS server, from a DHCP server, or 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 it successfully reaches a controller . This list of IP addresses provides an enhanced redundancy scheme for controllers that are located in multiple data centers separated across Layer-3 networks. The AP constructs its list of controller addresses as follows:

If the master provisioning parameter is set to 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.
If the master provisioning parameter is not set and a controller address was received in DHCP Option 43, that address is put on the list.
If the master provisioning parameter is not set and no address was received via DHCP option 43, ADP is used to discover a controller address and that address is put on the list.
Controller addresses derived from the server-name and server-ip provisioning parameters and the default controller name aruba-master are added to the list. Note that if a DNS name resolves to multiple addresses, all addresses are added to the list.

Controller Discovery using DNS

When using DNS, AP learns 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 an available controller. This takes approximately 3.5 minutes per controller.

 

Aruba recommends using a DNS server to provide APs with the IP address of the master controller because it involves minimal changes to the network and provides the greatest flexibility in the placement of APs.

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.

Controller Discovery using ADP

ADP is enabled by default on all Aruba APs and controllers. With ADP, APs send out periodic multicast and broadcast queries to locate the master controller. ADP requires that all APs and controllers are connected to the same Layer-2 network. If the devices are on different networks, you must use a Layer-3 compatible discovery mechanism, such as DNS, DHCP, or IGMP forwarding.

To use ADP discovery:

1. Issue the command show adp config to verify that ADP and IGMP join options are enabled on the controller, If ADP is not enabled, you can reenable ADP using the command adp discovery enable and adp igmp-join enable.
2. If the APs are not in the same broadcast domain as the master controller, you 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 also must make sure that all routers are configured to listen for Internet Group Management Protocol (IGMP) join requests from the controller and can route these multicast packets. C

Controller discovery using a DHCP Server

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 vendor-specific attribute option 43. The APs identify themselves with a vendor class identifier set to ArubaAP in their DHCP requests. When the DHCP server responds to a request, it will send the controller’s IP address as the value of option 43.

When using DHCP option 43, 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. For more information on how to configure vendor-specific information on a DHCP server, see “DHCP with Vendor-Specific Options” on page 1 or refer to the documentation included with your server.