Users Guide

Dell PowerConnect ArubaOS 5.0 | User Guide The Basic User-Centric Networks | 51
Locating the Controller
An AP can discover the IP address of the controller in the following ways:
z From a DNS server
z From a DHCP server
z Using the Dell 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 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.
2. 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.
3. 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.
4. 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.
This list of controller IP addresses provides an enhanced redundancy scheme for controllers that are located in
multiple data centers separated across Layer-3 networks.
From a DNS Server
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.
For information on how to configure a host name entry on the DNS server, refer to the vendor documentation for
your server.
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 an available controller. This takes approximately 3.5 minutes per LMS.
From 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. APs identify
themselves with a vendor class identifier set to Dell AP 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.
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 Appendix A, “”
or
refer to the vendor documentation for your server.
Note: Dell 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.