FortiWLC – Option 43

Option 43

Option 43 is not part of any Fortinet product; it is a method for mapping controllers. With DHCP Option 43, you can specify a primary and backup controller for APs. With this configuration, the backup controller can be in a different subnet from the primary controller. Option 43 implements redundancy by specifying which controllers (primary and secondary) an AP should associate to. This feature is supported across all access points. A backup controller can be configured using either DHCP or DNS.

Option 43

For example, using Option 43, if “wlan-controller” is mapped to P1 (and P1 has a redirect to P2) and “wlan-controller-2” is mapped to S1 (and S1 has a redirect to S2), the discovery order would be P1, P2, S1, S2. If a controller has both a DNS entry and Option 43 enabled, the AP will first use the host address as configured on the AP (default value = wlan-controller). If the host address is configured as or if the host is a name and the name cannot be resolved using DNS, only then will the AP look at the DHCP Option 43 value. For specific Option 43 configuration directions, see the Support Portal How-To 4062-125.

AP Aware Redundancy using DHCP Option 43
  • Configure APs with L3 preferred and the controller name as
  • On the DHCP server, Option 43 values need to be configured with primary and secondary controller IPs and/or hostnames. Then, when an AP contacts the DHCP server to obtain an IP address, it also receives primary and secondary controller IP information using the Option 43 value from the DHCP server.
AP Aware Redundancy using DNS
  • Configure APs with L3 preferred and the controller name as the hostname of the controller.
  • Configure a DNS entry to resolve the primary hostname on the DNS server. Configure a DNS entry to resolve the secondary hostname on the DNS server.
  • Configure the hostname of the primary controller on the AP with L3 preferred mode.

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