The most frequent cause is a WAN interface (DHCP or PPPoE) that is automatically pulling DNS settings from your ISP. These ISP servers often fail to resolve the required globalddns.fortinet.net domain.
: Next, test your FortiGate's ability to resolve the specific domain names used for FortiGuard services: The most frequent cause is a WAN interface
If all else fails, consider upgrading the FortiGate to the latest stable version of FortiOS. Firmware updates often include fixes for known bugs related to FortiGuard connectivity and DDNS functionality. This is particularly relevant for older versions such as 5.2.x or 6.0.x, which are known to have limitations. Firmware updates often include fixes for known bugs
In newer FortiOS versions, FortiGate uses by default to locate the closest FortiGuard server. While efficient, Anycast can fail if regional routing paths are unstable or if certain server nodes are down. Disabling Anycast forces the FortiGate to use traditional, server-list-based routing. While efficient, Anycast can fail if regional routing