Want to show DNS requests that failed to resolve

Hi gurus,

I'm using DNS server on the Fortigate (config system dns-server) forwarding requests to DNS server (config system dns). The latter has a setting "cache-notfound-responses".

I was hoping that by enabling that setting and issuing "diagnose test application dnsproxy 13" (to show DNS cache) I'd be able to see which requests failed resolution, but that command does not seem show this.

Is there another method to see failed resolve requests?

R's, Alex