Firescope agent network_dns_availability operation

I am interested in what mechanism is used by the Firescope Agent for network_dns_availability operation.  

Does the Firescope Agent network_dns_availability use nslookup?  What records is the operation trying to query - is it A records, MX, or what?

Currently I have set up several attributes set up for network_dns_availability and some are showing failed that do show up through nslookup while others report correctly.  With these types of false positives I do not have confidence in using this operation to accurately monitor DNS availability.