Forward-confirmed reverse DNS

Forward -confirmed reverse DNS ( FcrDNS ) or, more specifically forward -confirmed reverse DNS lookup called two consecutively executed DNS queries where initially to an IP address, the associated name is determined (so-called reverse DNS lookup ), and then to that name associated IP address.

Where the result of the second query back to the original IP address, so this is considered to be forward confirmed ( reconfirmed ).

Importance

A successful FcrDNS exam is an indication of a connection between the owner of a domain, and the owner of that CIDR address block, which originates from the IP address.

She is also an indication that both owners have at least a basic understanding of the relevant RFCs and are able to configure their servers properly.

Application

A negative result may indicate poorly maintained server or a zombie PC. A mail server for example can use this feature to block spam.