The overall structure of an inverse query for retrieving the domain name that corresponds to Internet address 10.1.0.52 is shown below:
|Answer||<anyname> A IN 10.1.0.52|
This query asks for a question whose answer is the Internet style address 10.1.0.52. Since the owner name is not known, any domain name can be used as a placeholder (and is ignored). A single octet of zero, signifying the root, is usually used because it minimizes the length of the message. The TTL of the RR is not significant. The response to this query might be:
|Question||QTYPE=A, QCLASS=IN, QNAME=VENERA.ISI.EDU|
|Answer||VENERA.ISI.EDU A IN 10.1.0.52|
Note that the QTYPE in a response to an inverse query is the same as the TYPE field in the answer section of the inverse query. Responses to inverse queries may contain multiple questions when the inverse is not unique. If the question section in the response is not empty, then the RR in the answer section is modified to correspond to be an exact copy of an RR at the first QNAME.