The following table explains the DNS return codes that can be returned when doing a DNS query and may appear in your logs. Each return code has its own purpose in the DNS infrastructure. Typically, you'll see NOERROR (RCODE:0) when doing most of your successful browsing, all of the other return codes are consider errors.
For an exhaustive list of these codes, please see the DNS RCODEs section of this link: http://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml
DNS Return Message
DNS Response Code
DNS Query completed successfully
DNS Query Format Error
Server failed to complete the DNS request
Domain name does not exist.
Function not implemented
The server refused to answer for the query
Name that should not exist, does exist
RRset that should not exist, does exist
Server not authoritative for the zone
Name not in zone