About
A DNS lookup is a request to a DNS server in order to get DNS record from a DNS name
- a AAAA query will get you the ipv6 address
- a TXT query will get your a TXT record
- …
Beware that not all DNS clients are performing a lookup on the content of the host file as ping does.
Example of response known as replies
Each message 1) consists of:
- a header with:
- ID: query identifier
- QR: message type:
- 0: query
- 1: response
- OPCODE: kind of query:
- 0: standard query (QUERY)
- 2: a server status request (STATUS)
- RCODE: Response code:
- 0: No error
- 1: Query Format error
- 2: Server failure
- 3: Name Error (the domain name referenced in the query does not exist)
- 4: Query Type Not Implemented
- 5: Refused (For Policy reason)
- and four sections:
- question: the question for the name server composed of:
- a query type (QTYPE),
- a query class (QCLASS),
- a query domain name (QNAME).
- answer: the answer (in resource records (RR) format),
- with a status code 2)
- authority: the authoritative name server (in RR format),
- and an additional space information (in RR format)
A header field (flags) controls the content of these four sections
Example of A record query against datacadamia.com
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 56993
;; flags: qr rd ra ; qd: 1 an: 2 au: 0 ad: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0; flags: ; udp: 512
;; QUESTIONS:
;; datacadamia.com., type = A, class = IN
;; ANSWERS:
datacadamia.com. 300 IN A 188.114.96.0
datacadamia.com. 300 IN A 188.114.97.0
;; AUTHORITY RECORDS:
;; ADDITIONAL RECORDS:
;; Message size: 76 bytes
Type
Forward
A forward lookup translate a DNS name to an IP. See What is a DNS Forward Lookup?
Reverse
A reverse lookup translate a an IP to a DNS name. See DNS - rDNS - Reverse DNS (lookup|resolution) - from IP to name