DNS (Domain Name System)
The Domain Name System (DNS) describes both a protocol and the infrastructure that maps domain names to IP addresses.
In this system, a DNS client issues DNS requests (or DNS address lookups) by sending a domain name to a nameserver (or DNS server).
DNS Hierarchy
At the root of its hierarchy, the Domain Name System only has 13 named servers for IPv4.
DNS Message Format
The two types of DNS messages are query and response.
Header section (12 Bytes):
- 7 bit flag field containing..
- AA: Authoritative Answer
- TC: Truncated Response
- RD: Recursion Desired
- RA: Recursion Available
- Reserved
- AD: Authentic Data (Reserved)
- CD: Checking Disabled (Reserved)
Question section:
- …
Answer section:
- …