What are DNS? - Complete Guide
The Domain Name System (DNS) is a fundamental Internet infrastructure that acts as a digital "phone book". Its main function is to translate domain names that we easily remember (like google.com) into the numerical IP addresses that computers need to communicate with each other.
Complete Technical Definition
DNS is a hierarchical decentralized naming system for devices connected to IP networks like the Internet or a private network. This system associates various information with domain names assigned to each of the participants connected to the network.
The DNS server uses a distributed and hierarchical database that stores information associated with domain names on networks like the Internet. Although as a database DNS is capable of associating different types of information to each name, the most common uses are:
- Mapping domain names to IP addresses (A and AAAA records)
- Locating email servers (MX records)
- Authenticity verification (TXT records for SPF, DKIM)
- Service addressing (SRV records)
- Domain aliases (CNAME records)
How Do DNS Work? - Detailed Process
When you type a URL in your browser, a complex DNS resolution process occurs involving multiple levels:
1
Local Query (DNS Cache)
Your device first checks its local DNS cache to see if it already knows the IP of the requested domain. If found and not expired, it's used immediately.
2
Recursive DNS Server
If not in cache, the query is sent to the recursive DNS server (configured on your device). This server acts as an intermediary and has its own cache.
3
Root Servers Query
If the recursive server doesn't know the answer, it queries the 13 global Root Server clusters that know the location of top-level domain servers (.com, .org, etc.).
4
TLD Servers
Root Servers redirect the query to appropriate Top Level Domain (TLD) servers (.com, .es, .org), which know the authoritative servers for each domain.
5
Authoritative Server
Finally, the specific domain's authoritative DNS server is queried, which contains definitive information and returns the actual IP address.
6
Response and Cache
The response is sent back through the entire chain, each server caches the information according to the configured TTL (Time To Live) for future queries.
Main DNS System Components
๐ฅ๏ธ DNS Clients (Resolvers)
Client programs that run on user devices and generate DNS name resolution requests to DNS servers. Include operating system libraries and applications like web browsers.
๐ Recursive DNS Servers
Servers that accept client queries and do the work of resolving names by querying other DNS servers if necessary. They maintain caches to improve performance.
๐๏ธ Authoritative DNS Servers
Servers that have authority over specific zones of the DNS namespace and provide definitive answers for domains under their control.
๐
Authority Zones
Parts of the domain namespace over which a DNS server has authority. Each zone contains DNS records that define information associated with domains in that zone.
Main DNS Record Types
| Type |
Function |
Example |
| A |
Maps a name to an IPv4 address |
example.com โ 192.168.1.1 |
| AAAA |
Maps a name to an IPv6 address |
example.com โ 2001:db8::1 |
| CNAME |
Alias from one name to another |
www.example.com โ example.com |
| MX |
Specifies mail servers |
example.com โ mail.example.com |
| TXT |
Arbitrary text information |
SPF, DKIM, verifications |
| NS |
Specifies authoritative name servers |
example.com โ ns1.provider.com |
โ Back to top
Complete History of the DNS System
The Early Days: The HOSTS File
In the early days of the Internet (then ARPANET), name resolution was performed using a centralized file called HOSTS that contained all known host names and their corresponding IP addresses. This file was maintained by SRI International (formerly Stanford Research Institute) and distributed manually to all computers connected to the network.
The system worked similar to a physical phone book: each computer had a local copy of the file that it consulted to resolve names. However, the explosive growth of ARPANET made this centralized system impractical for several reasons:
- The file grew constantly and was difficult to keep updated
- Name conflicts were common
- Manual distribution was slow and inefficient
- There was no scalability for future growth
The Birth of Modern DNS (1983-1987)
Recognizing the limitations of the HOSTS system, Jon Postel began working on a more scalable solution. In November 1983, Postel published RFC 881 that outlined the basic concepts of what would become DNS.
Subsequently, Paul Mockapetris, working at the University of Southern California, developed with Postel the foundational DNS documents:
๐
RFC 882 and RFC 883 (1983)
These documents defined the basic DNS architecture, including the concept of hierarchical namespace and database distribution.
๐
RFC 920 (October 1984)
After extensive discussions and refinements, this RFC was published defining the requirements for domain registration in the new system.
๐๏ธ
RFC 1034 and RFC 1035 (1987)
These documents replaced the previous RFCs and established the definitive DNS specifications that still form the basis of the current system.
The Master-Slave Replication Era
In early DNS implementations, a master-slave replication model was adopted to provide redundancy and availability:
- Master Server: Contained the authoritative copy of zone data
- Slave Servers: Maintained copies of data and periodically queried the master
- Zone Transfers: Slaves synchronized their data through complete transfers
- Periodic Verification: Slaves regularly checked if data had changed
Evolution and Improvements (1995-2000)
Approximately 10 years after initial implementation, significant improvements were made to the DNS protocol to make it more efficient and dynamic:
๐
NOTIFY (RFC 1996)
Revolutionized synchronization by allowing the master server to actively notify slaves about changes, eliminating the need for constant periodic queries.
๐
IXFR - Incremental Transfers (RFC 1995)
Allowed only changed records to be transferred, instead of transferring the entire zone, significantly improving network efficiency.
๐
Dynamic DNS - DDNS (RFC 2136)
Introduced the ability to update DNS records automatically, allowing administrators to make changes without manually editing zone files.
๐ง
EDNS - Extension Mechanisms (RFC 2671)
Modernized the DNS protocol allowing larger messages and new functionalities, paving the way for future extensions.
The Internationalization Era (2003-2010)
With the global expansion of the Internet, the need arose to support non-ASCII characters in domain names:
๐
IDN - Internationalized Domain Names
RFC 5890 and RFC 5891 (2010) defined how to include characters from other languages in domain names, allowing domains in Arabic, Chinese, Cyrillic and other alphabets.
๐
DNSSEC - Security Extensions
DNS security extensions were developed to provide authentication and integrity of DNS data, protecting against cache poisoning attacks.
Root Servers: The Heart of DNS
The Root Servers are the foundation of the entire global DNS system. There are 13 root server clusters (labeled A through M) distributed globally that maintain information about all top-level domains (TLD) like .com, .org, .es, etc.
These servers are operated by different organizations and are critical to the functioning of the Internet. The security of these servers is maintained through DNSSEC and highly secure key signing ceremonies.
To learn more about the root server security process, you can consult detailed information about the DNSSEC root zone key signing ceremony.
DNS in the Modern Era (2010-2025)
โ๏ธ
Cloud DNS
Major providers like Google, Cloudflare, and Amazon have launched public DNS services with massive global infrastructure and advanced security features.
๐
DNS over HTTPS (DoH) and DNS over TLS (DoT)
New protocols that encrypt DNS queries to improve user privacy and security.
๐ค
Smart DNS
Modern implementations include geographic load balancing, service health detection, and adaptive responses based on user location.
๐ก๏ธ
DNS Filtering and Security
Modern DNS services include malware filtering, ad blocking, and parental controls integrated directly into DNS resolution.
โ Back to top