DNS, which stands for Domain Name System, is a distributed database system that converts domain names into IP addresses. At its heart, DNS solves a simple but crucial problem: humans prefer memorable names, while computers need numbers. Without DNS, you’d need to memorize strings of numbers like 192.168.1.1 instead of simple website names.
The system works like a massive, distributed directory that’s constantly updating and evolving.DNS creates a bridge between human language and machine language. Every time you click a link or type a URL, DNS servers worldwide spring into action, working together to get you to your destination. This process happens so quickly that most users don’t notice it’s occurring.
Key Concepts
- DNS translates domain names (e.g., www.example.com) into IP addresses (e.g., 192.0.2.1)
- It operates as a distributed database implemented across a hierarchy of DNS servers
- DNS functions as an application layer protocol enabling hosts to query this distributed database
The Need for DNS
Imagine trying to remember the IP address for every website you visit. It would be like memorizing phone numbers for every person you know instead of using their names in your contact list. DNS solves this problem by allowing us to use easily remembered domain names while computers handle the complex IP addresses behind the scenes.
How DNS Works
The DNS resolution process involves several steps and components.
When you type a website address into your browser, you begin a fascinating journey through the internet’s addressing system. DNS acts as a translator, converting human-readable website names into computer-friendly IP addresses and vice versa.
Phase 1 - Local Memory Check
The process starts with checking the device’s local DNS cache. This first step queries temporarily stored DNS records in memory, significantly reducing response time and network traffic for recently accessed domains.
Phase 2 - The Local Guide (DNS Resolver)
If the address is not found in the local cache, the query is forwarded to a DNS resolver. This specialized server maintains an extensive cache of DNS records and is configured to perform recursive queries on behalf of clients. The resolver checks its own cache before initiating a complete query through the DNS hierarchy.
Phase 3 - The Global Directory (Root Servers)
When the resolver needs assistance, it contacts one of the 13 unique root server names (A to M) distributed worldwide. Each name corresponds to a shared IP address, supported by multiple anycast instances. These servers are strategically positioned to ensure global availability and low latency.
Today, it is also possible to configure a DNS resolver to operate with a local copy of the root zone, as described in RFC 8806. This eliminates the need to query external root servers directly, improving efficiency and privacy.
Phase 4 - The Specialized Directories (TLD Servers)
The root servers direct the query to TLD (Top-Level Domain) servers. These are like specialized departments that handle specific types of addresses. For example One department handles all .com addresses Another manages .org addresses A different one takes care of .net addresses
Phase 5 - The Final Answer (Authoritative Server)
The last stop is the authoritative server, which is like the ultimate expert for the specific website you’re looking for. This server knows everything about the domain, including its exact IP address.
Phase 6 - The Return Journey
Once the authoritative server provides the address, the information travels back through the same path Authoritative server → TLD server TLD server → Root server Root server → DNS resolver DNS resolver → Your device
Remember: This entire journey typically happens in milliseconds, making your internet browsing experience smooth and seamless.
This systematic approach to DNS resolution ensures that billions of internet users can reliably access websites worldwide, making it one of the most crucial systems in modern internet infrastructure.
DNS System Architecture
The DNS system is structured hierarchically
- Root Servers: 13 sets of root servers globally distributed
- Top-Level Domain (TLD) Servers: Manage domains like .com, .org, .net
- Authoritative Name Servers: Store and provide the actual IP addresses for specific domains
In short, this is a basic example of how DNS works
- The client asks the local server for name resolution (for example, www.azion.com.br);
- The local server asks www.azion.com.br to a root server;
- The root server responds: who is responsible for .br is 2xx.2xx.1xx.10;
- The local server asks the server responsible for .com.br for www.azion.com.br;
- The server responsible for .com.br responds: who is responsible for .com.br is this one 179.191.xxx.2;
- The local server asks www.azion.com.br to the authoritative server responsible for azion.com.br;
- The authoritative server responsible for azion.com.br responds to the local server www.azion.com.br = 2xx.2xx.2xx.4;
- The local server sends the response www.azion.com.br = 2xx.2xx.2xx.4 to the user.
The following image shows the architecture and the flow of the DNS system mentioned earlier
This hierarchical structure allows for efficient management and distribution of domain information across the internet.
Important DNS Components
IP Addresses
IP addresses are unique numerical identifiers for devices connected to the internet. DNS links these addresses to human-readable domain names, facilitating easier internet navigation.
Domain Name Space
The Domain Name Space, also known as the domain hierarchy, has a hierarchical structure in an inverted tree format, and contains specifications of domain names and data associated with those names. This name space is divided into domains, and the responsibility for managing names within each domain is delegated to systems within each domain. That is, the naming structure is divided into small, manageable zones. Each DNS server maintains a specific database file and is only responsible for managing the name-to-IP mappings for that small part of the DNS structure. When a DNS server receives a request for name translation that is not part of the DNS zone, the DNS server forwards the request to another DNS server in the appropriate zone for translation.
Check the domain hierarchy in the following image
About this structure:
- each intersection (in this case, the rectangle with a name inside) is called a node;
- each node represents a domain;
- each domain has a name, so each node in this structure is called a domain name;
- the domain name identifies each one’s position in the DNS logical hierarchy relative to its primary domain. Each domain name consists of a few names separated by dots;
- each domain can contain subdomains;
- a subdomain is part of a larger domain. For example, documentation.azion.com and blog.azion.com are subdomains of the azion.com domain;
- domains and subdomains are grouped into zones to allow for distributed administration of the namespace.
DNS Servers
DNS (Domain Name System) servers play a crucial role in the functioning of the internet. They act as the internet’s phonebook, translating human-readable domain names into IP addresses that computers use to identify each other. Let’s explore the key aspects of DNS servers:
Core Functions of DNS Servers
DNS servers perform three essential tasks:
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External Query Resolution: They respond to queries from external clients or servers on the internet about names registered in their local domain.
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Local Name Resolution: DNS servers perform internet domain name resolutions for their local customers (machines within their domain).
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Caching: To expedite future queries, these servers cache the name resolutions requested by their clients in a local cache.
Types of DNS Servers
Based on their functionality, DNS servers can be classified into three main categories:
Primary (Master) Servers
- Responsible for a specific domain.
- Handle the addition, alteration, or deletion of records for that domain.
- Serve as the authoritative source for domain information.
Secondary (Slave) Servers
- Function as backups to the primary server.
- Receive domain records from the primary server through a process called zone transfer.
- Respond to customer requests when needed.
- Enhance reliability and load distribution.
Caching-only Servers
- Focus solely on querying and returning results.
- Maintain a local cache of recent queries.
- Not responsible for any specific domain.
- Primary function is to improve the performance of name resolutions for local clients by utilizing their cache.
The Importance of DNS Server Types
Understanding these different types of DNS servers is crucial for:
- Network Administration: Proper setup and management of DNS infrastructure.
- Performance Optimization: Utilizing caching servers to reduce network load and speed up resolutions.
- Reliability: Implementing secondary servers for redundancy and load balancing.
- Security: Maintaining control over domain information with primary servers.
By leveraging the strengths of each type of DNS server, it’s possible to create a robust, efficient, and reliable DNS infrastructure that forms the backbone of internet communication.
Security and Reliability
Modern DNS incorporates dynamic answers and various security measures to protect users. DNSSEC, for example, adds digital signatures to DNS records, ensuring you reach legitimate websites rather than fraudulent copies. This security layer acts like a virtual bouncer, checking IDs before letting anyone through.