Introduction to DNS

Introduction to DNS: The Foundation of Modern Internet

Due to the proliferation of the internet, browsing to websites from our computers, phones, and tablets is now an integral part of our daily lives. The entire experience of surfing the web involves navigating to user-friendly domain names that are easy for us humans to remember.

For online shopping, we browse sites like www.amazon.com or www.ebay.com. For online banking, we navigate to websites such as www.americanexpress.com, and to watch the latest movies, we visit sites like www.netflix.com. For news and information, we turn to www.bbc.co.uk or similar trusted sources.

What is DNS?

The problem is, however, that unlike humans, computers work with numbers. Each device connected to the internet has a unique IP address which other machines use to find it. While we can browse websites by typing their IP addresses into our browser, we cannot easily remember and use complex numerical addresses for our daily internet activities.

This is where DNS comes in. DNS stands for Domain Name System, and it is the underlying protocol that acts as the intermediary, allowing for the translation of human-friendly domain names such as www.bbc.co.uk to the IP addresses that belong to the computer systems hosting the actual content we want to access.

The Domain Name System (DNS) is often referred to as the phonebook of the Internet. Just like a conventional phonebook where we perform a lookup against a name to get its associated phone number, DNS works by translating domain names (like rjscloudacademy.com or linkedin.com) into the numerical IP addresses that web browsers need to load Internet resources.

Every single device on the Internet has a unique IP address by which it can be uniquely identified by other online devices. A DNS server eliminates the need for us to memorize these IP addresses every time we want to visit a site or connect to a device.

Without DNS, we would need to know and type the exact IP address of every site we wish to visit, such as:

• IPv4 addresses: Like 192.168.1.1 or 51.23.8.9
• IPv6 addresses: More complex alphanumeric addresses such as 2400:CB00:2048:1::C629:D7A2

Needless to say, this is not practical at all, even for technical individuals. DNS has been created with the aim of eliminating the need for humans to memorize IP addresses and instead allows us to use human-friendly domain names while browsing.

Key Insight: In summary, without DNS, we would not be able to use the internet as we do today. DNS makes the crucial link between typing a domain name into a browser and reaching the computer system that hosts the desired content.

• DNS is a directory service that provides a mapping between the name of a host on the network and its numerical address.
• The core function of DNS is to map symbolic names to IP Addresses.

Three main functions of DNS:

• Name Space: Namespace defines how domain names are structured and used - what makes a name valid, what format it should have, what characters and symbols are allowed, and how names are interpreted.
• Name Resolution: This function is the process of translating domain names to IP addresses, which is the most commonly understood DNS operation.
• Name Registration: This covers how domains are registered, how their uniqueness is guaranteed, and identifies the registration authorities responsible for the name assignment process.

The DNS architecture consists of a hierarchical and decentralized name resolution system for computers, services, and any other resources connected to the Internet or a private network. It stores various associated information for the domain names assigned to each resource.

Queries for a resource pass through the DNS system with URLs as parameters. The DNS then translates these URLs into target IP addresses and sends the queries toward the correct resources.

How does DNS work?

The first thing we need to understand is that there isn't a single DNS server, but rather a hierarchical system of interconnected DNS servers that work together to resolve domain names to IP addresses.

Think of DNS resolution as a journey through multiple checkpoints, each with specific knowledge and responsibilities. A computer has its own cache of DNS data – a local IP-address-to-URL matching – that it uses for quick references. However, it cannot store information for every website on the internet, which is why we need root servers, recursive servers, Top Level Domain (TLD) servers, and authoritative DNS servers.

The DNS Resolution Process:

When you type a domain name (like www.amazon.com) into your browser, the following step-by-step process occurs:

• Step 1 - Local Cache Check: The browser first checks the local DNS cache for the correct resolution (from URL to IP address). If found, the process stops here for maximum speed.
• Step 2 - Recursive DNS Server: If not found locally, the query goes to the recursive DNS server – which is normally operated by your local ISP provider – to check which root DNS server it needs to contact to find an answer.
• Step 3 - Root DNS Servers: The query reaches one of the root DNS servers (run by about 13 independent organizations worldwide) to find the address of the correct Top-Level Domain (TLD) server. The root servers determine whether to query ".com", ".org", ".net", or other TLD servers. Important note: Every website address has an implied "." at the end (even though we don't type it), which designates the DNS root nameservers at the top of the hierarchy.
• Step 4 - TLD Servers: At the TLD server (there are about 1,000 TLD servers spread across the globe), the query is directed toward the correct authoritative DNS server where the actual IP address information is stored.
• Step 5 - Authoritative DNS Server: Finally, at the authoritative DNS server – which holds the definitive IP address information for the domain – the corresponding IP address is sent back through the chain: authoritative DNS → TLD → root → recursive DNS → your computer. Now your browser can connect to the website.

DNS Caching and Performance

Every time a DNS query is resolved, the IP address to URL mapping is cached at multiple levels (your computer, recursive DNS, etc.) for the next user, instead of having to repeat the entire lookup process. This caching mechanism:

• Keeps DNS servers synchronized and updated
• Results in significantly faster response times for subsequent requests
• Reduces load on the global DNS infrastructure
• Improves overall internet browsing experience

DNS Complexity: While DNS can be compared to a phonebook for simplicity, it is actually far more sophisticated. Its versatility extends well beyond translating domain names to IP addresses, and its depth and complexity become more apparent as you delve deeper into network engineering.

Why DNS Matters

Understanding DNS is crucial for network engineers and IT professionals because:

• Foundation Protocol: DNS is one of the most important internet protocols, enabling virtually all internet communication
• Performance Impact: DNS resolution speed directly affects user experience and application performance
• Security Implications: DNS can be leveraged for security (DNS filtering) or exploited by attackers (DNS poisoning)
• Troubleshooting: Many network connectivity issues stem from DNS problems
• Modern Applications: Cloud services, CDNs, and modern web applications heavily rely on sophisticated DNS configurations

This introduction provides the foundation for understanding DNS architecture, operations, and troubleshooting – essential knowledge for anyone working with modern network infrastructure.