The DNS

You've learned about IP addresses - the numerical identifiers that allow devices to communicate on the internet. But you don't usually type IP addresses into your browser, do you? You use domain names like google.com or wikipedia.org. So, how does your computer translate those easy-to-remember names into the numerical IP addresses it needs? That's where DNS (Domain Name System) comes in - it's the internet's phone book.

What is DNS?

DNS is a hierarchical and distributed system that translates human-readable domain names (like www.example.com) into the numerical IP addresses (like 192.168.1.1) that computers use to identify each other on the internet. It's like a giant, global directory service.

Without DNS, you'd have to remember and type in the IP address of every website you wanted to visit. Imagine trying to remember 172.217.160.142 instead of google.com! DNS makes the internet much more user-friendly.

How DNS Works: The Lookup Process

When you type a domain name into your browser, here's a simplified overview of what happens behind the scenes:

1. The Request: Your browser (the client) needs to find the IP address associated with the domain name. It starts by asking a DNS resolver. Often, your internet service provider (ISP) provides a DNS resolver, but you can also use public resolvers like Google Public DNS or Cloudflare DNS.
2. Recursive Query: The DNS resolver doesn't usually know the IP address offhand. It starts a recursive query, meaning it will ask other DNS servers until it finds the answer.
3. Root Servers: The resolver first contacts one of the root name servers. There are 13 sets of root servers around the world, and they are the top of the DNS hierarchy. They don't know the IP address of example.com, but they know which servers are responsible for the .com top-level domain (TLD).
4. TLD Servers: The root server directs the resolver to a TLD (Top-Level Domain) name server. TLD servers are responsible for specific domain extensions like .com, .org, .net, .edu, etc. The TLD server for .com doesn't know the IP address of www.example.com, but it knows which servers are responsible for the example.com domain.
5. Authoritative Name Servers: The TLD server directs the resolver to an authoritative name server for the specific domain (example.com in our example). These servers are maintained by the domain name registrar (the company where the domain name was registered) or the website owner. The authoritative name server does know the IP address associated with www.example.com.
6. The Answer: The authoritative name server sends the IP address back to the DNS resolver.
7. Caching: The DNS resolver caches (stores) the IP address for a certain period (determined by the "Time to Live" or TTL value). This speeds up future lookups for the same domain name.
8. Response to Client: The DNS resolver sends the IP address to your browser.
9. Connection: Your browser now has the IP address and can connect directly to the web server hosting www.example.com to request the web page.

This entire process, involving multiple DNS servers, usually happens in milliseconds.

The DNS Hierarchy

DNS is organized in a hierarchical structure, like an upside-down tree:

• Root: At the top are the root name servers.
• Top-Level Domains (TLDs): Below the root are TLDs, such as .com, .org, .net, .edu, .gov, and country-code TLDs like .uk, .ca, .jp.
• Second-Level Domains: These are the domains that you register, like example in example.com.
• Subdomains: These are further divisions within a domain, like www in www.example.com or blog in blog.example.com.

This hierarchical structure allows DNS to be distributed and managed efficiently. No single server needs to know all the IP addresses for every domain name on the internet.

DNS Records

DNS servers store information about domain names in DNS records. There are many different types of DNS records, each serving a specific purpose. Some of the most common include:

• A Record (Address Record): Maps a domain name to an IPv4 address. This is the most common type of record, used for finding the IP address of a website.
• AAAA Record (IPv6 Address Record): Maps a domain name to an IPv6 address.
• CNAME Record (Canonical Name Record): Creates an alias for a domain name. For example, www.example.com might be a CNAME record pointing to example.com.
• MX Record (Mail Exchange Record): Specifies the mail servers responsible for receiving email messages for a domain.
• TXT Record (Text Record): Stores text-based information about a domain. Often used for verification purposes or for storing additional data.
• NS Record (Name Server Record): Specifies the authoritative name servers for a domain.