DNS: The Hacker's Phone Book

When you want to visit LinkedIn or check out the latest news, there’s something happening behind the scenes that makes this whole experience a breeze: DNS, or the Domain Name System.

DNS is like the Internet's phone book, translating easy-to-remember names (like linkedin.com) into IP addresses (like 142.250.190.206), so you don’t have to remember long strings of numbers just to check your messages. Let’s dive into how DNS works and explore the different types of records it maintains.

How Does DNS Work?

Picture this: you type a website name into your browser. Your computer’s Stub Resolver (a small program that helps find IP addresses) first checks if it already knows the IP address by looking in its cache. If you’ve been to that website recently, it’s stored there, easy-peasy, no extra work needed!

But, if it’s your first time visiting that site or your cache has cleared, things get a bit more interesting. The Stub Resolver needs a helping hand, so it reaches out to a Recursive DNS Server, the internet’s “information hub”, to look up the IP address. Some popular Recursive DNS Servers include:

• Google’s DNS: 8.8.8.8 and 8.8.4.4
• Cloudflare’s DNS: 1.1.1.1 and 1.0.0.1
• OpenDNS (Cisco): 208.67.222.222 and 208.67.220.220
• Quad9: 9.9.9.9 and 149.112.112.112

Let’s imagine your Resolver asks Google’s DNS (8.8.8.8) for LinkedIn’s IP address. If Google’s DNS has seen LinkedIn recently, it’ll pass back the IP address. If not, Google DNS gets to work, by asking other servers.

Meeting the DNS "Mafia" (Root Servers)

Google’s DNS reaches out to one of the 13 Root Servers (think of them as the Godfathers of the DNS world). These servers don’t store IP addresses for specific websites but instead point to the servers that handle Top-Level Domains (TLDs) like .com, .net, or .org. They send Google DNS along to the next stop: the TLD Servers.

Going Down the Rabbit Hole: TLD and Authoritative DNS Servers

The TLD Servers (for example, those managing .com domains) now come into play, and they know exactly where to find LinkedIn.com’s IP address, by asking Authoritative DNS Servers. Authoritative DNS Servers store the actual records that link LinkedIn’s domain name to its IP address.

Once the Authoritative DNS Server finds LinkedIn’s IP address, it relays this information back to Google DNS, which then stores it in its cache and finally sends it back to your device. You’re now connected to LinkedIn without typing a single IP address!

Types of DNS Records

Each domain has a “zone file” that holds different types of DNS records, each serving a specific purpose:

1. A Record The A Record links domain names to IPv4 addresses, so when you type linkedin.com, it can be resolved to an IP address. It also includes a TTL (Time to Live), which tells the DNS how long to hold onto this info before updating.
2. NS (Name Server) Record This record points to the Authoritative DNS Server responsible for managing a domain. When the Recursive Server reaches a TLD Server, the NS Record guides it to the right DNS server for that specific domain.
3. AAAA Record Just like the A Record but for IPv6 addresses. It’s the future-proof cousin of the A Record, handling longer addresses (think beyond 192.168.1.1).
4. MX (Mail Exchange) Record This one tells your email client where to send emails for a domain. For instance, if you’re sending an email to [email protected], the MX record guides it to LinkedIn’s mail server.
5. PTR (Pointer) Record A reverse lookup record, it lets you map an IP address back to a domain name. PTR Records are often used for security, especially to reduce spam.
6. CNAME (Canonical Name) Record This is an alias used to redirect subdomains to the main domain. For instance, www.example.com might redirect to example.com. It’s like setting up a “nickname” that points back to the main name.
7. TXT Record TXT Records are for holding plain text, often used to verify domain ownership or set up email security protocols. Admins can leave notes or configure security settings here.
8. SOA (Start of Authority) Record Every DNS zone has an SOA Record that holds details like the primary name server, admin contact email, and the current serial number (indicating version). It’s like the official documentation for a zone, ensuring DNS zones are managed correctly.
9. SRV (Service) Record Points to specific services within a domain, directing queries to particular ports. For instance, an SRV Record can tell a client where to find a specific service like FTP or SIP.

Understanding CNAMEs and Domain Structure

When a computer reads www.example.com, it’s actually reading it from right to left! Here’s the breakdown:

1. Root Domain: The dot at the end (hidden in most browsers) represents the Root Domain.
2. Top-Level Domain (TLD): The .com portion tells DNS servers to look for sites within the “.com” realm.
3. Second-Level Domain (SLD): “example” identifies the website itself.
4. Subdomain: You might see “www.” or “ftp.” as a subdomain, redirecting users to specific parts of a site.

Imagine you’re managing a website with multiple services, and you create a subdomain, like ftp.example.com. If you want ftp.example.com to point to example.com, you’d use a CNAME Record to make sure users land in the right place!

Ready for a DNS Adventure?

DNS may sound complicated, but it’s the unsung hero that makes the Internet run smoothly. Without it, we’d be memorizing endless strings of numbers just to visit our favorite sites.