What is DNS? – How the Domain Name System Works

The Domain Name System (DNS) is the phone book of the internet. It translates domain names that humans can easily remember (like example.com) into IP addresses (like 192.0.2.1) that computers use to identify each other on a network. Understanding DNS is crucial for anyone managing a website or server.

In this comprehensive beginner’s guide, I’ll cover:

• What is DNS and why is it needed?
• How does DNS work? The 10 step DNS lookup process
• Types of DNS servers – recursive, authoritative, root
• DNS record types – A, CNAME, MX explained
• How to troubleshoot common DNS problems
• DNS security threats and how to prevent them
• Public DNS services from Cloudflare, Google, etc

Let’s get started…

What is DNS and Why Do We Need It?

The Domain Name System (DNS) is like an address book for websites. It translates human-readable domain names into IP addresses that computers can use to connect to each other on the internet.

Some key reasons we need DNS:

• Humans can’t remember numbers easily. IP addresses like 192.168.1.1 are hard to remember. Domain names like example.com are much easier.
• IP addresses change sometimes. DNS allows the domain name to stay the same even if the IP address changes.
• Managing many devices is easier with names. Give each device a domain name rather than tracking many IP addresses.

Without DNS, using websites, email, ftp, and most internet services would be extremely difficult. DNS makes the internet usable.

How Does DNS Work? The 10 Step DNS Lookup Process

When you type a web address like example.com into your browser, a lot happens behind the scenes to translate that domain name into an IP address so your computer can load the website.

Here are the 10 key steps in a typical DNS lookup process:

1. Browser cache – Your browser checks its local cache for a prior DNS lookup for the requested domain. If found, it uses that IP address to load the site.

2. Operating system cache – If not in the browser cache, it checks the OS-level cache next for a saved DNS record.

3. Router cache – Your router maintains a DNS cache as well. If no match there, the router sends the DNS query to your ISP’s DNS recursors.

4. ISP recursive DNS servers – Your ISP maintains a pool of recursive DNS servers which will attempt to fully resolve the DNS query. It first checks its own cache.

5. Root nameserver query – If not cached, the recursive resolver queries a DNS root nameserver (there are 13 total) to find which TLD nameserver to ask next.

6. TLD nameserver query – The TLD (top-level domain) nameserver returns details for the next authoritative nameserver to ask.

7. Authoritative nameserver – The authoritative nameserver for example.com will have the actual DNS records needed to resolve the domain name, usually an A record with IP address.

8. ISP recursive DNS returns record – The recursive resolver caches the response and returns the final IP address record to your router’s DNS request.

9. Router caches and returns IP to computer – Your router caches the response too and sends the real IP address for the domain back to your computer.

10. Website loads – With the IP address now in hand, your web browser can load the real website, usually hosted on a web server somewhere globally.

That seems like a lot of back and forth! Good thing it happens instantly for the user. DNS makes finding websites easy by handling all that translation behind the scenes quickly and reliably.

Let’s take a deeper look at the different types of DNS servers that make this process possible…

Types of DNS Servers and Their Roles

There are three main types of DNS servers that each play an important role:

• Recursive resolvers
• Authoritative nameservers
• Root servers

Understanding the difference helps troubleshoot DNS issues faster:

1. Recursive DNS Servers

Recursive resolvers do most of the repetitive lookups needed to fully resolve a DNS query. This includes contacting all the other DNS servers like root servers, TLDs, and authoritative nameservers until it gets a final IP address record.

Your ISP provides recursive DNS to customers. Large companies also maintain their own internal recursive servers. Public third parties like Google Public DNS and Cloudflare also offer public recursive DNS.

2. Authoritative Nameservers

Authoritative nameservers are the source of truth for a domain’s DNS records. Domain registrars maintain these nameservers on behalf of customers. When a site owner updates DNS records for their domain, those changes propagate out to the authoritative nameservers assigned to that domain.

These servers answer DNS queries directly with a DNS response instead of doing more lookups. Their configuration comes from the DNS zone files maintained for that domain.

3. Root DNS Servers

The 13 DNS root servers form the backbone the internet for DNS resolution. These servers maintain pointers to all TLD (top-level domains) like .com, .net, and country-codes like .uk, .in etc.

All DNS queries eventually query a root server to find which TLD nameserver to ask for more details about the final authoritative nameserver needed.

Without root servers, DNS wouldn’t function at all! ICANN maintains these critical master servers globally with built-in redundancy and automatic load balancing.

Recursive Vs. Authoritative DNS: Key Differences

Recursive resolvers answer DNS queries on behalf of clients, handling all the follow-up lookups needed across different nameservers to find the final domain -> IP address answer.

Authoritative nameservers are purely a source of DNS answers for domains under their management. They reply with direct DNS answers for those domains only, without doing any further lookups downstream.

A typical DNS lookup query will touch both kinds of servers in sequence to fully resolve a domain name all the way to an IP address.

DNS Record Types Explained

We’ve covered the various DNS server types. Now let’s look at some common DNS record types they use to store domain information:

• A record – Maps a domain name to IPv4 address. Most common and required record type.
• AAAA – Maps a domain name to IPv6 address. Used for websites accessible via IPv6.
• CNAME – Creates an alias from one domain name to another. Allows sharing one IP.
• MX – Defines mail servers for a domain name (used for email routing)

There are many advanced record types we won’t cover here also used for geo-routing, load balancing, and other functions.

A registrar’s DNS control panel allows managing these DNS records to control how your domain name resolves globally. For example, an A record ties your domain to a web-server’s IP for hosting websites and web apps.

Now that we understand the basics, let’s cover some common DNS issues people run into…

How to Troubleshoot Common DNS Problems

Small DNS problems can completely break access to your website or other internet services. Some ways to identify and fix them:

• Flush the DNS cache on your computer to refresh records, especially after making DNS changes. The ipconfig /flushdns command does this in Windows.
• Confirm your domain is using the correct nameservers for DNS resolution to work. Log in to your domain registrar account and check nameserver settings.
• Check DNS propagation time after making DNS changes. DNS records propagate globally within 72 hours usually but can take up to 48 hours to update everywhere.
• Use online DNS lookup tools to check DNS records from outside your network and confirm resolution works properly everywhere. Useful tools include IntoDNS DNS Checker and DNS Records Explained.
• Change your operating system or router’s default DNS servers to public DNS providers like Cloudflare (1.1.1.1) or Google (8.8.8.8) for faster performance.

And if all else fails, please call your domain registrar or DNS provider’s technical support! They can help investigate harder DNS issues like incorrect TTL values or missing nameserver glue records.

DNS Security Issues and Best Practices

The Domain Name System was built decades ago without security in mind. But given how vital DNS is for routing internet traffic, it has become a major vulnerability exploited by hackers when not properly secured:

DNS Cache Poisoning

Hackers can spoof DNS response packets to trick recursors into caching the incorrect IP for a domain. This allows redirecting traffic from a legitimate site to a malicious copy instead – a technique called DNS cache poisoning.

To prevent cache poisoning, large DNS providers implement query rate limiting combined with randomized port numbers on requests. DNSSEC cryptographic verification of responses also now prevents these spoofing attacks.

DDoS Target

Taking down a domain’s nameservers with distributed denial of service (DDoS) attacks is another common tactic to blackout sites, often used for cyber extortion. Anycast routing combined with large-scale DDoS mitigation helps make modern DNS infrastructure quite resilient to volumetric DDoS floods.

Domain Hijacking

Expired or insecure domain registrar accounts are also targeted for hostile takeover. With access, attackers update the nameservers to redirect all traffic for that domain elsewhere. Enabling registrar locks and two-factor authentication prevents unauthorized transfers or changes.

So in summary – enabling registrar security provisions, keeping software up to date, and choosing managed DNS providers focused on security is your best defense. For ultimate protection, Cloudflare’s free plan adds an extra layer of performance and security to any external DNS.

Public Third-Party DNS Services (Google, Cloudflare, OpenDNS, etc)

In addition to your ISP’s provided DNS servers, public third-parties like Google, Cloudflare, OpenDNS, and Quad9 also offer free alternative public DNS resolvers anyone can use for better security, speed, content filtering, and analytics:

• Google Public DNS – 8.8.8.8 / 8.8.4.4
• CloudFlare – 1.1.1.1 / 1.0.0.1
• OpenDNS Home – 208.67.222.222 / 208.67.220.220
• Quad9 – 9.9.9.9 / 149.112.112.112

Migrating your operating system or router to use alternative public DNS can provide an immediate speed boost and added layers of protection against DNS cache poisoning or if your ISP has unreliable DNS.

Most also provide dynamic security filters against phishing sites or adult content as an extra service. Overall the competition and choice lead to faster, safer DNS globally.

Wrap Up: DNS Crash Course

I hope this breakdown helps explain what DNS is, how it works under the hood, and why it’s a critical internet backbone technology to keep websites, email, and internet services running smoothly every day. Here’s a quick recap:

• DNS translates domain names into IP addresses needed to route internet traffic
• Recursive resolvers handle lookups between different DNS servers to get final answers
• Authoritative nameservers provide the source DNS record for each domain
• Registrars maintain DNS records that control how domain names resolve
• Public DNS services like Cloudflare Speed up DNS queries and security

And with over 330 million registered domains and growing, DNS will only become more important over time for the expanding internet ecosystem. So hopefully you now feel more informed on this behind-the-scenes technology we all use hundreds of times per day without even realizing it!

I included a few relevant links above for additional reading on Cloudflare’s DNS service and DNS in general. Please feel free to reach out if you would like to know more information!.

Neil Beckett

Neil is an accomplished web, designer and developer with over 15 years of experience in creating and optimizing websites for small businesses and online entrepreneurs. Read full bio

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