What Is DNS? How the Domain Name System Works
Every time you visit a website, send an email, or use an app that connects to the internet, the Domain Name System (DNS) is working behind the scenes. It is one of the most critical yet invisible components of the internet, translating human-friendly domain names into the numerical IP addresses that computers use to find each other.
The Phone Book Analogy:
DNS is often called the "phone book of the internet." Just as a phone book lets you look up someone's phone number by their name, DNS lets your computer look up a server's IP address by its domain name. When you type www.example.com, DNS translates that into an IP address like 93.184.216.34 so your browser knows where to connect.
How DNS Resolution Works: Step by Step
When you type a domain name into your browser, the resolution process involves multiple steps and servers working together. The entire process typically completes in milliseconds, but understanding each step reveals just how elegant the system is.
The DNS Lookup Process:
- Browser Cache: Your browser first checks its own cache to see if it has recently looked up this domain. If found, the cached IP address is used immediately, and no further lookup is needed.
- Operating System Cache: If the browser cache misses, the request goes to your operating system's DNS resolver cache (also called the stub resolver). The OS maintains its own cache of recent lookups.
- Recursive Resolver: If neither local cache has the answer, your device sends a query to a recursive DNS resolver, typically operated by your ISP or a public DNS service like Google (8.8.8.8) or Cloudflare (1.1.1.1). This server does the heavy lifting of finding the answer.
- Root Name Server: The recursive resolver contacts one of the 13 root name server clusters. The root server does not know the final IP address, but it knows which Top-Level Domain (TLD) servers handle extensions like .com, .org, or .net. It responds with a referral to the appropriate TLD server.
- TLD Name Server: The recursive resolver then queries the TLD server (e.g., the .com TLD server). This server knows which authoritative name server is responsible for the specific domain and responds with a referral.
- Authoritative Name Server: Finally, the recursive resolver contacts the authoritative name server for the domain. This server holds the actual DNS records and responds with the IP address associated with the requested domain name.
- Response Returned: The recursive resolver caches the result (based on the record's TTL value) and sends the IP address back to your device. Your browser then connects to the web server at that IP address to load the website.
About Caching and TTL:
Each DNS record has a Time-to-Live (TTL) value that tells resolvers how long to cache the result. Short TTLs (e.g., 300 seconds) allow faster propagation of changes but increase query load. Long TTLs (e.g., 86400 seconds) reduce load but mean changes take longer to spread. When you update a website's DNS records, the change propagates globally as caches expire, which is why DNS changes can take up to 24-48 hours to fully propagate.
Common DNS Record Types
DNS records are instructions stored on authoritative name servers. Different record types serve different purposes. Here are the most important ones you should know:
| Record Type | Name | Purpose | Example Value |
|---|---|---|---|
| A | Address | Maps a domain to an IPv4 address | 93.184.216.34 |
| AAAA | IPv6 Address | Maps a domain to an IPv6 address | 2606:2800:220:1:248:1893:25c8:1946 |
| CNAME | Canonical Name | Creates an alias pointing to another domain | www.example.com → example.com |
| MX | Mail Exchange | Directs email to the correct mail server | 10 mail.example.com |
| TXT | Text | Stores arbitrary text; used for SPF, DKIM, domain verification | v=spf1 include:_spf.google.com ~all |
| NS | Name Server | Specifies the authoritative name servers for a domain | ns1.example.com |
| SOA | Start of Authority | Contains administrative info about a DNS zone (serial, refresh, retry) | ns1.example.com admin.example.com |
| PTR | Pointer | Reverse DNS: maps an IP address back to a domain name | 34.216.184.93.in-addr.arpa → example.com |
Try It Yourself:
Use our DNS Lookup tool to query any domain's DNS records and see these record types in action.
Types of DNS Servers
The DNS infrastructure relies on several types of servers, each playing a distinct role in the name resolution process.
Recursive Resolver
The recursive resolver is the server your device contacts first (after local caches). It acts as an intermediary between your device and the DNS hierarchy, performing the multi-step lookup on your behalf. It queries root servers, TLD servers, and authoritative servers as needed, then caches the result for future queries.
Examples: Your ISP's DNS server, Google Public DNS (8.8.8.8), Cloudflare DNS (1.1.1.1), Quad9 (9.9.9.9)
Root Name Server
Root name servers sit at the top of the DNS hierarchy. There are 13 root server addresses (labeled A through M), each operated by a different organization and distributed globally using anycast routing for redundancy. They do not store domain records directly but direct queries to the appropriate TLD servers.
Operated by: ICANN, Verisign, NASA, U.S. Army, RIPE NCC, and others
TLD Name Server
TLD (Top-Level Domain) servers manage all domains under a specific extension. The .com TLD server knows about every .com domain. The .org TLD server knows about every .org domain. They respond with the authoritative name server for the queried domain.
Categories: Generic TLDs (.com, .org, .net), Country-code TLDs (.uk, .de, .fr), Sponsored TLDs (.edu, .gov)
Authoritative Name Server
The authoritative name server is the final authority for a domain's DNS records. It stores the actual A, AAAA, MX, CNAME, and other records. When queried, it returns the definitive answer. Domain owners configure their DNS records on these servers, either through their registrar or a third-party DNS hosting provider.
Examples: Cloudflare, AWS Route 53, Google Cloud DNS, your domain registrar's nameservers
DNS Security: Threats and Protections
Because DNS is fundamental to how the internet operates, it is a high-value target for attackers. Understanding DNS security threats and the protections available is important for both individuals and organizations.
Common DNS Threats
DNS Cache Poisoning (Spoofing)
An attacker injects forged DNS records into a resolver's cache, redirecting users to malicious websites even when they type the correct domain name. Victims may unknowingly enter credentials on fake login pages.
DNS Hijacking
Attackers compromise a router, DNS server, or domain registrar account to change DNS settings, redirecting a domain's traffic to an attacker-controlled server. This can be used for phishing, malware distribution, or censorship.
DDoS Attacks on DNS
Distributed Denial of Service attacks flood DNS servers with massive volumes of queries, overwhelming them and making the domains they serve unreachable. The 2016 attack on Dyn DNS took down major websites including Twitter, Netflix, and Reddit.
DNS Security Solutions
DNSSEC (DNS Security Extensions)
DNSSEC adds cryptographic signatures to DNS records, allowing resolvers to verify that the response came from the legitimate authoritative server and has not been tampered with in transit. It protects against cache poisoning and spoofing attacks.
DNS over HTTPS (DoH)
DoH encrypts DNS queries by sending them over HTTPS connections. This prevents eavesdroppers on your network from seeing which domains you are querying. Supported by major browsers including Firefox, Chrome, and Edge.
DNS over TLS (DoT)
DoT wraps DNS queries in TLS encryption, similar to DoH but using a dedicated port (853). It is favored by network administrators because it is easier to identify and manage at the network level compared to DoH traffic.
Common DNS Issues and Troubleshooting
DNS problems are one of the most frequent causes of internet connectivity issues. Here are common problems and how to fix them.
Symptoms of DNS Problems
- Websites fail to load but your internet connection is active
- Browser shows "DNS_PROBE_FINISHED_NXDOMAIN" or "Server not found"
- Some websites load while others do not
- Websites load by IP address but not by domain name
- Slow initial page loads followed by normal speed
Troubleshooting Steps
- Flush your DNS cache:
- Windows: ipconfig /flushdns
- macOS: sudo dscacheutil -flushcache
- Linux: sudo systemd-resolve --flush-caches
- Switch DNS servers: Change to a public DNS like 1.1.1.1 (Cloudflare) or 8.8.8.8 (Google)
- Restart your router: Power cycle your router to clear its DNS cache
- Check DNS with nslookup: Run nslookup example.com to verify if DNS is resolving correctly
- Disable VPN or proxy: These can interfere with DNS resolution
- Check your hosts file: Ensure no manual entries are overriding DNS for the affected domain
Frequently Asked Questions
What happens if DNS stops working?
If DNS stops working, you will not be able to access websites by their domain names. Your browser will display errors like "DNS_PROBE_FINISHED_NXDOMAIN" or "Server not found." However, you could still reach websites by typing their IP addresses directly. DNS outages can be caused by server failures, network issues, misconfigurations, or DDoS attacks targeting DNS infrastructure.
Can I change my DNS server?
Yes, you can change your DNS server at any time. Most devices use your ISP's DNS servers by default, but you can switch to public alternatives like Google DNS (8.8.8.8), Cloudflare DNS (1.1.1.1), or Quad9 (9.9.9.9). You can change DNS settings on individual devices or on your router to affect all devices on your network.
Does DNS affect my internet speed?
DNS can affect how quickly websites begin loading, but it does not change your actual download or upload speed. A faster DNS server resolves domain names more quickly, reducing the initial delay before a page starts loading. Switching from a slow DNS server to a fast one like Cloudflare (1.1.1.1) or Google (8.8.8.8) can noticeably improve the perceived speed of your browsing experience.
Is DNS traffic encrypted?
Traditional DNS traffic is sent in plain text, meaning anyone on your network path can see which domains you are querying. However, modern encrypted DNS protocols address this: DNS over HTTPS (DoH) encrypts DNS queries within HTTPS connections, and DNS over TLS (DoT) wraps DNS queries in TLS encryption. Most major browsers and operating systems now support DoH or DoT.
What is the difference between DNS and a URL?
A URL (Uniform Resource Locator) is the full web address you type into your browser, such as https://www.example.com/page. DNS is the system that translates the domain name portion of that URL (example.com) into the IP address of the server hosting the website. Think of the URL as the complete directions to a specific room in a building, while DNS is the system that converts the building's name into its street address.