How DNS translates domain names to IPs step by step

TL;DR

DNS translates human readable domain names into machine friendly IP addresses. The resolver acts as a phone book, checking caches then querying root, TLD, and authoritative servers to obtain the IP, which is then returned to the browser to fetch the web page. This process makes accessing websites by name possible.

Transcript

Hey everyone, what is DNS? Have you ever wondered how you   access the web pages that you do almost every other day? I am Pooja, from IBM team and I'm going to explain to you how DNS works. DNS in short is called the Domain Name System. The domain name system translates domain names to IP addresses, and what is a  domain and what is an IP address? ... Read More

Key Insights

• DNS is the system that maps domain names to IP addresses.
• The DNS resolver acts as a phone book between human names and machine addresses.
• DNS lookups begin with the browser cache and may progress to the resolver if needed.
• Root servers guide the lookup to the appropriate top level domain servers.
• Top level domain servers provide referral to authoritative name servers.
• Authoritative name servers hold the actual DNS records to resolve a domain.
• Caching occurs at both browser and resolver levels to speed up repeated requests.
• The final step returns the IP to the browser so it can contact the web server.
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Questions & Answers

Q: What is DNS and why does it exist?

DNS, or Domain Name System, is the system that translates domain names into IP addresses so humans can remember and use names like abc.com while machines use numbers to communicate. The resolver acts as the bridge, using caches and a hierarchy of servers to resolve a domain to the correct IP address. This makes navigating the web practical and scalable.

Q: What role does the DNS resolver play in the lookup process?

The DNS resolver functions as the phone book of the internet. When a user enters a domain, the resolver first checks its own cache for an IP address. If not found, it forwards the request to the next step in the hierarchy, starting with root servers and then moving down to TLD and authoritative name servers to retrieve the IP address.

Q: What happens after the browser checks its cache for a domain?

If the browser cache does not have the IP address, the request is sent to the DNS resolver. The resolver then examines its cache and may query root servers to locate the appropriate top level domain server. This step initiates the path toward the authoritative name server that finally provides the IP address.

Q: What is the function of root servers in DNS?

Root servers are the top level in the DNS hierarchy and do not store the IP for a domain themselves, but they know where to direct requests for the top level domain such as .com. They provide crucial information that allows the resolver to reach the next stage in the lookup process, guiding requests toward the right TLD servers.

Q: What does the Top Level Domain server do in the lookup?

The Top Level Domain server handles information for the top level domain like .com. If it cannot provide the IP address, it can refer the request to the appropriate authoritative name server. It essentially tells the resolver where to go next in the chain to obtain the final IP address.

Q: What is an authoritative name server and what does it provide?

An authoritative name server holds the DNS records for a domain and provides the definitive IP address for that domain. The resolver queries it after being directed by the TLD server, receives the IP address, and then caches it for future requests before sending it back to the user’s browser.

Q: How is the final IP address delivered to the browser?

Once the authoritative name server returns the IP address, the DNS resolver stores it in its cache and sends it back to the web browser. The browser can then contact the web server at that IP address to fetch the website content, completing the lookup process.

Q: Why is caching important in DNS lookups?

Caching speeds up repeated lookups by storing recently resolved IP addresses at both the browser and resolver levels. When a user revisits a domain, the cached IP can be used directly without repeating the entire root, TLD, and authoritative lookup chain, reducing latency and network traffic.

Summary & Key Takeaways

• DNS turns domain names into IP addresses in a multi step lookup, beginning with the browser cache, moving to the DNS resolver, then root servers, top level domain servers, and finally the authoritative name server, which returns the IP address for the user’s browser to connect to the web server.

• The DNS resolver serves as a bridge between human friendly names and numeric IP addresses, using caching at both the browser and resolver levels to speed up repeated requests, and delegating to authoritative servers for new lookups.

• In practice, a user types a domain like abc.com, the system resolves to an IP address through sequential lookups, caches the result, and the browser then connects to the target web server to retrieve content.