DNS and how domain resolution works in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary role of a DNS resolver in domain name resolution?

In the process of resolving a domain name to an IP address, what does the DNS resolver do?

A It stores the website content and serves it to the user after resolution.

B It translates the domain name into an IP address by querying DNS servers on behalf of the client.

C It assigns IP addresses to devices within a local network.

D It encrypts the domain name to secure the connection between client and server.

💡 Hint

Think about the component that acts as a middleman between your device and DNS servers.

The DNS resolver acts as an intermediary that takes the domain name from the client and queries DNS servers to find the corresponding IP address.

❓ Architecture

intermediate

Which component is responsible for storing authoritative DNS records for a domain?

In the DNS hierarchy, which server holds the definitive information about a domain's IP address?

A Authoritative DNS server

B Root DNS server

C Recursive resolver

D Caching DNS server

💡 Hint

This server provides the final answer for a domain's IP address.

The authoritative DNS server holds the official DNS records for a domain and provides the final IP address answer.

❓ scaling

intermediate

How does DNS caching improve the scalability of domain resolution?

Consider a large number of users requesting the same domain name. How does DNS caching help handle this load efficiently?

A By increasing the number of root DNS servers to handle more requests.

B By assigning new IP addresses dynamically to reduce server load.

C By encrypting DNS queries to prevent unauthorized access.

D By storing previously resolved IP addresses locally to reduce repeated queries to authoritative servers.

💡 Hint

Think about how repeated requests for the same domain can be answered faster.

DNS caching stores resolved IP addresses temporarily so that repeated requests do not need to query authoritative servers again, reducing load and latency.

❓ tradeoff

advanced

What is a tradeoff when setting a very long TTL (Time To Live) for DNS records?

If a DNS record has a very long TTL, what is a potential downside?

A Changes to the domain's IP address take longer to propagate, causing outdated information to be used.

B It increases the number of DNS queries to authoritative servers.

C It causes DNS resolvers to ignore the record completely.

D It reduces the security of DNS queries by exposing them longer.

💡 Hint

Think about how long cached information stays valid before updating.

A long TTL means DNS records are cached longer, so if the IP address changes, clients may still use the old IP until the cache expires.

❓ estimation

expert

Estimate the number of DNS queries a recursive resolver handles per second if it serves 1 million users daily, each making 100 domain requests, with a cache hit rate of 90%.

Calculate the approximate number of DNS queries sent to upstream servers per second by the recursive resolver.

A Approximately 11,574 queries per second

B Approximately 100,000 queries per second

C Approximately 116 queries per second

D Approximately 10,000 queries per second

💡 Hint

Calculate total daily requests, apply cache hit rate, then divide by seconds in a day.

1 million users * 100 requests = 100 million requests daily. With 90% cache hit, 10% go upstream = 10 million queries daily. Divide by 86,400 seconds/day ≈ 116 queries per second. Check options carefully.