CN · Application Layer interview questions

42 real CN · Application Layer questions from the Computer Science Fundamentals bank, as asked in Indian campus drives and tech interviews. Every question has a verified answer and an AI-tutor explanation on placd — free to start.

1. What is DNS (Domain Name System)?

Junior
  1. A.the hierarchical system that resolves human-readable domain names into IP addresses
  2. B.a stateless request-response application protocol used to transfer web pages, typically over port 80
  3. C.the response code indicating the requested resource was not found on the server
  4. D.a protocol that downloads email to one client and typically removes it from the server
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3. Which statement is correct?

Junior
  1. A.DNS (Domain Name System) — the negotiation that authenticates the server, agrees on cipher suites, and derives session keys before encryption
  2. B.DNS (Domain Name System) — the response code indicating the request succeeded and the resource is returned
  3. C.DNS (Domain Name System) — a protocol that retrieves email while keeping messages on the server and syncing across devices
  4. D.DNS (Domain Name System) — the hierarchical system that resolves human-readable domain names into IP addresses
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4. What is HTTP?

Junior
  1. A.the protocol that sends and relays outgoing email between mail servers, typically over port 25
  2. B.a protocol that downloads email to one client and typically removes it from the server
  3. C.a stateless request-response application protocol used to transfer web pages, typically over port 80
  4. D.the negotiation that authenticates the server, agrees on cipher suites, and derives session keys before encryption
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6. Which statement is correct?

Junior
  1. A.HTTP — the response code indicating the request succeeded and the resource is returned
  2. B.HTTP — a small piece of state the server stores in the browser to track sessions across stateless requests
  3. C.HTTP — the hierarchical system that resolves human-readable domain names into IP addresses
  4. D.HTTP — a stateless request-response application protocol used to transfer web pages, typically over port 80
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7. What is HTTPS?

Junior
  1. A.the hierarchical system that resolves human-readable domain names into IP addresses
  2. B.a stateless request-response application protocol used to transfer web pages, typically over port 80
  3. C.a protocol that downloads email to one client and typically removes it from the server
  4. D.HTTP layered over TLS to encrypt and authenticate web traffic, typically over port 443
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9. Which statement is correct?

Junior
  1. A.HTTPS — the hierarchical system that resolves human-readable domain names into IP addresses
  2. B.HTTPS — HTTP layered over TLS to encrypt and authenticate web traffic, typically over port 443
  3. C.HTTPS — a resolver chasing the full name chain on the client's behalf and returning the final answer
  4. D.HTTPS — the response code indicating the requested resource was not found on the server
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10. What is FTP (File Transfer Protocol)?

Junior
  1. A.a resolver chasing the full name chain on the client's behalf and returning the final answer
  2. B.the protocol that sends and relays outgoing email between mail servers, typically over port 25
  3. C.a protocol for transferring files using separate control and data connections over ports 21 and 20
  4. D.HTTP layered over TLS to encrypt and authenticate web traffic, typically over port 443
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12. Which statement is correct?

Junior
  1. A.FTP (File Transfer Protocol) — a protocol for transferring files using separate control and data connections over ports 21 and 20
  2. B.FTP (File Transfer Protocol) — the negotiation that authenticates the server, agrees on cipher suites, and derives session keys before encryption
  3. C.FTP (File Transfer Protocol) — HTTP layered over TLS to encrypt and authenticate web traffic, typically over port 443
  4. D.FTP (File Transfer Protocol) — the hierarchical system that resolves human-readable domain names into IP addresses
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13. What is DHCP DORA?

Mid
  1. A.a resolver chasing the full name chain on the client's behalf and returning the final answer
  2. B.the four-step lease handshake of Discover, Offer, Request, and Acknowledge that assigns a host its IP
  3. C.HTTP layered over TLS to encrypt and authenticate web traffic, typically over port 443
  4. D.verbs like GET, POST, PUT, and DELETE that specify the action a request performs on a resource
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15. Which statement is correct?

Mid
  1. A.DHCP DORA — a stateless request-response application protocol used to transfer web pages, typically over port 80
  2. B.DHCP DORA — HTTP layered over TLS to encrypt and authenticate web traffic, typically over port 443
  3. C.DHCP DORA — the negotiation that authenticates the server, agrees on cipher suites, and derives session keys before encryption
  4. D.DHCP DORA — the four-step lease handshake of Discover, Offer, Request, and Acknowledge that assigns a host its IP
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16. What is HTTP methods?

Mid
  1. A.the response code indicating the requested resource was not found on the server
  2. B.verbs like GET, POST, PUT, and DELETE that specify the action a request performs on a resource
  3. C.the response code indicating the request succeeded and the resource is returned
  4. D.a protocol that retrieves email while keeping messages on the server and syncing across devices
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18. Which statement is correct?

Mid
  1. A.HTTP methods — the four-step lease handshake of Discover, Offer, Request, and Acknowledge that assigns a host its IP
  2. B.HTTP methods — a protocol for transferring files using separate control and data connections over ports 21 and 20
  3. C.HTTP methods — a protocol that downloads email to one client and typically removes it from the server
  4. D.HTTP methods — verbs like GET, POST, PUT, and DELETE that specify the action a request performs on a resource
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19. What is HTTP status code 200?

Mid
  1. A.the response code indicating the request succeeded and the resource is returned
  2. B.a protocol for transferring files using separate control and data connections over ports 21 and 20
  3. C.a small piece of state the server stores in the browser to track sessions across stateless requests
  4. D.the protocol that sends and relays outgoing email between mail servers, typically over port 25
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21. Which statement is correct?

Mid
  1. A.HTTP status code 200 — a protocol that downloads email to one client and typically removes it from the server
  2. B.HTTP status code 200 — the hierarchical system that resolves human-readable domain names into IP addresses
  3. C.HTTP status code 200 — a stateless request-response application protocol used to transfer web pages, typically over port 80
  4. D.HTTP status code 200 — the response code indicating the request succeeded and the resource is returned
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22. What is HTTP status code 404?

Mid
  1. A.a stateless request-response application protocol used to transfer web pages, typically over port 80
  2. B.the response code indicating the requested resource was not found on the server
  3. C.verbs like GET, POST, PUT, and DELETE that specify the action a request performs on a resource
  4. D.the four-step lease handshake of Discover, Offer, Request, and Acknowledge that assigns a host its IP
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24. Which statement is correct?

Mid
  1. A.HTTP status code 404 — the response code indicating the requested resource was not found on the server
  2. B.HTTP status code 404 — a protocol that downloads email to one client and typically removes it from the server
  3. C.HTTP status code 404 — a stateless request-response application protocol used to transfer web pages, typically over port 80
  4. D.HTTP status code 404 — a protocol for transferring files using separate control and data connections over ports 21 and 20
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25. What is SMTP?

Mid
  1. A.the response code indicating the requested resource was not found on the server
  2. B.a stateless request-response application protocol used to transfer web pages, typically over port 80
  3. C.the protocol that sends and relays outgoing email between mail servers, typically over port 25
  4. D.a protocol that downloads email to one client and typically removes it from the server
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27. Which statement is correct?

Mid
  1. A.SMTP — a stateless request-response application protocol used to transfer web pages, typically over port 80
  2. B.SMTP — the protocol that sends and relays outgoing email between mail servers, typically over port 25
  3. C.SMTP — the negotiation that authenticates the server, agrees on cipher suites, and derives session keys before encryption
  4. D.SMTP — a small piece of state the server stores in the browser to track sessions across stateless requests
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28. What is IMAP?

Mid
  1. A.the four-step lease handshake of Discover, Offer, Request, and Acknowledge that assigns a host its IP
  2. B.a resolver chasing the full name chain on the client's behalf and returning the final answer
  3. C.a stateless request-response application protocol used to transfer web pages, typically over port 80
  4. D.a protocol that retrieves email while keeping messages on the server and syncing across devices
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30. Which statement is correct?

Mid
  1. A.IMAP — the protocol that sends and relays outgoing email between mail servers, typically over port 25
  2. B.IMAP — the response code indicating the requested resource was not found on the server
  3. C.IMAP — a protocol that retrieves email while keeping messages on the server and syncing across devices
  4. D.IMAP — a resolver chasing the full name chain on the client's behalf and returning the final answer
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