Topic in Computer Networks & Cloud Computing
The application layer is the top layer of the network stack, where protocols such as HTTP, DNS and SMTP provide services directly to user programs. Expect questions on DNS resolution, record types like A, AAAA, CNAME, MX and NS, and its default port 53. Web topics include HTTP methods and status codes, the Host header, persistent connections, cookies, HTTP/2 multiplexing and HTTPS. Email items cover SMTP for sending versus POP3 and IMAP for retrieval, while file transfer questions compare FTP active and passive modes with SFTP. Client-server versus peer-to-peer models, DHCP, and full-duplex WebSocket connections also appear.
Below are 30 practice questions from a pool of 210 Application Layer MCQs, one of 10 topics in Computer Networks & Cloud Computing. Each shows the correct answer with an explanation; when you are ready, take a timed quiz to test recall under exam conditions.
Each question below shows the correct answer with a full explanation. Use these to build conceptual understanding before attempting a timed quiz.
Q1. What is Telnet used for?
Telnet is used for remote login to access and manage network devices. However, it transmits data in plain text and has been largely replaced by SSH.
Q2. What does DNS stand for?
DNS stands for Domain Name System. It translates human-readable domain names (like www.example.com) into IP addresses.
Q3. Which protocol is used to retrieve emails from a mail server while keeping them on the server?
IMAP (Internet Message Access Protocol) allows users to access emails on the server without downloading them, keeping them synchronized across multiple devices.
Q4. Which port does SSH use?
SSH (Secure Shell) uses port 22. It provides encrypted remote access to network devices and servers.
Q5. What does URL stand for?
URL stands for Uniform Resource Locator. It specifies the address of a resource on the Internet, including the protocol, domain, and path.
Q6. Which protocol does a web browser use to access websites?
Web browsers primarily use HTTP or HTTPS to request and receive web pages from web servers.
Q7. What port does FTP use for control connection?
FTP uses port 21 for the control connection (commands and responses) and port 20 for the data connection.
Q8. Which protocol is used to send emails?
SMTP (Simple Mail Transfer Protocol) is used to send emails from a client to a server or between mail servers.
Q9. What is HTTP?
HTTP (HyperText Transfer Protocol) is the foundation of data communication on the World Wide Web, used for transferring web pages and resources.
Q10. What port does SMTP use?
SMTP uses port 25 for communication between mail servers. Port 587 is used for mail submission from clients.
Q11. What is a RESTful API?
A RESTful API follows REST (Representational State Transfer) principles, using standard HTTP methods (GET, POST, PUT, DELETE) for stateless, resource-based client-server interactions.
Q12. What is the difference between FTP active and passive modes?
In active FTP, the server connects back to the client for data transfer. In passive FTP, the client initiates both control and data connections, which works better with firewalls.
Q13. What is a MIME type used for in email?
MIME (Multipurpose Internet Mail Extensions) types describe the format of email content, enabling emails to contain multimedia content like images, audio, and attachments.
Q14. What is the key improvement in HTTP/2 over HTTP/1.1?
HTTP/2 introduces binary framing and multiplexing, allowing multiple requests and responses to be interleaved over a single TCP connection, eliminating head-of-line blocking at the application layer.
Q15. What is the purpose of DNSSEC?
DNSSEC (DNS Security Extensions) adds digital signatures to DNS responses, enabling clients to verify the authenticity and integrity of DNS data, preventing cache poisoning attacks.
Q16. What is the role of a DNS resolver?
A DNS resolver receives queries from clients and recursively queries DNS servers to translate domain names into IP addresses.
Q17. What HTTP status code indicates 'Not Found'?
HTTP 404 means the requested resource was not found on the server. 200 is OK, 301 is Moved Permanently, and 403 is Forbidden.
Q18. What is DNS-over-HTTPS (DoH)?
DNS-over-HTTPS sends DNS queries and responses over HTTPS, encrypting them to prevent eavesdropping and manipulation by middleboxes, enhancing user privacy.
Q19. In HTTP, what is the purpose of the ETag header?
ETag is a validator that identifies a specific version of a resource. Clients can use it with If-None-Match to check if a cached resource is still valid, reducing bandwidth.
Q20. What is the difference between HTTP/1.1 persistent and non-persistent connections?
Persistent connections (default in HTTP/1.1) keep the TCP connection open for multiple requests, reducing connection setup overhead. Non-persistent opens and closes a connection for each request.
Q21. What is the purpose of DNS caching?
DNS caching stores recently resolved name-to-address mappings locally, reducing query time and DNS server load for subsequent requests for the same domain.
Q22. In DNS, what is a recursive query?
In a recursive query, the DNS server takes full responsibility for resolving the domain name. It queries other DNS servers as needed and returns the final answer to the client.
Q23. In HTTP, what is the difference between GET and POST methods?
GET is used to retrieve data and parameters are visible in the URL. POST submits data in the request body, making it more suitable for sensitive data and large payloads.
Q24. What type of DNS record maps a domain name to an IPv4 address?
An A (Address) record maps a domain name to an IPv4 address. AAAA records map to IPv6, MX records point to mail servers, and CNAME records create aliases.
Q25. What is DNS amplification attack?
DNS amplification is a DDoS attack where an attacker sends DNS queries with a spoofed source IP (victim's IP) to open resolvers. The large DNS responses flood the victim.
Q26. Which protocol is used for secure file transfer?
SFTP (SSH File Transfer Protocol) provides secure file transfer by running over SSH, encrypting both commands and data.
Q27. What is SNMP used for?
SNMP (Simple Network Management Protocol) is used to manage and monitor network devices such as routers, switches, servers, and printers.
Q28. What is the function of a reverse proxy?
A reverse proxy sits in front of backend servers, distributing incoming requests among them. It provides load balancing, SSL termination, caching, and hides backend server details.
Q29. What is WebSocket and how does it differ from HTTP?
WebSocket establishes a persistent, full-duplex communication channel over a single TCP connection, allowing both server and client to send data independently, unlike HTTP's half-duplex request-response pattern.
Q30. What is the purpose of a CDN (Content Delivery Network)?
A CDN places copies of content on servers distributed globally, serving users from the nearest server to reduce latency, improve load times, and handle traffic spikes.
Take a timed quiz drawn from 210+ questions on this topic. No signup required — your progress saves in your browser.
Start Application Layer Quiz