Unit 2: APPLICATION LAYER - Practice Quiz

1 What is the primary function of the Domain Name System (DNS)?

2 Which port number is typically used by the DNS protocol?

3 Which protocol is primarily used for sending email messages?

4 Which of the following protocols is used to retrieve emails from a server?

5 What does MIME stand for in the context of email?

6 What is the main purpose of the File Transfer Protocol (FTP)?

7 FTP utilizes two connections for its operation. What are they?

8 The Transport Layer provides logical communication between ____, whereas the Network Layer provides logical communication between ____.

9 In the OSI model, which layer sits directly below the Transport Layer?

10 Which of the following is NOT a typical service of the Transport layer?

11 What mechanism does the Transport Layer use to direct incoming data to the correct application process?

12 TCP is considered a ____ protocol.

13 How many steps are involved in the TCP connection establishment process?

14 What is the minimum size of a standard TCP header?

15 During the TCP 3-way handshake, what flag is set in the very first segment sent by the client to the server?

16 UDP is a ____ protocol.

17 What is the fixed size of the UDP header?

18 Which of the following fields is NOT present in a UDP header?

19 Which Transport Layer protocol would be best suited for real-time video streaming where occasional frame loss is acceptable?

20 What type of DNS record maps a domain name to an IPv4 address?

21 A local DNS server receives a request for a domain name it does not have in its cache. If it uses an iterative query process, what will be its immediate next step?

22 An organization wants its primary domain example.com to point to a mail server hosted at mail.example.com. Which DNS record type should be configured to route emails correctly to this server?

23 If a DNS resource record is cached with a Time-To-Live (TTL) of 3600 seconds, what happens when a client requests the same domain 45 minutes later?

24 A user wants to read their emails from multiple devices, ensuring that marking an email as read on their phone updates the status on their laptop. Which protocol combination is most appropriate for this scenario?

25 SMTP is strictly a 7-bit ASCII protocol. How are modern email clients able to send non-text attachments like images or PDFs over SMTP?

26 In the context of email delivery, what is the primary distinction between a Mail Transfer Agent (MTA) and a Mail Delivery Agent (MDA)?

27 A client behind a strict NAT firewall is trying to download a file from an FTP server. The control connection succeeds, but the data transfer fails. Which mode should the client use to resolve this issue?

28 FTP is described as an 'out-of-band' protocol. What does this mean in the context of file transfers?

29 Unlike HTTP, FTP is a stateful protocol. Which of the following best demonstrates this characteristic?

30 If the Network layer provides logical communication between hosts, what specific logical communication does the Transport layer provide?

31 The Network layer (IP) is an unreliable, best-effort delivery service. How does a transport protocol like TCP provide reliability on top of IP?

32 A web server is handling multiple HTTP requests simultaneously. How does the transport layer demultiplex incoming TCP segments to the correct client session?

33 Which of the following scenarios best highlights the difference between flow control and congestion control in the transport layer?

34 Both TCP and UDP provide multiplexing and demultiplexing. What primary mechanism makes this service possible at the transport layer?

35 During a TCP 3-way handshake, host A sends a SYN segment with sequence number . Host B responds with a SYN-ACK segment. What are the sequence and acknowledgment numbers in host B's response?

36 What is the primary function of the 'Window Size' field in the TCP header?

37 If the 'Data Offset' (Header Length) field in a TCP header has a binary value of 0111, what is the total size of the TCP header in bytes?

38 In the TCP connection teardown process, Host A sends a FIN segment to Host B. Host B receives it and sends an ACK. What is the state of the connection at this exact moment?

39 A UDP datagram carries an application payload of 40 bytes. What will be the value placed in the 'Length' field of the UDP header?

40 Which of the following is true regarding the UDP checksum calculation?

41 In a DNS amplification attack, an attacker exploits the characteristics of the DNS protocol to overwhelm a victim. Which of the following combinations of DNS characteristics and architectural design choices makes this attack highly effective?

42 A local DNS server receives an iterative query for a host. The local server's cache contains an NS record for the authoritative domain with a remaining TTL of 5 seconds, but the corresponding A record for that name server has expired. How must the local DNS server proceed to resolve the query?

43 Consider a scenario where a domain's zone file contains a CNAME record mapping 'www.example.com' to 'server.example.net'. Which of the following configurations violates DNS RFC standards and will likely cause resolution failures?

44 An email with a large binary attachment is encoded using Base64 for transmission via SMTP. If the original binary attachment size is exactly Megabytes, what will be the approximate size of the encoded attachment transmitted over the network, ignoring MIME headers and line break characters?

45 During an SMTP transaction between a sending Message Transfer Agent (MTA) and a receiving MTA, the receiver issues a '452 Requested action not taken: insufficient system storage' reply after the sender issues the DATA command. What is the standard-compliant behavior of the sending MTA?

46 Which of the following best describes how the IMAP protocol handles state transitions when a client successfully authenticates and then selects a specific mailbox?

47 An FTP client behind a strict stateful NAT firewall attempts to download a file from a public FTP server using Active FTP mode. The control connection is established successfully, but the file transfer times out. What is the fundamental reason for this failure?

48 During a massive, multi-hour file transfer over an FTP data connection, the FTP control connection may suddenly be dropped by intermediate stateful firewalls. How can modern FTP clients and servers mitigate this specific issue without aborting the ongoing data transfer?

49 If an IP datagram carrying a large TCP segment is fragmented into three pieces by an intermediate router, how does the destination host's transport layer demultiplex the segment to the correct application socket?

50 Which of the following scenarios best demonstrates a violation of the pure end-to-end principle regarding the relationship between the Transport and Network layers?

51 A custom transport protocol is designed to provide strict flow control but explicitly lacks congestion control. Under which of the following network conditions will this protocol cause severe performance degradation for the entire network?

52 Why is it fundamentally impossible for Internet transport layer protocols (like TCP or UDP) to guarantee a maximum end-to-end delay (delay bounds) for application data?

53 During a TCP SYN flood attack, a server utilizes SYN cookies to avoid allocating state for half-open connections. How does the server encode the necessary connection parameters (like MSS) to reconstruct the state when the final ACK arrives from a legitimate client?

54 Assume a TCP connection is operating over a Gbps link at maximum capacity. The TCP sequence number field is bits long. Approximately how long will it take for the sequence numbers to wrap around (complete one full cycle)?

55 In a TCP header, the Data Offset field is 4 bits long and indicates the size of the TCP header in 32-bit words. If a TCP segment carries the maximum allowable length of TCP Options, what is the value of the Data Offset field in decimal, and what is the size of the TCP Options field in bytes?

56 Two hosts, A and B, perform a 'simultaneous open' in TCP, meaning both send SYN segments to each other simultaneously. What is the correct sequence of state transitions for Host A to establish the connection?

57 Host A initiates an active close on a TCP connection with Host B. After sending the final ACK in the 4-way handshake, Host A enters the TIME_WAIT state for an interval equal to twice the Maximum Segment Lifetime (2MSL). Which of the following is the primary reason for this specific duration?

58 When computing the UDP checksum for an IPv6 packet, the calculation includes a pseudo-header. Which of the following accurately describes a critical difference in the UDP checksum implementation between IPv4 and IPv6?

59 The UDP header contains a -bit Length field. Given that the underlying IPv4 header also contains a Total Length field, the UDP Length field might seem redundant. In which of the following edge cases is the UDP Length field strictly necessary to correctly extract the UDP payload?

60 An application requires sending the largest possible UDP payload in a single, unfragmented standard Ethernet frame (MTU = 1500 bytes) over an IPv4 network without any IP options. What is the exact maximum size of the application data (UDP payload) in bytes?