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Application Layer Quiz

Total questions: 125

Worksheet time: 1hrs 3mins

Name
Class
Date
1.

Which layer of the OSI model provides services directly to user applications?

a)

Session Layer

b)

Transport Layer

c)

Application Layer

d)

Network Layer

2.

Which of the following is NOT a function of the Application Layer?

a)

Email communication

b)

Routing data

c)

Domain name resolution

d)

Web browsing

3.

Which protocol is used for browsing websites?

a)

FTP

b)

HTTP

c)

SMTP

d)

DNS

4.

The Application Layer protocols communicate with which OSI layer below them?

a)

Session Layer

b)

Network Layer

c)

Transport Layer

d)

Data Link Layer

5.

Which of the following is an application layer protocol?

a)

IP

b)

ARP

c)

ICMP

d)

SMTP

6.

Which layer does DNS operate in?

a)

Network

b)

Application

c)

Transport

d)

Session

7.

The Application Layer in TCP/IP corresponds to which OSI layers?

a)

Application, Presentation, Session

b)

Transport

c)

Network

d)

Data Link

8.

Which of these is not an Application Layer protocol?

a)

HTTP

b)

TCP

c)

FTP

d)

DNS

9.

What kind of addressing does the Application Layer use?

a)

IP addresses

b)

Application-specific identifiers (e.g., domain names)

c)

MAC addresses

d)

Port numbers

10.

Which protocol is used for resolving domain names?

a)

SMTP

b)

FTP

c)

DNS

d)

HTTPS

11.

What port does HTTP use by default?

a)

443

b)

20

c)

80

d)

53

12.

Which method in HTTP is used to retrieve data from a server?

a)

GET

b)

POST

c)

PUT

d)

DELETE

13.

Which protocol ensures secure HTTP communication?

a)

FTP

b)

HTTPS

c)

DNS

d)

TLS

14.

HTTPS is HTTP over which protocol?

a)

SSH

b)

IPsec

c)

TLS

d)

SSLv2

15.

Which port does HTTPS operate on by default?

a)

25

b)

443

c)

21

d)

53

16.

Which HTTP method is used to submit data to a server?

a)

GET

b)

POST

c)

HEAD

d)

CONNECT

17.

HTTP is considered a ______ protocol.

a)

Stateful

b)

Stateless

c)

Secure

d)

Encrypted

18.

Which protocol handles the TLS handshake in HTTPS?

a)

HTTP

b)

TCP

c)

TLS

d)

FTP

19.

Which version introduced multiplexing in HTTP?

a)

HTTP/1.0

b)

HTTP/2

c)

HTTP/1.1

d)

HTTP/3

20.

What does the HTTP status code 404 mean?

a)

OK

b)

Unauthorized

c)

Not Found

d)

Bad Request

21.

Which component of HTTPS provides encryption and data integrity?

a)

HTTP

b)

TLS

c)

DNS

d)

FTP

22.

What is sent in the first step of TLS handshake?

a)

ServerHello

b)

ClientHello

c)

Certificate

d)

Cipher suite

23.

Which part of HTTPS verifies the identity of the server?

a)

Digital Certificate

b)

IP Address

c)

DNS

d)

Port Number

24.

What is the purpose of header compression in HTTP/2?

a)

Reduce latency

b)

Enable streaming

c)

Secure data

d)

Assign ports

25.

What protocol enables real-time communication over HTTP?

a)

FTP

b)

WebSockets

c)

DNS

d)

POP3

26.

Which port does DNS use?

a)

21

b)

53

c)

80

d)

443

27.

Which DNS record maps a domain to an IPv4 address?

a)

MX

b)

A

c)

AAAA

d)

NS

28.

Which record maps to an IPv6 address?

a)

A

b)

AAAA

c)

MX

d)

CNAME

29.

Which DNS record is used for mail server info?

a)

CNAME

b)

MX

c)

A

d)

TXT

30.

What is the first place checked during DNS resolution?

a)

Local DNS cache

b)

Root server

c)

TLD server

d)

Authoritative DNS server

31.

What type of DNS query expects the full answer from a resolver?

a)

Recursive

b)

Iterative

c)

Broadcast

d)

Forwarding

32.

What DNS technology encrypts queries over HTTPS?

a)

DNSSEC

b)

DoH

c)

DNS over TLS

d)

CDNs

33.

Which component maintains the domain's actual IP records?

a)

Recursive Resolver

b)

Root Server

c)

Authoritative DNS Server

d)

TLD Server

34.

What does a CNAME record do?

a)

Maps alias to canonical domain

b)

Stores IP address

c)

Resolves mail server

d)

Points to DNS server

35.

Which DNS record is queried to find the nameservers?

a)

NS

b)

A

c)

MX

d)

PTR

36.

Which port does FTP control connection use?

a)

20

b)

21

c)

25

d)

53

37.

Which mode in FTP initiates both connections from client side?

a)

Active

b)

Passive

c)

Binary

d)

ASCII

38.

Which command logs into an FTP session?

a)

USER

b)

QUIT

c)

LIST

d)

RETR

39.

Which command uploads a file to server in FTP?

a)

RETR

b)

STOR

c)

LIST

d)

QUIT

40.

Which command lists files in FTP?

a)

USER

b)

LIST

c)

STOR

d)

DATA

41.

Which variant of FTP uses SSH for secure transmission?

a)

SFTP

b)

FTPS

c)

FTP

d)

SCP

42.

Which port does FTP data connection use in active mode?

a)

20

b)

21

c)

22

d)

443

43.

Which FTP variant uses TLS for security?

a)

SFTP

b)

FTPS

c)

HTTP

d)

SSH

44.

What is the purpose of the QUIT command in FTP?

a)

Restart session

b)

Upload file

c)

Change directory

d)

Close connection

45.

What is the difference between active and passive FTP?

a)

Command syntax

b)

Who initiates the data connection

c)

Encryption method

d)

Ports used for control

46.

Which protocol is used for sending emails?

a)

IMAP

b)

POP3

c)

SMTP

d)

HTTP

47.

What is the default unencrypted SMTP port?

a)

587

b)

465

c)

25

d)

21

48.

Which command starts an SMTP session?

a)

HELO

b)

MAIL

c)

RCPT

d)

QUIT

49.

Which SMTP command specifies the sender?

a)

MAIL FROM

b)

RCPT TO

c)

DATA

d)

QUIT

50.

Which protocol is commonly used with SMTP for email retrieval?

a)

FTP

b)

HTTP

c)

IMAP

d)

DNS

51.

What is the purpose of RCPT TO command?

a)

Specifies recipient

b)

Starts message

c)

Terminates session

d)

Authenticates client

52.

What happens during the DATA command in SMTP?

a)

Terminates session

b)

Sends the email content

c)

Authenticates sender

d)

Lists folders

53.

Which port is typically used for SMTP with TLS?

a)

465

b)

587

c)

25

d)

443

54.

SMTP is a ______ protocol.

a)

Push

b)

Pull

c)

Secure

d)

Real-time

55.

What is the primary security reason for TLS 1.3 dropping support for RSA key exchange?

a)

It was too slow

b)

It lacked forward secrecy

c)

It used outdated ciphers

d)

It failed to support ECC

56.

What TLS extension allows multiple HTTPS websites to share the same IP address securely?

a)

ALPN

b)

OCSP

c)

SNI

d)

HSTS

57.

Which of the following BEST explains the benefit of Zero-RTT in TLS 1.3?

a)

Reduces memory usage

b)

Enables faster reconnects

c)

Improves DNS caching

d)

Prevents replay attacks

58.

Which of the following protocols supports transport over UDP instead of TCP?

a)

HTTP/2

b)

FTP

c)

HTTPS

d)

HTTP/3 (QUIC)

59.

What is a major security risk with TLS 1.3's Zero-RTT mode?

a)

Certificate spoofing

b)

Replay attacks

c)

MITM attacks via DNS

d)

Downgrade attacks

60.

What problem in HTTP/1.1 does HTTP/2 multiplexing solve?

a)

Head-of-line blocking

b)

Port exhaustion

c)

Statelessness

d)

Certificate revocation

61.

Why is head-of-line blocking not a problem in HTTP/3?

a)

It uses pipelining

b)

It's built on UDP with QUIC streams

c)

It opens multiple TCP connections

d)

It compresses headers

62.

Which HTTP header is responsible for maintaining persistent connections?

a)

Connection: keep-alive

b)

Content-Length

c)

Accept-Encoding

d)

Transfer-Encoding

63.

ALPN is used during TLS handshake to:

a)

Encrypt headers

b)

Resolve domains

c)

Negotiate application protocol (e.g., HTTP/1.1 vs HTTP/2)

d)

Verify MAC

64.

Why does HTTP/3 achieve lower latency than HTTP/2 in lossy networks?

a)

Uses aggressive retransmission

b)

Avoids TCP's retransmission delays via QUIC

c)

Larger congestion window

d)

Uses asymmetric encryption

65.

Which DNS record maps an alias (like mail.example.com) to the actual domain?

a)

A

b)

CNAME

c)

MX

d)

PTR

66.

What does DNS over HTTPS (DoH) achieve?

a)

Avoids round trips

b)

Encrypts DNS queries over HTTPS

c)

Eliminates recursion

d)

Prevents HTTP spoofing

67.

Your server supports FTP uploads but users can't download files. What should you check first?

a)

File permissions

b)

TLS cert

c)

Passive mode firewall rules

d)

Domain name expiry

68.

Which protocol combination is best suited for sending AND receiving secure emails?

a)

SMTP + POP3

b)

SMTP + FTP

c)

SMTP + IMAP over TLS

d)

DNS + SMTP

69.

How does DNS caching help in scaling a globally distributed application?

a)

Lowers CPU usage

b)

Reduces query latency

c)

Prevents DNS poisoning

d)

Avoids load balancing

70.

Your app can curl an IP, but not the domain name. What's most likely the issue?

a)

HTTPS expired

b)

TLS cipher suite mismatch

c)

DNS resolution failure

d)

Firewall blocked port

71.

A browser shows "NET::ERR_CERT_DATE_INVALID" when loading a secure website. What's the cause?

a)

TLS cipher mismatch

b)

Expired certificate

c)

OCSP failure

d)

DNSSEC error

72.

In a microservice setup, how would you secure communication between services?

a)

Use FTP

b)

Use mutual TLS (mTLS)

c)

SSH tunnels

d)

TCP with firewall

73.

How can you avoid downtime when switching domain traffic to a new IP?

a)

Use FTP

b)

Disable DNS cache

c)

Lower TTL before change

d)

Use POP3

74.

You enabled HTTPS on your web server, but clients still connect via HTTP. What could enforce HTTPS?

a)

OCSP

b)

DNSSEC

c)

TLS 1.3

d)

HTTP Strict Transport Security (HSTS)

75.

What does a CA (Certificate Authority) do?

a)

Encrypts messages

b)

Issues and signs digital certificates

c)

Routes traffic

d)

Provides DNS records

76.

Which field in a certificate holds the domain the certificate is valid for?

a)

Issuer

b)

Key Usage

c)

Common Name (CN) or SAN

d)

Signature

77.

How is integrity maintained in TLS transmissions?

a)

Asymmetric keys

b)

SNI extension

c)

Message Authentication Codes (MAC)

d)

Base64 encoding

78.

A MITM attack is suspected on public Wi-Fi. Which protocol protects against this and how?

a)

DNS - encryption

b)

HTTPS - certificate validation & TLS

c)

FTP - passive mode

d)

SMTP - port 25

79.

Which one prevents an attacker from downgrading a TLS connection to a weaker version?

a)

TLS_FALLBACK_SCSV

b)

ALPN

c)

MAC

d)

DNS TTL

80.

You're using a CDN + HTTPS. What's the benefit of certificate pinning?

a)

Prevents fake certs from being accepted

b)

Caches DNS entries

c)

Improves TLS handshake speed

d)

Hides server IP

81.

Your TLS handshake is failing due to unsupported cipher suites. What should you do first?

a)

Increase DNS TTL

b)

Adjust server TLS configuration to include client-supported ciphers

c)

Change domain

d)

Disable SNI

82.

TLS certificates are updated, but old clients still see expired ones. Why?

a)

DNS hasn't propagated

b)

Server-side caching or CDN not purged

c)

Private key mismatch

d)

Key size too small

83.

How does DNS TTL affect blue-green deployment?

a)

Forces email verification

b)

Controls how fast traffic switches between environments

c)

Enables FTP cache

d)

Invalidates certificates

84.

Which combination makes your API endpoint most secure and production-ready?

a)

HTTP + FTP

b)

HTTPS + DNSSEC + mTLS

c)

FTP + POP3

d)

DNS + SSH + TLS 1.0

85.

What is the purpose of the TCP 3-way handshake?

a)

To terminate the connection

b)

To establish a reliable connection

c)

To compress headers

d)

To avoid routing loops

86.

What causes retransmission in TCP?

a)

Timeout or duplicate ACKs

b)

Port mismatch

c)

UDP handshake failure

d)

Header checksum

87.

What TCP mechanism prevents overwhelming a slower receiver?

a)

RTT estimation

b)

Congestion Avoidance

c)

Flow Control (Sliding Window)

d)

SYN flooding

88.

In TCP, a window size of 0 indicates what?

a)

Receiver can't accept data now

b)

Transmission complete

c)

Packet lost

d)

Sender should close connection

89.

TCP sequence numbers are used to:

a)

Encrypt the packet

b)

Ensure ordered delivery

c)

Validate domain names

d)

Address processes

90.

How many steps are involved in TCP connection termination?

a)

2

b)

4

c)

3

d)

1

91.

What flag is set when closing a TCP connection?

a)

URG

b)

FIN

c)

SYN

d)

PSH

92.

TCP congestion control algorithm that starts slow and grows exponentially:

a)

Slow Start

b)

Additive Increase

c)

Fast Recovery

d)

Linear Scaling

93.

Which algorithm kicks in after triple duplicate ACKs in TCP?

a)

Slow Start

b)

Fast Retransmit

c)

Go-Back-N

d)

Checksum

94.

TCP congestion avoidance grows the window size how?

a)

Exponentially

b)

Linearly

c)

Logarithmically

d)

Statically

95.

When TCP detects loss through timeout, it:

a)

Reduces congestion window

b)

Increases window

c)

Sends duplicate ACKs

d)

Ignores

96.

Which value in TCP header helps implement congestion control?

a)

Port number

b)

Congestion Window (cwnd)

c)

Checksum

d)

TTL

97.

If cwnd = 4, and ACKs for all are received, what will cwnd be next in Slow Start?

a)

5

b)

8

c)

6

d)

3

98.

What TCP strategy prevents the sender from flooding the network?

a)

Port blocking

b)

Congestion control

c)

DNS caching

d)

Header compression

99.

Flow control operates between:

a)

Sender and receiver

b)

Switch and router

c)

Application and transport

d)

DNS and HTTP

100.

Which congestion control phase occurs after loss detection?

a)

Recovery

b)

Transmission

c)

Initiation

d)

Discovery

101.

Which transport layer protocol does NOT guarantee delivery?

a)

TCP

b)

UDP

c)

ICMP

d)

HTTP

102.

What is the size of the UDP header?

a)

20 bytes

b)

8 bytes

c)

12 bytes

d)

16 bytes

103.

UDP is preferred over TCP in which scenario?

a)

Bank transaction

b)

Video streaming

c)

File upload

d)

Web login

104.

Which of these is NOT a field in the UDP header?

a)

Source Port

b)

Length

c)

Sequence Number

d)

Checksum

105.

Which application typically uses UDP?

a)

SSH

b)

DNS

c)

HTTPS

d)

SFTP

106.

UDP is called connectionless because:

a)

It requires more time to connect

b)

It does not establish handshakes

c)

It uses ICMP

d)

It maintains sessions

107.

Which of the following is true about UDP?

a)

Reliable, but unordered

b)

Secure

c)

Low overhead

d)

Uses congestion control

108.

VoIP applications prefer UDP because:

a)

Speed matters more than reliability

b)

It uses SSL

c)

TCP consumes less power

d)

DNS is not needed

109.

Which of the following uses UDP by default?

a)

TFTP

b)

Telnet

c)

SSH

d)

FTP

110.

UDP is best for applications that:

a)

Need error correction

b)

Send small amounts of reliable data

c)

Tolerate packet loss and require speed

d)

Require sequencing

111.

Which is better for sending a large image file?

a)

TCP

b)

UDP

c)

ICMP

d)

FTP over UDP

112.

YouTube streaming prefers:

a)

TCP

b)

UDP

c)

SMTP

d)

ICMP

113.

A multiplayer game would use:

a)

TCP

b)

UDP

c)

FTP

d)

HTTP

114.

Which protocol is suitable for sending secure login details?

a)

TCP

b)

UDP

c)

FTP

d)

SMTP

115.

DNS uses UDP because:

a)

Queries are small and need fast response

b)

It avoids handshake

c)

TCP is slow

d)

TCP fails for port 53

116.

Why does TCP use a 3-way handshake instead of 2-way?

a)

Simpler to implement

b)

To prevent half-open connections & replay

c)

Due to encryption

d)

For port scanning

117.

How does TCP detect packet loss?

a)

TTL

b)

Timeout or triple duplicate ACKs

c)

DNS resolution

d)

Port mismatch

118.

In a video call, packets are lost. Why is UDP still used?

a)

Cheaper than TCP

b)

Delay is worse than occasional loss

c)

UDP is more secure

d)

It uses encryption

119.

How would you secure UDP traffic?

a)

You can't

b)

Use TCP fallback

c)

Use DTLS (Datagram TLS)

d)

Use HTTPS

120.

In what case would you choose TCP over UDP in mobile apps?

a)

Voice streaming

b)

Chat messaging with delivery tracking

c)

Video buffering

d)

Gaming

121.

What causes SYN flood attacks in TCP?

a)

Incomplete handshake

b)

Port blocking

c)

UDP retries

d)

DNS poisoning

122.

In a firewall, port 443 is open. What traffic can pass?

a)

FTP

b)

HTTPS (TCP)

c)

DNS

d)

UDP voice

123.

How does NAT affect UDP traffic in VoIP apps?

a)

Improves latency

b)

Encrypts traffic

c)

May block or reroute due to dynamic port mapping

d)

Forces TCP fallback

124.

You want to build a messaging app. Which transport layer protocol would you choose and why?

a)

TCP - reliability and order

b)

UDP - fast response

c)

ICMP - low latency

d)

SMTP - standard protocol

125.

You need to measure UDP vs TCP bandwidth. Which tool should you use?

a)

iperf3

b)

Wireshark

c)

curl

d)

traceroute