Networks & Security — Practice MCQs (DSSSB TGT CS)
40 original questions styled for teaching exams. Choose the best option.
1. Which network typically spans a single building or campus?
- A) WAN
- B) MAN
- C) LAN
- D) GAN
2. Correct ascending order of network size is:
- A) WAN < MAN < LAN < PAN
- B) PAN < LAN < MAN < WAN
- C) LAN < PAN < WAN < MAN
- D) MAN < LAN < PAN < WAN
3. In a star topology, failure of which device usually brings down the whole network?
- A) One peripheral cable only
- B) Central hub or switch
- C) A single end workstation
- D) A remote printer
4. Number of links required for a full mesh of 5 nodes is:
- A) 5
- B) 8
- C) 10
- D) 20
5. A repeater primarily operates at which OSI layer?
- A) Network
- B) Transport
- C) Physical
- D) Application
6. Which device forwards frames based on MAC addresses?
- A) Hub
- B) Switch
- C) Modem
- D) Repeater
7. A router mainly uses which address type for forwarding decisions?
- A) MAC address
- B) Port number only
- C) IP address
- D) URL string
8. Which device can perform protocol conversion between dissimilar networks?
- A) Hub
- B) Repeater
- C) Gateway
- D) Passive hub
9. How many layers are there in the OSI model?
- A) 4
- B) 5
- C) 6
- D) 7
10. TCP and UDP belong to which OSI layer?
- A) Network
- B) Transport
- C) Session
- D) Data Link
11. In the TCP/IP model, HTTP is placed in the:
- A) Internet layer
- B) Transport layer
- C) Application layer
- D) Network access layer
12. Which protocol is connection-oriented and reliable?
- A) UDP
- B) IP
- C) TCP
- D) ICMP
13. Which is best suited for live video streaming where speed matters more than perfect reliability?
- A) TCP only
- B) UDP
- C) SMTP
- D) FTP
14. Default port number for HTTPS is:
- A) 80
- B) 21
- C) 443
- D) 25
15. SMTP is primarily used to:
- A) Resolve domain names
- B) Assign IP addresses
- C) Send email
- D) Encrypt hard disks
16. DNS mainly converts:
- A) MAC to IP
- B) Domain name to IP address
- C) IP to MAC only
- D) Port to process ID
17. DHCP is used for:
- A) Automatic IP configuration
- B) Encrypting email
- C) Compiling programs
- D) Designing topologies
18. Which IPv4 class has default subnet mask 255.255.255.0?
- A) Class A
- B) Class B
- C) Class C
- D) Class D
19. Which address is private?
- A) 172.32.10.5
- B) 192.168.10.5
- C) 8.8.8.8
- D) 11.0.0.1
20. The address 127.0.0.1 is used for:
- A) Broadcast to all hosts
- B) Multicast
- C) Loopback / localhost
- D) Default gateway only
21. Class D IPv4 addresses are reserved for:
- A) Unicast hosts
- B) Multicast
- C) Private LANs only
- D) Experimental Class E only
22. Internet data communication typically uses:
- A) Circuit switching only
- B) Packet switching
- C) Manual telegraph switching
- D) Exclusive optical circuit always
23. Compared to twisted pair, optical fibre generally offers:
- A) Lower bandwidth and more EMI
- B) Higher bandwidth and immunity to EMI
- C) Shorter maximum distance always
- D) Only analog voice
24. In the CIA triad, “Integrity” means:
- A) Data is always secret from everyone
- B) Data is not altered without detection
- C) Servers never reboot
- D) Users never need passwords
25. A firewall primarily:
- A) Compiles source code
- B) Filters network traffic by rules
- C) Replaces all antivirus software permanently
- D) Assigns MAC addresses
26. Symmetric cryptography uses:
- A) One shared secret key for encrypt and decrypt
- B) Only public keys
- C) No keys at all
- D) Two identical public keys only
27. In asymmetric cryptography, a digital signature is typically created using the sender’s:
- A) Public key
- B) Private key
- C) Session cookie
- D) MAC address
28. Hashing is mainly used to check:
- A) Bandwidth of fibre
- B) Integrity of data
- C) Cable length
- D) Switch port speed
29. Phishing attacks usually aim to:
- A) Upgrade OS legally
- B) Trick users into revealing credentials
- C) Repair hard disks
- D) Increase RAM
30. A DoS attack mainly threatens which CIA property?
- A) Confidentiality only
- B) Integrity only
- C) Availability
- D) Non-repudiation alone
31. A VPN typically provides:
- A) Unencrypted open broadcast
- B) Secure tunnel over a public network
- C) Free antivirus signatures
- D) Physical fibre installation
32. HTTPS uses which security protocol family for the secure channel?
- A) FTP only
- B) SSL/TLS
- C) SMTP
- D) Telnet
33. Which statement about hub vs switch is correct?
- A) Hub isolates collision domains per port like a switch
- B) Switch learns MAC addresses; hub broadcasts to all ports
- C) Hub routes by IP
- D) Switch works only at Application layer
34. Which protocol is commonly used to transfer files and uses ports 20 and 21?
- A) HTTP
- B) FTP
- C) DNS
- D) DHCP
35. Presentation layer in OSI is associated with:
- A) Routing packets
- B) Data format, encryption, compression
- C) Bit signalling on wire only
- D) MAC framing only
36. Which is a guided transmission medium?
- A) Radio waves in open air
- B) Infrared through free space
- C) Optical fibre cable
- D) Satellite microwave path only
37. Non-repudiation in digital signatures means:
- A) Receiver cannot prove sender identity
- B) Sender cannot later deny having signed
- C) Data was never transmitted
- D) Keys were never used
38. Which private range is valid under RFC 1918?
- A) 172.16.0.0 – 172.31.255.255
- B) 172.0.0.0 – 172.15.255.255
- C) 192.169.0.0 – 192.169.255.255
- D) 10.256.0.0 – 10.256.255.255
39. Modem’s basic function is:
- A) Route between VLANs by IP only
- B) Modulate/demodulate digital and analog signals
- C) Store DNS records permanently
- D) Replace firewalls
40. Which pair is correctly matched?
- A) HTTP – port 443
- B) DNS – port 53
- C) SMTP – port 80
- D) HTTPS – port 21
Answer Key
- C — LAN covers a limited local area such as a building or campus.
- B — Personal → local → metro → wide is the standard size order.
- B — Star depends on the central hub/switch; its failure isolates all spokes.
- C — Full mesh links = n(n−1)/2 = 5×4/2 = 10.
- C — Repeaters regenerate signals at the Physical layer.
- B — Switches forward using MAC address tables at Data Link layer.
- C — Routers make Layer-3 decisions using IP addresses.
- C — Gateways interconnect dissimilar networks and can translate protocols.
- D — OSI defines seven layers from Physical to Application.
- B — TCP and UDP are Transport-layer protocols.
- C — In TCP/IP, user services like HTTP sit in the Application layer.
- C — TCP is connection-oriented with acknowledgements and retransmission.
- B — UDP’s low overhead suits latency-sensitive streaming.
- C — HTTPS commonly uses TCP port 443.
- C — SMTP is the standard protocol for sending email.
- B — DNS resolves human-readable names to IP addresses.
- A — DHCP automatically assigns IP, mask, gateway, and often DNS.
- C — Class C default mask is 255.255.255.0 (/24).
- B — 192.168.0.0/16 is a private RFC 1918 range.
- C — 127.0.0.1 is the IPv4 loopback address.
- B — Class D (224–239) is reserved for multicast.
- B — The Internet is based on packet switching.
- B — Fibre offers high bandwidth and is immune to electromagnetic interference.
- B — Integrity ensures data has not been tampered with unnoticed.
- B — Firewalls enforce rules to allow or block traffic.
- A — Symmetric crypto uses one shared secret for both operations.
- B — Signing uses the sender’s private key; verification uses the public key.
- B — Cryptographic hashes detect changes to data.
- B — Phishing social-engineers users into giving away secrets.
- C — DoS floods or disables service, hitting availability.
- B — VPNs create encrypted tunnels across public networks.
- B — HTTPS runs HTTP over SSL/TLS.
- B — Hubs flood; switches learn MACs and forward selectively.
- B — Classic FTP uses 21 (control) and 20 (data).
- B — Presentation handles syntax, encryption, and compression concerns.
- C — Fibre is a guided (wired) medium.
- B — A valid signature binds the act to the private-key holder.
- A — Only 172.16–172.31 is the private Class B block.
- B — Modems convert between digital data and analog line signals.
- B — DNS uses port 53; the other pairings are wrong.