Understanding the Top 50 Questions and Answers for Subnetting

Understanding the Top 50 Questions and Answers for Subnetting

Author by: Mahesh March 23, 2025 582

Subnetting questions and answers are key to understanding network engineering. For network engineers, system administrators, and networking professionals, understanding subnetting is essential to optimizing IP address allocation, enhancing routing efficiency, and ensuring network security. It plays a crucial role in preparing for certification exams such as CCNA, CCNP , and CCIE.

1. What is subnetting?

Subnetting involves dividing large networks into smaller subnetworks, making management simpler and more efficient. This technique not only improves network performance but also enhances security and reduces network congestion by creating structured and easily manageable address spaces. To help professionals prepare for these exams and improve their skills, we’ve compiled the top 50 subnetting interview questions and answers in a multiple-choice format.


Q1. Host IDs on the LAN Interface


Question: Your router has the IP address 172.16.2.1/23 on Ethernet 0. On the LAN interface, which of the following host IDs can be legitimate?
Options:
  1. 172.16.1.100
  2. 172.16.1.198
  3. 172.16.2.255
  4. 172.16.3.0
Answer Options:
  • (A) 1 Only
  • (B) 2 and 3 Both
  • (C) 3 and 4 Both
  • (D) None of the above
Correct Answer: Option C

Q2. Composite IP Addressing Challenges

Part 1: IP Address Analysis


Q3. Question: Which two statements describe the IP address 10.16.3.65/23?
Statements:
  1. 10.16.3.0 is the subnet address, and the mask is 255.255.254.0.
  2. The lowest host address in the subnet is 10.16.2.1 with mask 255.255.254.0.
  3. The last valid host address in the subnet is 10.16.2.254 with mask 255.255.254.0.
  4. The broadcast address of the subnet is 10.16.3.255 with mask 255.255.254.0.
Answer Options:
  • (A) 1 and 3
  • (B) 2 and 4
  • (C) 1, 2 and 4
  • (D) 2, 3 and 4
Correct Answer: Option B

Part 2: Broadcast Address Calculation


Q4. Question: What is the broadcast address of the network 192.168.116.64 with mask 255.255.255.224?
Answer: 192.168.116.95

Part 3: First Valid Host Determination


Q5. Question: Which subnetwork's first legitimate host is the node 172.20.225.111 with mask 255.255.255.128 a part of?
Answer: 172.20.225.1

Q6. Valid Host Range for a /27 Network

Question: The IP address 192.168.187.233/27 belongs to which valid host range?
Answer: 192.168.187.225 through 192.168.187.254

Q7. Default Network Mask for Class A

Question: For CLASS A, the default network mask is:
Options:
  • (A) 255.0.0.0
  • (B) 255.255.0.0
  • (C) 255.255.255.0
  • (D) 255.255.255.255
Answer: Option A

Q8. Default Network Mask for Class B

Question: For CLASS B, the default network mask is:
Answer: Option B

Q9.Default Network Mask for Class C

Question: For CLASS C, the default network mask is:
Answer: Option C

Q10. Maximum Hosts on a /27 Subnet

Question: What is the maximum number of IP addresses available for hosts on a subnet using the 255.255.255.224 mask?
Options:
  • (A) 14
  • (B) 15
  • (C) 30
  • (D) 62
Answer: Option C

 Q11. Testing the IP Stack on Your Local Host

Question: To test the IP stack on your local host, which IP address should you ping?
Options:
  • (A) 127.0.0.0
  • (B) 1.0.0.127
  • (C) 127.0.0.1
  • (D) 255.255.255.0
Answer: Option A

Q12. Subnetting for 5 Subnets with 16 Hosts Each

Question: You need to subnet a network into 5 subnets, each supporting at least 16 hosts. Which configuration will you choose?
Answer: Use a /28 subnet mask (255.255.255.240), which provides 16 subnets with 14 usable hosts each. This meets the requirement of at least 5 subnets with 16 hosts (including network and broadcast addresses)

Q13. Determining the Subnetwork Number

Question: What is the subnetwork number for a host with the IP address 172.16.66.0/21?
Answer: The subnet number is 172.16.64.0/21. This is determined by finding the subnet range, where 172.16.64.0 – 172.16.71.255 is the valid subnet block.

Q14. Subnets and Hosts from a /30 Network

Question: How many subnets and hosts per subnet can you get from the network 192.168.212.0 with mask 255.255.255.252?
Answer: A /30 subnet provides 64 (2⁶) subnets and 2 usable hosts per subnet (4 total addresses, minus 2 for network and broadcast).

Q15. Broadcast Address for a /26 Network

Question: What is the broadcast address of the network 192.168.72.64 with mask 255.255.255.192? Answer: The broadcast address for the network 192.168.72.64/26 (mask 255.255.255.192) is 192.168.72.127. It is the last IP in the subnet range 192.168.72.64 - 192.168.72.127.

Q16. Identifying the Subnet for a Host

Question: Which subnet does host 172.23.184.110 with mask 255.255.255.224 belong to?
Answer: 172.23.184.96

Q17. Broadcast Address for a /28 Network

Question: What is the network 192.168.79.48/28's broadcast address?
Answer: 192.168.79.63

Q18. Last Valid Host in a /28 Subnet

Question: What is the last valid host on the subnetwork 172.19.219.160 with mask 255.255.255.240?
Answer: 172.19.219.174

Q19. Broadcast Address with a /27 Mask

Question: What is the broadcast address of the network 172.18.107.0 with mask 255.255.255.224?
Answer: 172.18.107.31

Q20. First Valid Host in a /22 Subnet

Question: Which subnetwork's first legitimate host is the one to which node 172.31.148.112/22 belongs?
Answer: 172.31.148.1

Q21. Broadcast Address for a /23 Network

Question: What is the network 172.18.120.0/23's broadcast address?
Answer: 172.18.121.255

Q22. Last Valid Host in a /22 Subnet

Question: What is the last valid host on the subnetwork 172.22.232.0 with mask 255.255.252.0?
Answer: 172.22.235.254

Q23. Determining the Subnet for an IP

Question: Which subnet does host 192.168.39.227 with mask 255.255.255.224 belong to?
Answer: 192.168.39.224

Q24. Broadcast Address Calculation

Question: What is the broadcast address of the network 172.18.105.64 with mask 255.255.255.224?
Answer: 172.18.105.95

Q25. First Valid Host Determination

Question: Which subnetwork is the first valid host in the one that contains the node 172.19.24.234 with mask 255.255.240.0?
Answer: 172.19.16.1

Q26. Designing a Subnet Mask for Specific Needs

Question:
For the 172.16.0.0 network, you are creating a subnet mask. To achieve 80 subnets with up to 300 hosts per subnet, which subnet mask should you use?
Answer: 255.255.254.0

Q27. Last Valid Host in a /24 Subnet (172.16.22.0)

Question: What is the subnetwork 172.16.22.0/24's last operational host?
Answer: 172.16.22.254

Q28. Last Valid Host in a /24 Subnet (172.17.126.0)

Question:
Which host on the subnetwork 172.17.126.0/24 is the last one still in use?
Answer: 172.17.126.254
Q29. Subnets and Hosts from a /20 Network
Question: How many subnets and hosts per subnet can be obtained from the network 172.28.0.0 with mask 255.255.240.0?
Answer: 16 subnets and 4094 hosts

Q30. Broadcast Address for a /20 Network

Question: What is the broadcast address of the network 10.230.32.0 with mask 255.255.240.0? Answer: 10.230.47.255

Q31. Valid Host Range for a /27 Network (192.168.185.149)

Question: What valid host range is the IP address 192.168.185.149/27 part of?
Answer: 192.168.185.129 through 192.168.185.158

Q32. Broadcast Address for a /20 Network (10.149.208.0)

Question: What is the network 10.149.208.0/20's broadcast address?
Answer: 10.149.223.255

Q33. Subnets and Hosts from a /30 Network (192.168.129.0)

Question: Can you use mask 255.255.255.252 to extract the number of hosts and subnets from the network 192.168.129.0?
Answer: 64 subnets and 2 hosts

Q34. First Valid Host in a /24 Subnet (172.31.128.16)

Question: What is the first valid host on the subnetwork that the node 172.31.128.16 with mask 255.255.255.0 belongs to?
Answer: 172.31.128.1

Q35. Subnets and Hosts from a /28 Network (172.26.0.0)

Question:  How many hosts and subnets can you obtain from the 172.26.0.0/28 network?
Answer: 4096 subnets and 14 hosts

Q36. First Valid Host in a /20 Subnet (172.30.241.75)

Question: Which subnetwork's first legitimate host is the node 172.30.241.75 with mask 255.255.240.0 a part of?
Answer: 172.30.240.1

Q37. Broadcast Address for a /28 Subnet (192.168.121.112)

Question: What is the network 192.168.121.112's broadcast address with mask 255.255.255.240?
Answer: 192.168.121.127

Q38. First Valid Host in a /23 Subnet (172.25.85.103)

Question: Which subnetwork's first legitimate host is the node 172.25.85.103 with mask 255.255.254.0 a part of?
Answer: 172.25.84.1

Q39. Last Valid Host in a /24 Subnet (172.30.67.0)

Question: What is the subnetwork 172.30.67.0/24's last working host?
Answer: 172.30.67.254

Q40. First Valid Host in a /26 Subnet (172.31.242.158)

Question: What is the first valid host on the subnetwork that the node 172.31.242.158 with mask 255.255.255.192 belongs to?
Answer: 172.31.242.129

Q41. Last Valid Host in a /23 Subnet (172.29.4.0)

Question: What is the last operational host for the subnetwork 172.29.4.0/23?
Answer: 172.29.5.254

Q42. Subnets and Hosts from a /23 Network (172.16.0.0)

Question: How many subnets and hosts per subnet can you obtain from the network 172.16.0.0/23?
Answer: 128 subnets and 510 hosts

Q43. Last Valid Host in a /28 Subnet (172.22.94.144)

Question: What is the last valid host on the subnetwork 172.22.94.144 with mask 255.255.255.240?
Answer: 172.22.94.158

Q44. Designing a Subnet Mask for 100 Subnets and 400 Hosts

Question: For the 172.21.0.0 network, you require 100 subnets with up to 400 hosts each. Which subnet mask should you use?
Answer: 255.255.254.0

Q45. Broadcast Address for a /20 Network (172.29.144.0)

Question: What is the broadcast address of the network 172.29.144.0/20?
Answer: 172.29.159.254

Q46. Valid Host Range for a /24 Network (172.19.89.228)

Question: What is the range of valid hosts that includes the IP address 172.19.89.228/24?
Answer: 172.19.89.1 through 172.19.89.254

Q47. Last Valid Host in a /24 Subnet (172.28.99.0)

Question: What is the subnetwork 172.28.99.0/24's last working host?
Answer: 172.28.99.254

Q48. Identifying the Subnet for a Host (192.168.69.15)

Question: Which subnet does host 192.168.69.15 with mask 255.255.255.224 belong to?
Answer: 192.168.69.0

Q49. First Valid Host in a /26 Subnet (172.19.102.122)

Question: Which host is the first legitimate host in the subnetwork that contains the node 172.19.102.122/26?
Answer: 172.19.102.65

Q50. First Valid Host for a /24 Network (172.122.18.0)

Question: What is the first valid host for the network 172.122.18.0/24?
Answer: 172.122.18.1

Conclusion

Subnetting is a key part of working with networks. This guide is part of a CCNA course and includes 50 important questions and answers about subnetting. These questions help you learn how to break large networks into smaller parts. They show you how to set up IP addresses and use subnet masks correctly. Using this guide, you can learn to create secure and fast networks. It is a helpful tool for students and anyone studying for CCNA, CCNP , or CCIE exams. By practicing these questions, you will build a strong base in networking. With clear steps and simple examples, you can become a confident network expert and become a pro.

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