20 Subnetting Questions & Answers

Test your IPv4 Subnetting knowledge with Subnetting Quiz 1! Practice with 20 Subnetting Questions and answer explanations covering subnet masks, IP address classes, binary conversions, network and broadcast addresses, usable host ranges and basic subnetting calculations. Solve Subnetting Practice Questions below and improve your subnetting skills for the CCNA exam and real-world networking.

Subnetting Questions – Quiz 1

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Question 1

Which usable host range contains the IPv4 address 10.145.100.6/27?

A	10.145.100.1 - 10.145.100.255
B	10.145.100.0 - 10.145.100.32
C	10.145.100.1 - 10.145.100.30
D	10.145.100.0 - 10.145.100.63
E	10.145.100.0 - 10.145.100.255

Question 1 Explanation:

The address belongs to 10.145.100.0/27. This subnet has a broadcast address of 10.145.100.31 and a usable host range of 10.145.100.1–10.145.100.30.

Question 2

What is the last usable host address in the network 182.144.10.0/29?

A	182.144.10.6
B	182.144.10.0
C	182.144.10.1
D	182.144.10.255
E	182.144.10.254

Question 2 Explanation:

A /29 subnet contains 8 addresses. The network address is 182.144.10.0, the broadcast address is 182.144.10.7, and the usable range is 182.144.10.1–182.144.10.6.

Question 3

What is the decimal equivalent of the 8-bit binary number 01001010?

A	74
B	142
C	140
D	70
E	72

Question 4

What is the correct binary representation of the subnet mask 255.255.128.0?

A	11111111.11111111.11111111.00000001
B	11111111.11111111.00000000.00000000
C	11111111.11111111.00000001.00000000
D	11111111.11111111.10000000.00000000
E	11111111.11111111.11111111.00000000

Question 5

What is the first usable host address in the network 172.18.16.0/21?

A	172.18.16.0
B	172.18.16.15
C	172.18.16.54
D	172.18.16.1
E	172.18.16.16

Question 5 Explanation:

The network address is 172.18.16.0. The first usable host address is the next address, 172.18.16.1.

Question 6

Which IPv4 prefix length allows both addresses to be used on a modern point-to-point router link without separate network and broadcast addresses?

A	/29
B	/28
C	/30
D	/27
E	/31

Question 6 Explanation:

RFC 3021 allows both IPv4 addresses in a /31 prefix to be used on a point-to-point link, reducing address consumption compared with a traditional /30 subnet.

Question 7

A network engineer needs a subnet that supports at least 50 usable IPv4 host addresses. Which subnet mask provides the smallest suitable subnet?

A	255.255.255.0
B	255.255.255.240
C	255.255.255.128
D	255.255.255.224
E	255.255.255.192

Question 7 Explanation:

A /26 subnet provides 64 total addresses and 62 usable host addresses. A /27 supports only 30 usable hosts, so /26 is the smallest suitable subnet.

Question 8

What is the 8-bit binary equivalent of the decimal number 188?

A	10001111
B	10111100
C	10101100
D	10111101
E	10110000

Question 9

A company divides the network 80.160.0.0/16 into equal-sized /20 subnets. How many subnets are created, and how many usable host addresses are available in each subnet?

A	32 subnets, 4,094 usable hosts
B	16 subnets, 4,094 usable hosts
C	16 subnets, 2,046 usable hosts
D	32 subnets, 2,046 usable hosts
E	8 subnets, 8,190 usable hosts

Question 9 Explanation:

Moving from /16 to /20 borrows 4 bits, creating 2⁴ = 16 subnets. A /20 subnet leaves 12 host bits, providing 2¹² − 2 = 4,094 usable host addresses per subnet.

Question 10

What is the network address of the IPv4 host 100.155.1.0/21?

A	100.155.0.0/21
B	100.155.255.0/21
C	100.155.255.1/21
D	100.155.0.255/21
E	100.155.1.0/21

Question 10 Explanation:

A /21 subnet has a block size of 8 in the third octet. The address 100.155.1.0 belongs to the network 100.155.0.0/21.

Question 11

Which of the following is the correct binary representation of the IPv4 address 201.18.171.15?

A	11001001.00010010.10101011.00001111
B	11001001.00010011.10101011.00001111
C	11001001.00010010.10101010.00001111
D	11001001.00010010.10101011.00011111
E	11001000.00010010.10101011.00001111

Question 12

What is the dotted-decimal subnet mask for an IPv4 /26 prefix?

A	255.255.255.248
B	255.255.255.224
C	255.255.255.240
D	255.255.255.192
E	255.255.255.0

Question 12 Explanation:

A /26 prefix contains 26 network bits. Its subnet mask is 255.255.255.192, leaving 6 bits for host addresses.

Question 13

What is the broadcast address of the IPv4 network 172.18.16.0/21?

A	172.18.255.255
B	172.18.0.255
C	172.18.23.255
D	172.18.25.255
E	172.18.30.255

Question 13 Explanation:

A /21 subnet uses the mask 255.255.248.0, creating blocks of 8 in the third octet. The network spans 172.18.16.0 through 172.18.23.255.

Question 14

Which of the following IPv4 addresses belongs to Class A in classful addressing?

A	10.1.152.8
B	172.8.10.1
C	172.8.202.140
D	192.1.52.5
E	200.55.12.34

Question 15

Which IPv4 address class does 172.16.1.1 belong to in classful addressing?

A	Class E
B	Class C
C	Class B
D	Class A
E	Class D

Question 16

Which IPv4 subnet contains the host address 12.120.1.185/25?

A	12.120.1.0/25
B	12.120.1.128/25
C	12.120.1.1/25
D	12.120.1.64/25
E	12.120.1.192/25

Question 16 Explanation:

A /25 subnet has a block size of 128 in the fourth octet. The address 12.120.1.185 falls within 12.120.1.128–12.120.1.255, so its network address is 12.120.1.128.

Question 17

A network engineer is given the IP address 102.74.200.1/23. Which of the following addresses belongs to the same subnet and can be assigned to a host?

A	102.74.200.0
B	102.74.201.200
C	102.74.201.255
D	102.74.199.254
E	102.74.202.1

Question 17 Explanation:

The IP address 102.74.200.1/23 belongs to the network 102.74.200.0/23, with subnet mask 255.255.254.0. - Network Address: 102.74.200.0 - First Usable Host: 102.74.200.1 - Last Usable Host: 102.74.201.254 - Broadcast Address: 102.74.201.255

Question 18

A network engineer needs to divide 192.168.1.0/24 into at least 5 equal-sized subnets. Which subnet mask provides the maximum number of usable hosts per subnet while meeting this requirement?

A	255.255.255.248
B	255.255.255.224
C	255.255.255.240
D	255.255.255.252
E	255.255.255.254

Question 18 Explanation:

Borrowing 3 bits from a /24 creates 8 subnets. A /27 mask provides 30 usable host addresses per subnet.

Question 19

How many usable IPv4 host addresses are available in a standard subnet with mask 255.255.255.0?

A	2
B	255
C	1
D	254
E	224

Question 19 Explanation:

A /24 subnet has 8 host bits, providing 256 total addresses. Excluding the network and broadcast addresses leaves 254 usable host addresses.

Question 20

A company has the network 192.168.1.0/24 and needs at least 7 equal-sized subnets. Each subnet must support at least 18 usable host addresses. Which subnet mask meets both requirements?

A	255.255.255.248
B	255.255.255.240
C	255.255.255.128
D	255.255.255.192
E	255.255.255.224

Question 20 Explanation:

A /27 mask divides a /24 network into 8 equal-sized subnets, each supporting 30 usable host addresses. This meets both requirements.

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Gokhan Kosem is a Network Engineer, Instructor and the Founder of IPCisco.com with 15+ years of experience in Cisco, Nokia, Huawei, Juniper, Linux, Service Provider Networks, Routing and Switching technologies.

He has worked on the backbone networks of major service providers and network vendors including Nortel, Alcatel-Lucent (Nokia) and has extensive hands-on experience with Cisco, Huawei, Juniper and Nokia networking technologies.

He has trained thousands of networking students worldwide through IPCisco.com, Udemy, books, labs, quizzes, and educational content across multiple social media platforms.

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Subnetting Quiz 1

Subnetting Questions – Quiz 1

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