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Quizzes > Computers & Technology > Computers & IT

How Well Do You Know IP Address Classes?

Think you can spot a Class C IP address? Take the free quiz now!

Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art illustration for IP address quiz on sky blue background

This Class A, B, C IP Address Quiz helps you practice spotting IP classes, first-octet ranges, and default masks. Sort addresses into A/B/C, choose valid network and broadcast values, and see where you need review before an exam or lab. If you want more practice, try our networking quiz next.

What is the first octet range for Class A IP addresses?
192 - 223
1 - 126
224 - 239
128 - 191
In classful networking, Class A addresses use the first octet from 1 to 126. The address 127.x.x.x is reserved for loopback testing. This allocation allows for 126 distinct Class A networks. .
Which default subnet mask corresponds to a Class C network?
255.255.255.0
255.0.0.0
255.255.192.0
255.255.0.0
A default Class C network uses a 24-bit mask, written as 255.255.255.0. This mask leaves 8 bits for host addresses. Class C networks support up to 254 hosts by default. .
Which class does the IP address 150.25.10.5 belong to?
Class D
Class C
Class B
Class A
IP addresses with the first octet from 128 to 191 are Class B. The address 150.25.10.5 falls within that range. Class B uses a default mask of 255.255.0.0. .
What is the default network mask in CIDR notation for Class A?
/32
/16
/8
/24
Class A networks use a fixed /8 mask (255.0.0.0) in classful addressing. This reserves the first 8 bits for the network portion. The remaining 24 bits are for host IDs. .
What is the first assignable host address in the 192.168.1.0 network?
192.168.0.1
192.168.1.255
192.168.1.0
192.168.1.1
In a /24 network, the .0 address is the network ID and .255 is the broadcast. The first usable host is therefore .1. This pattern applies to all default Class C networks. .
Which class includes the IP range 192.0.0.0 to 223.255.255.255?
Class D
Class A
Class C
Class B
Class C addresses span from 192.0.0.0 through 223.255.255.255. They use a default /24 mask. Class D starts at 224.x.x.x and is reserved for multicast. .
What is the broadcast address for the Class A network 10.0.0.0?
10.255.255.255
10.255.0.0
10.0.0.255
10.0.255.255
A Class A network uses a /8 mask, so the broadcast address sets all host bits to 1: 10.255.255.255. The network ID is 10.0.0.0. Hosts range from 10.0.0.1 to 10.255.255.254. .
How many usable hosts are available in a default Class C network?
252
1024
254
256
A Class C network uses 8 host bits, giving 2^8 = 256 addresses. Subtracting the network and broadcast addresses leaves 254 usable hosts. .
What is the default subnet mask for Class B in dotted decimal form?
255.255.255.252
255.255.0.0
255.255.255.0
255.0.0.0
Class B networks use a 16-bit network prefix by default, which is 255.255.0.0. This leaves 16 bits for hosts. .
The IP address 127.0.0.1 is reserved for what purpose?
Loopback testing
Private VPN
Multicast
Broadcast
The 127.0.0.0/8 block is reserved for loopback, allowing a host to send packets to itself. The most common address used is 127.0.0.1. .
How many networks are available in Class A addressing?
128
254
254
126
Class A uses the first octet 1 - 126 for networks, giving 126 usable network IDs (0 and 127 are reserved). .
Which octets represent the network portion in Class B under classful addressing?
Last two octets
First octet only
First two octets
First three octets
Class B reserves 16 bits for the network ID, which correspond to the first two octets. Hosts occupy the remaining two octets. .
Which classful network mask in CIDR notation corresponds to 255.255.0.0?
/32
/24
/8
/16
255.255.0.0 means 16 bits set to 1 for the network portion, which is /16 in CIDR notation (Class B default). .
What is the last usable host address in the 172.16.0.0 network?
172.16.0.254
172.16.255.255
172.16.0.255
172.16.255.254
In a /16 network, the broadcast address is 172.16.255.255 and the first host is .1. Subtracting one from the broadcast gives the last usable host .254. .
Which class uses the network mask 255.0.0.0 by default?
Class D
Class A
Class C
Class B
Class A networks use 8 bits for network ID, which corresponds to 255.0.0.0. This supports very large host blocks. .
How many host bits are there in the default Class B address space?
32
16
8
24
Class B networks use a /16 mask, so there are 16 bits left for host addressing. This allows up to 2^16 - 2 usable hosts. .
What is the wildcard mask for a Class C network?
255.255.0.0
0.0.0.255
255.255.255.0
0.0.255.255
The wildcard mask is the bitwise inverse of the subnet mask. For Class C (255.255.255.0), the wildcard is 0.0.0.255. It's used in access lists. .
In classful addressing, what is the network portion length (in bits) for Class C?
8
32
24
16
Class C allocates 24 bits to the network portion and leaves 8 bits for host addresses. This results in /24 mask (255.255.255.0). .
Given the IP address 192.0.2.130, what is the network address under default classful rules?
192.0.0.0
192.0.2.128
192.0.2.255
192.0.2.0
192.0.2.130 falls into a Class C network, so the /24 network address is 192.0.2.0. The host portion is the last octet. .
How many usable host addresses are there in a default Class B network?
65,536
16,382
16,384
65,534
A Class B network has 16 host bits (2^16 total addresses) minus network and broadcast leaves 65,534 usable hosts. .
Which first-octet range is reserved for multicast addresses?
224 - 239
240 - 255
128 - 191
192 - 223
Class D addresses (multicast) occupy first octet values 224 through 239. They are not used for unicast. .
Which class provides the largest number of networks under classful addressing?
Class D
Class C
Class B
Class A
Class C uses 21 network bits, yielding 2^21 possible networks, more than Class A (2^7) or Class B (2^14). Class D isn't used for unicast networking. .
In classful addressing, which class is best suited for small networks requiring around 100 hosts?
Class D
Class C
Class B
Class A
Class C networks provide 254 usable hosts, ideal for small networks around 100 devices. Class B and A are over-sized for that purpose. .
Which summarized route covers the range 192.168.0.0 to 192.168.3.255 in CIDR notation?
192.168.0.0/23
192.168.0.0/22
192.168.0.0/24
192.168.0.0/21
Four contiguous /24 networks (192.168.0.0 - 192.168.3.255) can be summarized as a /22 block. This allocates 22 bits to the prefix. .
Which summarized address block represents the Class B networks from 172.16.0.0 to 172.31.255.255?
172.16.0.0/16
172.16.0.0/12
172.16.0.0/14
172.16.0.0/20
The block 172.16.0.0 to 172.31.255.255 spans 16 contiguous /16 networks. Summarizing requires a /12 mask (16 network bits). .
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Study Outcomes

  1. Identify IP address classes -

    Pinpoint Class A, B, and C IP address ranges by recognizing their numerical start and end points, ensuring you can classify any class a class b class c ip address accurately.

  2. Differentiate network characteristics -

    Compare key attributes of class a and class b ip address networks, including default subnet masks and host capacities, to understand their ideal use cases.

  3. Determine Class C addresses -

    Apply criteria to decide which ip address is class c among given examples, enhancing your ability to quickly recognize Class C ranges in real-world scenarios.

  4. Apply b class IP range knowledge -

    Use your understanding of b class ip range to design and segment mid-sized networks, balancing the number of subnets and hosts effectively.

  5. Analyze subnetting strategies -

    Break down subnet masks for Class A, B, and C networks to calculate available hosts and network IDs for various CIDR notations.

  6. Evaluate networking scenarios -

    Assess practical network examples to choose the appropriate IP class and subnet configuration, boosting confidence in hands-on networking tasks.

Cheat Sheet

  1. Classful Addressing Fundamentals -

    In classful addressing, the first few bits of an IP dictate its class: 0 for Class A, 10 for Class B, and 110 for Class C. This overview answers the question "what are classes of ip address" and helps you quickly identify the class of any IPv4 address (RFC 791). By remembering "0-1-1" you can decode most IPv4 ranges in seconds.

  2. Class A Range and Default Mask -

    Class A IP addresses span from 1.0.0.0 to 126.255.255.255 with a default subnet mask of 255.0.0.0 (/8). These addresses support over 16 million hosts per network, making them ideal for large-scale infrastructures (Cisco CCNA Guide). For example, 10.100.5.1 falls squarely within the Class A block.

  3. Class B Range and Subnetting -

    The b class ip range covers 128.0.0.0 to 191.255.255.255 using a default mask of 255.255.0.0 (/16), supporting up to 65,534 hosts per network (IETF RFCs). A handy mnemonic is "10" at the start to spot a Class B address instantly. Example: 172.16.254.1 is a common private Class B address.

  4. Class C Range and Common Usage -

    Class C addresses run from 192.0.0.0 to 223.255.255.255 with a default mask of 255.255.255.0 (/24), perfect for small LANs supporting up to 254 hosts (Microsoft Docs). If you ask "which ip address is class c," think of 192.168.1.1 used by most home routers. The "110" prefix offers a quick recognition trick.

  5. Private, Reserved & Subnetting Tips -

    Private IP blocks like 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 are reserved from public routing per RFC 1918 and boost network security. Understanding these and loopback ranges (127.0.0.0/8) is essential for network design and troubleshooting. Combine with CIDR/VLSM techniques to subdivide any class a and class b ip address space efficiently for modern networks.

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