IP Address Classes

5 minutes 5 Questions

IP Address Classes are the categorical divisions of IPv4 addresses based on their first octet values. These classes are Class A, Class B, Class C, Class D, and Class E. Class A addresses have a range of 1.x.x.x to 126.x.x.x, used for large organizations; Class B addresses encompass 128.x.x.x to 191.x.x.x, meant for medium-sized organizations; Class C addresses range from 192.x.x.x to 223.x.x.x, used for small networks; Class D addresses are utilized for IP multicasting (from 224.x.x.x to 239.x.x.x); and finally, Class E addresses range from 240.x.x.x to 255.x.x.x, reserved for future use and research.

Guide: Understanding IP Address Classes

What are IP Address Classes?
Internet Protocol (IP) Address Classes divide the IP address space into segments. The five classes, identified by the first four bits, are Class A, B, C, D, and E. Class A, B, and C are the most commonly used for network addressing.
Why are IP Address Classes Important?
IP Address Classes play a critical role in organizing the IP address system, distinguishing network address from host address and supporting large, medium, and small networks.
How Do IP Address Classes Work?
Class A holds a large number of IP addresses with a smaller number of networks. Conversely, Class C represents a small number of IP addresses with a large number of networks, while Class B offers a balance between the two. The fifth and sixth classes, D and E, are used for multicast and experimental purposes, respectively.
Exam Tips: Answering Questions on IP Address Classes
Understand the range of each class and know how to recognize an IP address class by just looking at the initial figures. Pay attention to the differences between the classes; this can be key to knowing how many networks or hosts a particular class can provide. Familiarize yourself with Class D and E as they often appear in exams.

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Question 1

An organization has a public-facing web server with the IP address 203.0.113.15. To which IP address class does it belong?

Class A APIPA Class B Class C

Correct Answer: Class C

IP addresses are classified into five classes: A, B, C, D and E. Class A addresses range from 1.0.0.0 to 126.0.0.0, Class B addresses range from 128.0.0.0 to 191.255.255.255, and Class C addresses range from 192.0.0.0 to 223.255.255.255. The given IP address 203.0.113.15 falls within the Class C range, hence the correct answer is 'Class C'. Class A and Class B are incorrect because their respective ranges do not include the given IP address. APIPA (Automatic Private IP Addressing) generates addresses in the range 169.254.0.1 to 169.254.255.254 and is not relevant to this question as the given IP does not fall within this range.

Question 2

A company's network administrator is configuring the network to assign IP addresses to new devices. They have a requirement to provide IP addresses from the Class A private range. Which IP address subnet should be used?

169.254.0.0/16 172.16.0.0/12 192.168.0.0/16 10.0.0.0/8

Correct Answer: 10.0.0.0/8

The question specifies a requirement to provide IP addresses from the Class A private range. The Class A private IP address range is 10.0.0.0 through 10.255.255.255, represented as 10.0.0.0/8 in CIDR notation. Hence, 10.0.0.0/8 should be used. The other options, 172.16.0.0/12 and 192.168.0.0/16, represent Class B and Class C private IP address ranges, respectively, not Class A. The last option, 169.254.0.0/16, is not a private IP address range but rather a link-local address range used when a device can't successfully obtain an IP address from a DHCP server.

Question 3

A network engineer is analyzing a network issue and discovers an IP address assigned to a device is 169.254.30.15. What type of IP address is this, and what is its purpose?

Class B, Private Class C, Public Class A, Public APIPA, Auto-Configuration

Correct Answer: APIPA, Auto-Configuration

The IP address 169.254.30.15 is an Automatic Private IP Addressing (APIPA) address. APIPA is a method of automatic IP address configuration. When a device has APIPA enabled and it can't get an IP address through a DHCP server, it automatically assigns itself an IP address in the range 169.254.0.1 to 169.254.255.254. This is mostly used for local communications within a network when a DHCP server isn't present or not working properly. The other answers are incorrect as they misclassify the IP address as either Class A, Class B, or Class C, none of which pertains to the range used by APIPA.

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