In IPv4 addressing, how long is an IPv4 address and how is this length usually expressed?

Introduction / Context:
Every device on an IPv4 network is assigned a unique IP address that identifies it at the network layer. The size of this address determines how many distinct addresses are possible and influences the design of the protocol. This question asks how long an IPv4 address is and tests basic familiarity with IPv4 addressing fundamentals.

Given Data / Assumptions:

• The focus is specifically on IPv4, not IPv6.
• IPv4 addresses are commonly written in dotted decimal notation such as 192.168.1.10.
• This notation represents underlying binary values.
• The question requires the length expressed in bits or bytes.

Concept / Approach:
An IPv4 address consists of 32 bits. These 32 bits are often grouped into four octets of 8 bits each. Each octet is converted to its decimal equivalent and written as a number between 0 and 255, with dots separating the octets. This yields the dotted decimal notation that users see. Because there are 32 bits, the total number of unique addresses in the theoretical IPv4 address space is 2 raised to the power 32. Understanding that the length is 32 bits is essential for subnetting calculations and capacity planning.

Step-by-Step Solution:
Step 1: Recall that IPv4 addresses are grouped into four octets when written in human readable form.Step 2: Remember that an octet is 8 bits long.Step 3: Multiply four octets by 8 bits per octet to obtain 32 bits in total.Step 4: Recognize that 32 bits is equal to 4 bytes, since one byte contains 8 bits, but the standard way to express IPv4 address size is in bits.Step 5: Conclude that the correct answer is 32 bits, not 32 bytes or any 128 bit value.

Verification / Alternative check:
IPv4 related documentation and standards repeatedly state that IPv4 uses 32 bit addresses. Subnet masks are also 32 bits long, and CIDR notation expresses prefixes as /8, /16, /24, and so on, all within a 32 bit address space. The common statement that IPv4 supports about four billion addresses comes from the fact that 2 raised to the power 32 is slightly more than four billion, further confirming the address length.

Why Other Options Are Wrong:
Option A, 128 bytes, is far too large and would correspond to 1024 bits, not used for IPv4 addressing. Option C, 32 bytes, would represent 256 bits, which is also incorrect for IPv4. Option D, 128 bits, corresponds to IPv6 address length, not IPv4. Only 32 bits correctly describes the size of an IPv4 address.

Common Pitfalls:
A frequent confusion is between IPv4 and IPv6 lengths, especially because both are widely discussed. Students may also see the four decimal numbers and think in terms of bytes instead of bits. Remembering that each dotted decimal number represents 8 bits and that there are four such numbers makes it easy to multiply and get 32 bits. Keeping IPv4 as 32 bits and IPv6 as 128 bits in mind is a useful memory anchor.

Final Answer:
An IPv4 address is 32 bits long, which is the correct length for IPv4 addressing.