How long are IPv4 addresses?

An Internet Protocol version 4 (IPv4) address is a 32-bit numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication. This 32-bit address space is defined in the foundational standard for the protocol, RFC 791. The address is typically represented in human-readable, dot-decimal notation, which consists of four octets (8-bit numbers) separated by periods (e.g., 192.168.1.1). Each octet represents 8 bits, and with four octets, the total length is 32 bits (4 x 8 = 32).

B. 64 bits long.

This is incorrect. While 64 bits is a common length for interface identifiers in IPv6, it is not the length of an IPv4 address.

C. 128 bits long.

This is the length of an Internet Protocol version 6 (IPv6) address, which was developed to succeed IPv4 and address its address space exhaustion.

D. 16 bits long.

This is incorrect. 16 bits is the standard length for port numbers used in transport layer protocols like TCP and UDP, not for IP addresses.

1. Postel

J. (Ed.). (1981). RFC 791: Internet Protocol. Internet Engineering Task Force (IETF). In Section 3.1

"Format

" the source and destination address fields in the IP datagram header are explicitly defined as "32 bits." Available at: https://datatracker.ietf.org/doc/html/rfc791

2. Massachusetts Institute of Technology (MIT) OpenCourseWare. (2018). 6.033 Computer System Engineering

Spring 2018. Lecture 13: The Network Layer. The lecture notes state

"An IPv4 address is a 32-bit number that uniquely identifies a host." (See slide on "IP addresses").

3. Kurose

J.

& Ross

K. (2017). Computer Networking: A Top-Down Approach (7th ed.). Pearson. In Chapter 4

"The Network Layer: Data Plane

" Section 4.3.1

"The Internet Protocol (IP)

" it is stated

"The format of the IPv4 datagram is shown in Figure 4.14... Key fields include the 32-bit destination IP address and the 32-bit source IP address."