How large is the IP version 4 address field?

The size of an IP version 4 address field is 32 bits. This means that an IPv4 address consists of four groups of eight bits, or what is commonly represented as four decimal numbers separated by periods (for example, 192.168.1.1). Each octet can range from 0 to 255, allowing for a total of approximately 4.3 billion unique addresses (2^32). This limited size is one of the reasons that IPv4 addresses are becoming scarce, leading to the development and adoption of IPv6, which offers a vastly larger address space of 128 bits.

The other options indicate sizes that do not pertain to IPv4. For instance, 64 bits is relevant to certain networking protocols or could refer to IPv6 in a segment context, while 16 bits does not represent any standard IP addressing format. Understanding the 32-bit structure of IPv4 is crucial for grasping networking fundamentals.