In TCP/IP networking (IPv4), how many bits are assigned to the Internet address of a host, which is used in all communications with that host?

Introduction / Context:
IPv4 addressing is the classic scheme for identifying hosts and interfaces on TCP/IP networks. Each IPv4 address uniquely identifies a destination for packets across routed networks. Knowing the bit-length of this address is a foundational networking fact tested in many exams and interviews.

Given Data / Assumptions:

• The question specifically concerns the IPv4 Internet (not IPv6).
• The address is the one used in all communications with the host.
• We assume standard dotted-decimal notation corresponds to a fixed-length binary address.

Concept / Approach:
IPv4 uses a fixed 32-bit address. In dotted-decimal form, this is written as four octets (for example, 192.168.1.10). The 32-bit space provides approximately 4.29 billion unique combinations (subject to reservation and subnetting). IPv6, by contrast, uses 128 bits, but it is not the subject of this question.

Step-by-Step Solution:

Verification / Alternative check:
Inspect any IPv4 packet capture: fields 'Source Address' and 'Destination Address' are 32 bits each. Networking APIs (for example, sockaddr_in) also model IPv4 addresses as 32-bit values.

Why Other Options Are Wrong:

• 16 - bits / 48 - bits / 64 - bits: These sizes correspond to other identifiers (for example, port numbers are 16-bit; MAC addresses are 48-bit; IPv6 is 128-bit, not 64-bit).
• None of the above: Incorrect because 32 - bits is correct for IPv4.

Common Pitfalls:
Mixing up MAC address length (48 bits) with IP address length (32 bits) or confusing IPv4 with IPv6.

Final Answer:
32 - bits