In Internet Protocol version 6 (IPv6), how many bits are present in a full IPv6 address field?

Introduction / Context:
IPv6 was introduced to overcome the address exhaustion and limitations of IPv4. One of the most fundamental facts about IPv6 that every networking professional must know is the length of an IPv6 address in bits. This directly affects how many unique addresses are available and how IPv6 subnets are designed.

Given Data / Assumptions:

• We are working with native IPv6 addressing, not IPv4-mapped or tunneled addresses.
• IPv4 addresses are commonly known to be 32 bits long.
• The question asks specifically for the number of bits in a standard IPv6 address.
• No unusual address compression or special forms change the underlying bit length.

Concept / Approach:
An IPv6 address is defined as a 128 bit value. It is usually written as eight groups of four hexadecimal digits separated by colons. Each hexadecimal digit represents four bits, so each group of four hexadecimal digits equals 16 bits. Eight such groups give 8 * 16 = 128 bits total. Even when shorthand notation like zero compression is used, the actual address remains 128 bits internally.

Step-by-Step Solution:
1. Observe the standard textual representation of IPv6, for example 2001:0db8:0000:0000:0000:ff00:0042:8329.2. Count the number of groups: there are eight groups separated by colons.3. Each group contains four hexadecimal digits. Each hexadecimal digit represents four bits.4. Therefore, each group represents 4 * 4 = 16 bits of the address.5. Multiply 16 bits per group by eight groups to get 16 * 8 = 128 bits for the full IPv6 address.

Verification / Alternative check:
Standards documents such as the IPv6 base specification and networking references all state that IPv6 uses 128 bit addresses. You can also verify by converting an IPv6 address to binary and counting the bits: an uncompressed address yields 32 hexadecimal digits, and 32 * 4 equals 128 binary digits.

Why Other Options Are Wrong:
Option A, 24 bits, and option B, 16 bits, are far too small for Internet addressing and are not associated with IP address lengths. Option C, 32 bits, corresponds to an IPv4 address, not an IPv6 address. IPv6 intentionally expanded the address space from 32 to 128 bits to provide an enormous number of unique addresses.

Common Pitfalls:
Some learners mistakenly assume that because IPv4 uses 32 bit addresses, IPv6 might use a modestly larger size such as 64 bits. In reality, 64 bits would still be too small for long term global addressing needs, so IPv6 uses 128 bits. Another source of confusion is the presence of interface identifiers and subnet prefixes, but together these still make up the same 128 bit address.

Final Answer:
128 bits