Internet Protocol version 6 (IPv6): What is the length of an IPv6 address as defined by the standard?

Introduction / Context:
IPv6 was designed to overcome IPv4 address exhaustion and add features such as simplified header processing and built in multicast and anycast. A fundamental fact is the length of the IPv6 address space.

Given Data / Assumptions:

• An IPv4 address is 32 bits long.
• IPv6 expands the address size to accommodate global growth and hierarchical allocation.
• Address length is expressed in bits, not bytes, in protocol specifications.

Concept / Approach:
IPv6 addresses are 128 bits long. They are commonly represented as eight groups of four hexadecimal digits separated by colons, with rules for zero compression and omission to shorten display while preserving the 128 bit value.

Step-by-Step Solution:

Verification / Alternative check:
Any IPv6 packet capture or RFC reference shows addresses and prefix lengths computed over 128 bits (for example, /64 subnets).

Why Other Options Are Wrong:

• 32 bits is IPv4, not IPv6.
• 128 bytes is incorrect by a factor of eight; addresses are 128 bits.
• 64 bits refers to common subnet size inside IPv6, not the full address length.
• 256 bits is not standard for IPv6.

Common Pitfalls:
Confusing the typical /64 subnet size with total address length; misinterpreting hexadecimal notation as implying bytes rather than bits.

Final Answer:
128 bits