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The Length of an IPv6 Address (IPv6 Addressing Fundamentals)

The Length of an IPv6 Address (IPv6 Addressing Fundamentals)

Verified Sources
Nov 4, 2026

An IPv6 address is 128 bits long, which corresponds to 16 bytes. This is a defining property of IPv6 (contrasting with IPv4’s 32-bit addresses).3

Key terms (to anchor the concepts)

  • IPv6 address
  • bit
  • byte
  • interface identifier

A useful way to remember it is:

  • 128128 bits == 1616 bytes (since 11 byte == 88 bits).

Mermaid visualization of the size:

Footnotes

  1. Wikipedia — IPv6 (addressing overview). https://en.wikipedia.org/wiki/IPv6 - States IPv6 uses 128-bit addresses (commonly summarized). ↩ ↩2

  2. RFC 5952 or related IPv6 textual representation guidance (hex groups, zero compression). https://www.rfc-editor.org/rfc/rfc5952 - Describes IPv6 address textual form and compression rules without changing length. ↩

  3. RFC 4291 — IP Version 6 Addressing Architecture (IPv6 address length definition). https://www.rfc-editor.org/rfc/rfc4291 - Defines the structure/architecture of IPv6 addressing, including the 128-bit address length. ↩

IPv6 Addressing (128-bit addresses) — Learning Resource

Understanding Why IPv6 Uses 128 Bits

IPv6 was designed with a vastly larger address space than IPv4. The 128-bit size is what makes that expansion possible and is specified in core IPv6 specifications.2

In IPv6, addresses are commonly described as being structured into parts (e.g., a network prefix and an interface identifier), but no matter how you format or split them conceptually, the total length remains 128 bits.2

Mermaid concept map:

Formatting note (important for exams)

Even though IPv6 is typically written in hexadecimal and often using shorthand like ::, those are presentation conventions. They do not change the underlying address length, which stays at 128 bits.2

Footnotes

  1. Wikipedia — IPv6 (addressing overview). https://en.wikipedia.org/wiki/IPv6 - States IPv6 uses 128-bit addresses (commonly summarized). ↩

  2. RFC 4291 — IP Version 6 Addressing Architecture (IPv6 address length definition). https://www.rfc-editor.org/rfc/rfc4291 - Defines the structure/architecture of IPv6 addressing, including the 128-bit address length. ↩ ↩2 ↩3

  3. RFC 5952 or related IPv6 textual representation guidance (hex groups, zero compression). https://www.rfc-editor.org/rfc/rfc5952 - Describes IPv6 address textual form and compression rules without changing length. ↩ ↩2

How to Select the Correct Multiple-Choice Option

  1. 1
    Step 1

    Use the specification fact: an IPv6 address is 128 bits long.2

    Footnotes

    1. Wikipedia — IPv6 (addressing overview). https://en.wikipedia.org/wiki/IPv6 - States IPv6 uses 128-bit addresses (commonly summarized). ↩

    2. RFC 4291 — IP Version 6 Addressing Architecture (IPv6 address length definition). https://www.rfc-editor.org/rfc/rfc4291 - Defines the structure/architecture of IPv6 addressing, including the 128-bit address length. ↩

  2. 2
    Step 2

    Choose (iii) 128 bits.

  3. 3
    Step 3

    Reject (i) 32 bits (IPv4-like size) and (ii) 64 bits / (iv) 256 bits (not IPv6’s defined length).2

    Footnotes

    1. Wikipedia — IPv6 (addressing overview). https://en.wikipedia.org/wiki/IPv6 - States IPv6 uses 128-bit addresses (commonly summarized). ↩

    2. RFC 5952 or related IPv6 textual representation guidance (hex groups, zero compression). https://www.rfc-editor.org/rfc/rfc5952 - Describes IPv6 address textual form and compression rules without changing length. ↩

Exam Shortcut

If a question asks only the length of an IPv6 address, the answer is always 128 bits—formatting rules (like ::) don’t affect length.2

Footnotes

  1. Wikipedia — IPv6 (addressing overview). https://en.wikipedia.org/wiki/IPv6 - States IPv6 uses 128-bit addresses (commonly summarized). ↩

  2. RFC 4291 — IP Version 6 Addressing Architecture (IPv6 address length definition). https://www.rfc-editor.org/rfc/rfc4291 - Defines the structure/architecture of IPv6 addressing, including the 128-bit address length. ↩

Common Confusion

Many learners confuse the number of hexadecimal characters/groups shown with the underlying bit-length. IPv6 notation can look different (compression, leading-zero suppression), but the address is still 128 bits.2

Footnotes

  1. RFC 5952 or related IPv6 textual representation guidance (hex groups, zero compression). https://www.rfc-editor.org/rfc/rfc5952 - Describes IPv6 address textual form and compression rules without changing length. ↩

  2. RFC 4291 — IP Version 6 Addressing Architecture (IPv6 address length definition). https://www.rfc-editor.org/rfc/rfc4291 - Defines the structure/architecture of IPv6 addressing, including the 128-bit address length. ↩

Address Length Comparison (IPv4 vs IPv6)

Core size of the address field in bits.

Quick Facts & Clarifications

Knowledge Check

Question 1 of 3
Q1Single choice

The length of an IPv6 address is:

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