What is the size of an IPv6 address (in bits)?
2024
What is the size of an IPv6 address (in bits)?
Answer: C. 128 bits — ConceptAn IP address is a fixed-length binary identifier. IPv6 was introduced to greatly expand the limited address space of IPv4, so it defines a longer…
- A.
32 bits
- B.
64 bits
- C.
128 bits
- D.
256 bits
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Show answer & explanation
Correct answer: C
Concept
An IP address is a fixed-length binary identifier. IPv6 was introduced to greatly expand the limited address space of IPv4, so it defines a longer fixed-length address whose size is standardised by RFC 4291.
Applying it here
RFC 4291 fixes the length of every IPv6 address at 128 bits. This length is organised as eight 16-bit groups called hextets, so 8 × 16 = 128 bits. When fully written out, each 16-bit group becomes four hexadecimal digits, giving 8 × 4 = 32 hexadecimal digits (32 × 4 = 128 bits, a consistent cross-check). The written form can be shortened by omitting leading zeros and using :: compression, but the underlying address is always 128 bits.
Why the other values do not fit
32 bits is the length of an IPv4 address, the predecessor protocol.
64 bits is the width of the interface identifier that fills the host portion of a standard /64 IPv6 subnet.
256 bits is not used as an IP address length.
Therefore, an IPv6 address is 128 bits long.