IPv6 Address Calculator

IPv6 Prefix & Interface ID Calculator

Calculate the network prefix and interface portion of an IPv6 address for any prefix length from /0 to /128. View the expanded address, compressed address, network address, prefix mask, host-bit count and subnet boundaries.

✓ IPv6 Prefix ✓ Interface ID ✓ /64 Support ✓ Network Range ✓ Binary Split

IPv6

Prefix / Interface Calculator

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IPv6 Address Compressed and fully expanded IPv6 notation are accepted.

Prefix Length Valid IPv6 prefix lengths range from /0 through /128.

Important: IPv6 addresses are 128 bits long. A /64 prefix leaves 64 bits after the network prefix, which is the common IPv6 subnet boundary. For non-/64 prefixes, this calculator reports the remaining address bits as the host/interface portion; that does not imply every IPv6 mechanism treats those bits as a conventional 64-bit Interface Identifier.

IPv6 Prefix & Interface ID Result Calculated

IPv6 Network / Prefix —

Compressed Address—

Expanded Address—

Prefix Length—

Host / Interface Bits—

Prefix Mask—

Interface / Host Value—

First Address—

Last Address—

128-Bit Address Split

Prefix

Interface / Host

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Calculation Breakdown —

What Is an IPv6 Prefix & Interface ID Calculator?

An IPv6 Prefix & Interface ID Calculator separates a 128-bit IPv6 address according to its prefix length. The prefix identifies the network portion selected by the CIDR prefix, while the remaining bits form the portion available after that prefix.

For a conventional /64 IPv6 subnet, the first 64 bits are the subnet prefix and the remaining 64 bits occupy the Interface Identifier portion of the address. The calculator also supports arbitrary prefix lengths such as /48, /56, /60, /96 and /128.

How an IPv6 Address Is Split

IPv6 contains exactly 128 address bits. The basic calculation is:

Prefix bits = prefix length

Remaining bits = 128 - prefix length

Example /64:

128 - 64 = 64 remaining bits

The network address is calculated by preserving the prefix bits and clearing every bit after the prefix to zero.

IPv6 /64 Prefix Example

Address:
2001:db8:1234:5678:abcd:ef01:2345:6789

Prefix:
/64

Network prefix:
2001:db8:1234:5678::/64

Remaining 64-bit value:
abcd:ef01:2345:6789

Because /64 falls exactly on a four-hextet boundary, the split is especially easy to see.

IPv6 Prefix Length Table

Prefix	Network Bits	Remaining Bits	Typical Interpretation
/32	32	96	Large routed prefix allocation boundary in some deployment contexts
/48	48	80	Common site-prefix size
/56	56	72	Common delegated-prefix size
/64	64	64	Standard IPv6 subnet boundary for many networks
/96	96	32	32 address bits remain after the prefix
/128	128	0	One exact IPv6 address

What Is an IPv6 Interface Identifier?

In the familiar /64 IPv6 addressing model, the Interface Identifier occupies the low-order 64 bits of the IPv6 address. It may be created using several address-generation mechanisms rather than necessarily being derived from a hardware MAC address.

For this reason, seeing a 64-bit Interface Identifier does not automatically mean the address contains an EUI-64 encoded MAC address.

IPv6 Prefix Mask Calculation

A prefix mask contains one bits for the selected network prefix followed by zero bits for the remaining portion.

/64 mask:

ffff:ffff:ffff:ffff:0000:0000:0000:0000

Compressed:
ffff:ffff:ffff:ffff::

Example of a Prefix That Does Not End on a Hextet

IPv6 CIDR prefixes do not have to end on a 16-bit hextet boundary. For example, a /60 prefix ends four bits into the fourth 16-bit hextet.

Prefix length = /60

Network bits = 60
Remaining bits = 68

The calculator performs the split at the bit level,
not merely between colon-separated hextets.

IPv6 First and Last Address

For the mathematical CIDR range represented by an IPv6 prefix, the first address has all bits after the prefix cleared to zero. The last address has all remaining bits set to one.

Unlike IPv4 subnet calculations, do not automatically treat the first and last IPv6 addresses as traditional network and broadcast reservations. IPv6 does not use IPv4-style broadcast addressing.

Compressed vs Expanded IPv6 Address

An expanded IPv6 address always contains eight groups of four hexadecimal digits. Compressed notation can remove leading zeros and replace one contiguous run of zero hextets with ::.

Expanded:
2001:0db8:0000:0000:0000:0000:0000:0001

Compressed:
2001:db8::1

IPv6 Prefix Calculator FAQs

How many bits are in an IPv6 address?

An IPv6 address contains 128 bits.

What does /64 mean in IPv6?

It means the first 64 bits are selected by the network prefix, leaving 64 address bits after the prefix.

What is the Interface ID in an IPv6 /64?

For a conventional /64 subnet, the Interface Identifier occupies the low-order 64 bits.

Does every IPv6 Interface ID come from a MAC address?

No. Modern IPv6 systems can generate interface identifiers using several methods, including stable or temporary privacy-oriented mechanisms.

Can IPv6 use prefix lengths other than /64?

Yes. IPv6 CIDR permits prefix lengths from /0 through /128, although particular protocols and network designs can impose additional requirements.

What does /128 mean?

A /128 prefix identifies one exact 128-bit IPv6 address and leaves no host bits after the prefix.

Does IPv6 have a broadcast address?

No. IPv6 does not use IPv4-style broadcast addresses. Multicast is used for functions that would traditionally involve broadcast.

Can the calculator handle compressed IPv6 addresses?

Yes. Addresses such as 2001:db8::1 and ::1 are expanded internally before the prefix calculations are performed.

What is an IPv6 prefix mask?

It is a 128-bit mask containing ones for the prefix bits and zeros for all bits after the selected prefix.

Can a prefix split occur inside a hextet?

Yes. Prefixes such as /53 or /60 do not align exactly with 16-bit colon-separated hextet boundaries, so they must be calculated at bit level.

Calculate IPv6 Prefixes and Interface Bits

Enter an IPv6 address and CIDR prefix length to inspect its normalized address, network prefix, remaining interface or host bits, prefix mask and complete mathematical address range.