What is the :: shorthand in IPv6?

The double-colon (::) represents one or more consecutive groups of 16 bits that are all zeros. It may appear only once in an address. For example, 2001:db8::1 expands to 2001:0db8:0000:0000:0000:0000:0000:0001.

How many addresses does a /48 prefix contain?

A /48 subnet contains 2^(128-48) = 2^80 addresses, which is approximately 1.2 × 10^24. IPv6 subnets are intentionally very large to support hierarchical routing and address auto-configuration.

What is the difference between network address and first host in IPv6?

Unlike IPv4, IPv6 does not reserve a separate broadcast address. The network address (all host bits zero) is the subnet identifier, and the very next address (host bits = 1) is the first usable host. The last address (all host bits one) is technically usable but is often treated as the subnet-router anycast address on /64 subnets.

What prefix length should I use for end-user LANs?

The standard recommendation (RFC 6177) is to assign /64 prefixes to end-user LAN segments. This allows Stateless Address Autoconfiguration (SLAAC) to work correctly and provides 2^64 host addresses per segment.

Does this tool support IPv4-mapped IPv6 addresses?

The tool handles standard IPv6 addresses including the :: shorthand. IPv4-mapped addresses (::ffff:192.0.2.1) are parsed as regular IPv6 addresses; the IPv4 embedded portion is not extracted separately.

Why is total addresses shown as a power of 2?

IPv6 subnets can be astronomically large. A /1 subnet contains 2^127 addresses — a number with 38 digits. Displaying the value as 2^N keeps it readable and avoids integer overflow in JavaScript. For small subnets (/120 and smaller) the exact decimal count is also shown.

IPv6 Subnet Calculator

Name: IPv6 Subnet Calculator
Availability: InStock
Author: Nham Vu

Enter an IPv6 address with prefix length (e.g. 2001:db8::1/48) to get the network address, host range, total addresses, and both expanded and compressed notations.

IPv6 Address & Prefix

IPv6 Address / CIDR

Enter address with prefix, e.g. 2001:db8::1/48

Prefix Length (0–128)

Optional — overrides any prefix in the address field.

Quick examples

Enter an IPv6 address with prefix length and click Calculate.

Address Notation

Input

Expanded

Compressed

Prefix Length

Subnet Details

Network Address

First Address

Last Address

Total Addresses

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Summary

Enter an IPv6 address with prefix length (e.g. 2001:db8::1/48) to get the network address, host range, total addresses, and both expanded and compressed notations.

How it works

Enter an IPv6 address with its prefix length in CIDR notation (e.g. 2001:db8::1/48).
The tool expands the address to its full 128-bit form, resolving any :: shorthand.
It masks the address with the prefix length to derive the network address.
The last address is found by setting all host bits to 1.
Total addresses in the subnet are calculated as 2^(128 - prefix).
Results are displayed in both expanded (full) and compressed (RFC 5952) notation.

Use cases

Plan IPv6 address allocation for enterprise or ISP networks.
Verify IPv6 subnetting for CCNA/CCNP exam practice.
Design cloud VPC or data-center IPv6 CIDR blocks.
Convert between expanded and compressed IPv6 notations.
Determine the network address and host range of an IPv6 subnet.
Check whether two IPv6 addresses belong to the same subnet.
Document IPv6 topology with accurate subnet parameters.
Troubleshoot routing issues by confirming IPv6 network boundaries.

Frequently Asked Questions

Last updated: 2026-06-10 · Reviewed by Nham Vu