IPv6 Subnet Calculator
Enter any IPv6 address — compressed, expanded, or with an embedded IPv4 like ::ffff:192.168.1.1 — and pick a prefix length from /0 to /128. Get the full subnet breakdown instantly: expanded and compressed forms, network and last address, total address count (as a power of two and a /64 count), address type, ip6.arpa reverse DNS nibble pointer, and a subnet-split helper to list the first several sub-prefixes.
Reverse DNS (ip6.arpa)
Nibble-by-nibble pointer for the input address:
Split this prefix
Divide the network into smaller sub-prefixes:
Use — Guide
How to use this tool
- Enter any IPv6 address in the "IPv6 Address" field — compressed forms (e.g. 2001:db8::1), fully expanded forms, or embedded IPv4 addresses (e.g. ::ffff:192.168.1.10) are all accepted.
- Choose a prefix length from the "Prefix" dropdown (/0 to /128). Common allocation sizes are /48 (site), /56 (customer), /64 (LAN segment) and /128 (single host).
- Read the result grid: expanded and compressed address forms, network (prefix) address, last address, total address count (shown as 2^n), the number of /64 subnets contained, address type and CIDR notation.
- Check the "Reverse DNS (ip6.arpa)" section for the nibble-by-nibble pointer format needed to configure reverse DNS delegations.
- Use the "Split this prefix" section to list the first sub-prefixes — enter a new prefix length longer than the current one and the tool shows the resulting sub-networks.
- Click any copy icon to copy a value to the clipboard.
FAQ — Questions
Frequently asked questions
01What is a /64 prefix in IPv6?
A /64 is the standard size for an IPv6 LAN segment. With 64 network bits and 64 host bits, it contains 2^64 addresses — roughly 18.4 quintillion. ISPs typically assign a /48 or /56 to a customer site, which can then be subdivided into /64s for individual VLANs. A /64 is also required for Stateless Address Autoconfiguration (SLAAC) to function correctly.
02How does IPv6 subnetting differ from IPv4?
The fundamental principle — a prefix identifies the network, remaining bits identify hosts — is the same. The key differences are scale and convention. IPv6 addresses are 128 bits (versus 32 for IPv4), written as eight groups of four hexadecimal digits separated by colons (e.g. 2001:0db8:0000:0001::1). There are no subnet masks or wildcard masks — only prefix lengths. There is also no broadcast address; IPv6 uses multicast instead. Host addresses within a /64 are typically autoconfigured via SLAAC or DHCPv6.
03Is my data kept private?
Yes. All IPv6 subnet calculations run entirely in your browser using JavaScript and BigInt arithmetic. No addresses or prefix data are ever sent to Peritus Digital or any third party.
04Can Peritus Digital help us roll out IPv6?
Yes. IPv6 adoption requires careful planning — prefix delegation, dual-stack coexistence, firewall policy, reverse DNS and router advertisement configuration all need to work together. Peritus Digital's Newcastle team designs and manages networks for Hunter Region businesses, including IPv6 planning and dual-stack migrations. Get in touch to discuss your rollout.
More — Keep exploring
Related free tools
Want hands-on help, not just a check? Explore ourManaged IT & Support service.
Need IPv6 expertise?
From dual-stack design to IPv6 rollout — Peritus Digital can help.
Our Newcastle team designs and manages networks for Hunter Region businesses — IPv6 planning, dual-stack migrations, firewall policy, SD-WAN and structured cabling. If you're calculating prefixes, chances are you're planning infrastructure. Let's talk.