IPv6 Subnet Calculator
How it works
Enter an IPv6 address with prefix length in CIDR notation. The calculator determines the network address, address range, total address count, and address type. All calculations use 128-bit arithmetic with BigInt.
IPv6 uses 128-bit addresses written as eight groups of four hexadecimal digits separated by colons, such as2001:0db8:0000:0000:0000:0000:0000:0001. Consecutive groups of zeros can be compressed to::once per address, giving the shorter form2001:db8::1.
IPv6 subnetting works like IPv4 CIDR but with 128 bits instead of 32. A/48prefix leaves 80 bits for the subnet and interface portions, yielding 2⁸⁰ addresses — more than the entire IPv4 address space many times over.
Unlike IPv4, there is no broadcast address in IPv6. Multicast groups replace broadcast for one-to-many delivery. SLAAC (Stateless Address Autoconfiguration) lets hosts configure their own addresses within a /64 without a DHCP server.
Common IPv6 prefix lengths
| Prefix | Purpose |
|---|---|
| /128 | Single host (loopback, specific host) |
| /127 | Point-to-point link (RFC 6164) |
| /64 | Standard subnet (required for SLAAC) |
| /48 | Typical site/organization allocation |
| /32 | Typical ISP allocation from RIR |
| /16 | Major allocations (e.g. 2002::/16 for 6to4) |
IPv6 address types
Global Unicast (2000::/3) — routable on the public internet, equivalent to IPv4 public addresses.
Link-Local (fe80::/10) — only valid on the local link, automatically assigned to every IPv6 interface.
Unique Local (fc00::/7) — private addressing for internal networks, similar to RFC 1918 in IPv4.
Multicast (ff00::/8) — one-to-many delivery; replaces IPv4 broadcast.
Loopback (::1/128) — equivalent to 127.0.0.1 in IPv4, used for localhost communication.
IPv4-Mapped (::ffff:0:0/96) — embeds an IPv4 address in the last 32 bits, e.g.::ffff:192.168.1.1. Used by dual-stack sockets to represent IPv4 peers.
FAQ
What is the standard IPv6 subnet size?
The standard IPv6 subnet size is /64. This provides 2⁶⁴ (approximately 18.4 quintillion) addresses for hosts on a single network segment. This is by convention — SLAAC (Stateless Address Autoconfiguration) requires a /64 prefix.
What is the difference between IPv4 and IPv6 subnetting?
IPv6 uses 128-bit addresses instead of 32-bit, providing a vastly larger address space. IPv6 subnetting does not use subnet masks or wildcard masks — only CIDR prefix notation. There are no broadcast addresses in IPv6; multicast replaces broadcast functionality.
What does fe80::/10 mean?
fe80::/10 is the IPv6 link-local address range. These addresses are automatically assigned to every IPv6-enabled interface and are only valid on the local network link. They are used for neighbor discovery, router solicitation, and other link-local communication.
What is an IPv4-mapped IPv6 address?
An IPv4-mapped IPv6 address has the form ::ffff:x.x.x.x (e.g., ::ffff:192.168.1.1). It allows IPv6-only applications to communicate with IPv4 hosts by embedding the IPv4 address in the last 32 bits of the IPv6 address.