Network · Subnetting
IPv6 Subnet Calculator
Calculate IPv6 prefixes, address ranges and subnets, and expand or compress any IPv6 address.
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Network Engineering
IPv6 Subnet
Calculator
Calculator
The most complete IPv6 subnet tool. Expand compressed addresses, calculate network prefixes, split subnets, visualise 128-bit binary maps, detect address types and scopes, and convert between all formats instantly.
Expand & compress any IPv6 address (RFC 5952)
Network address, first & last host, prefix range
128-bit binary map with network/host bit highlighting
Address type: Unicast, Multicast, Link-Local, ULA & more
Split any /prefix into N equal subnets
EUI-64 interface ID extraction & IPv4-mapped detection
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IPv6 Address Input
Accepts compressed or full notation
⚠ Invalid IPv6 address or prefix length. Example: 2001:db8::/32
Quick:
Network Details
128-bit Binary Visualisation
Address Type & Scope
Address Properties
Subnet Splitter
Split into equal subnets
| # | Network Prefix | First Address | Last Address | Prefix Len | Addresses |
|---|
Common IPv6 Prefix Lengths
| Prefix | Addresses | Common Use |
|---|
IPv6 Special Address Ranges
| Range | Type | Purpose |
|---|---|---|
| ::1/128 | Loopback | Localhost (RFC 4291) |
| ::/128 | Unspecified | Unspecified address |
| fe80::/10 | Link-Local | Auto-configured, non-routable |
| fc00::/7 | ULA | Unique Local (RFC 4193) |
| fd00::/8 | ULA | Locally assigned ULA |
| ff00::/8 | Multicast | All multicast groups |
| ff02::1 | Multicast | All nodes (link-local) |
| ff02::2 | Multicast | All routers (link-local) |
| 2001:db8::/32 | Docs | Documentation / examples |
| 2001::/32 | Teredo | Teredo tunneling (RFC 4380) |
| 2002::/16 | 6to4 | 6to4 relay (RFC 3056) |
| ::ffff:0:0/96 | IPv4-mapped | IPv4-mapped IPv6 (RFC 4291) |
| 64:ff9b::/96 | NAT64 | IPv4/IPv6 translation (RFC 6052) |
| 100::/64 | Discard | Discard prefix (RFC 6666) |
IPv6 Addressing Reference Guide
IPv6 is the next-generation Internet Protocol using 128-bit addresses, providing approximately 3.4 × 10³⁸ unique addresses. Understanding IPv6 notation, address types, and prefix allocation is essential for modern network engineers. IPv6 eliminates the need for NAT, simplifies routing, and includes built-in features like stateless address auto-configuration (SLAAC) and IPsec support.
How does IPv6 address compression work?
IPv6 addresses can be compressed in two ways: (1) leading zeros in each 16-bit group can be omitted (0042 → 42), and (2) one consecutive sequence of all-zero groups can be replaced with :: (double colon). For example, 2001:0db8:0000:0000:0000:0000:0000:0001 compresses to 2001:db8::1. The :: can only appear once per address (RFC 5952).
What is an IPv6 prefix and how is it different from an IPv4 subnet mask?
An IPv6 prefix works like CIDR notation in IPv4 — /64 means the first 64 bits identify the network, and the remaining 64 bits are the interface identifier (host portion). Unlike IPv4, IPv6 does not use dotted-decimal subnet masks. The most common prefix lengths are /48 for site prefixes, /64 for LAN segments, and /128 for host routes. ISPs typically assign /48 or /56 to customers.
What is a Unique Local Address (ULA) in IPv6?
Unique Local Addresses (fc00::/7, RFC 4193) are the IPv6 equivalent of RFC 1918 private addresses in IPv4. They are not globally routable but are unique enough for internal use across multiple sites. The fd00::/8 range is for locally assigned ULAs — the L bit is set and a 40-bit random Global ID should be generated to minimise collision probability when merging networks.
What is SLAAC and how does it use the /64 prefix?
Stateless Address Autoconfiguration (SLAAC, RFC 4862) allows IPv6 hosts to automatically configure their own address without DHCP. The router advertises a /64 network prefix, and the host combines it with a 64-bit Interface Identifier (derived from the MAC address via EUI-64 or a random value via RFC 7217 privacy extensions). This is why /64 is the standard LAN prefix — splitting it would break SLAAC.
What are link-local addresses and when are they used?
Link-local addresses (fe80::/10) are automatically assigned to every IPv6 interface and are only valid on the local network segment — they cannot be routed. They are used for neighbor discovery (NDP), router discovery, and as next-hop addresses in routing protocols like OSPFv3 and EIGRP for IPv6. You must specify the interface (e.g., fe80::1%eth0) when connecting to a link-local address.
How many addresses does an IPv6 /64 subnet contain?
A /64 subnet contains 2^64 = 18,446,744,073,709,551,616 addresses (about 18.4 quintillion). A /48 site prefix contains 2^80 ≈ 1.2 × 10²⁴ addresses and can be divided into 65,536 /64 subnets. A /32 (typical ISP allocation) contains 2^96 addresses and supports 65,536 /48 sites. The entire IPv4 internet fits into a tiny fraction of the IPv6 address space.
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