IPv6 Subnet Calculator

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IPv6 subnet calculator.

Expand or compress any IPv6 address, find its prefix range and address type, split a prefix into subnets and build EUI-64 interface IDs — with ready-to-paste Cisco commands.

Prefix calculatorSubnet a prefixEUI-64 builderQuick reference

Prefix calculator

Enter an address with its prefix length, for example 2001:db8:acad:20::1/64. Compressed, expanded and IPv4-embedded forms all work.

Try:

That isn’t a valid IPv6 address. Use hex groups separated by colons, at most one “::”, and a prefix from /0 to /128.

Subnet a prefix

Split the prefix above into smaller subnets. A common plan: a /48 per site gives 65,536 /64 networks; use /64 for every LAN or VLAN so SLAAC works.

EUI-64 interface ID builder

See how a router or host turns a 48-bit MAC address into a 64-bit interface ID: split the MAC, insert FFFE in the middle and flip the 7th bit (universal/local) of the first byte.

Enter a MAC address such as 00:1A:2B:3C:4D:5E, 00-1a-2b-3c-4d-5e or 001a.2b3c.4d5e.

Privacy note: EUI-64 addresses expose the device’s MAC address. Most operating systems now use random or stable-privacy interface IDs (RFC 7217, RFC 8981) for hosts; EUI-64 remains common on router interfaces.

Quick reference

PrefixMeaningTypical use
2000::/3Global unicastInternet-routable addresses from your ISP or RIR
fc00::/7Unique local (RFC 4193); in practice fd00::/8Internal-only addressing, like RFC 1918 in IPv4
fe80::/10Link-localEvery IPv6 interface; neighbor discovery and routing-protocol next hops
ff00::/8Multicastff02::1 all nodes · ff02::2 all routers · ff02::5/6 OSPFv3 · ff02::a EIGRP
ff02::1:ff00:0/104Solicited-node multicastNeighbor discovery (replaces ARP)
2001:db8::/32, 3fff::/20Documentation (RFC 3849, RFC 9637)Examples and training — never routed
::1/128 · ::/128Loopback · unspecifiedLocal host · “no address yet”
::ffff:0:0/96IPv4-mappedDual-stack sockets showing IPv4 peers
64:ff9b::/96NAT64 well-known prefix (RFC 6052)IPv6-only clients reaching IPv4 services
/48 · /56 · /64 · /127 · /128Common lengthsSite · small site or home · one LAN · point-to-point link (RFC 6164) · loopback/host
No broadcast in IPv6. Every address in a prefix is assignable (the all-zeros interface ID is the subnet-router anycast address, so avoid giving it to hosts). Multicast replaces broadcast, and neighbor discovery replaces ARP.

🔒 Every calculation runs in your browser. Nothing you type is sent or stored. For IPv4, use the IP subnet & VLSM calculator.

⚖️ For education and use on systems you own or are authorised to test. Results are automated guidance, not a professional audit. See our terms of use and privacy policy.

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