IPv6 calculator
Paste an IPv6 address, with or without a prefix. It is shown in both its short and full forms, split into the part the network chose and the part the device chose, and — given a prefix — worked out as a range.
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Reading an IPv6 address
An address is 128 bits, written as eight groups of four hex digits separated by colons. Two shortcuts make it readable: leading zeros in a group are dropped, and the longest run of all-zero groups is replaced by ::, once. So 2001:0db8:0000:0000:0000:0000:0000:0001 is written 2001:db8::1.
The two halves
The first 64 bits locate the network: a routing prefix from the provider followed by a subnet number. The last 64 bits, the interface ID, identify the device on that network and are usually chosen by the device itself.
Common prefix sizes
- /128 — a single address.
- /64 — one network. The normal size of a LAN.
- /56 — a common home allocation: 256 networks.
- /48 — a common site allocation: 65,536 networks.
- /32 — a common allocation to an internet provider.
Why are IPv6 addresses so long?
They are 128 bits against IPv4’s 32, which is written as eight groups of four hexadecimal digits. The length is the point: there are enough addresses that every device can have a globally unique one without NAT.
What does :: mean?
It stands in for one run of consecutive all-zero groups. It may appear only once in an address, otherwise it would be ambiguous how many zeros each one replaced.
Why is /64 everywhere?
It is the standard size for a single network. Automatic address configuration (SLAAC) needs a 64-bit interface ID, so a LAN is almost always a /64 and allocations are counted in how many /64s they contain.
Should I worry about an EUI-64 address?
It is a privacy concern rather than a security one: the interface ID is derived from the network card, so the same device can be recognised across networks. Current Windows, macOS, iOS and Android use randomised addresses for outgoing connections by default.
Is the address I type sent anywhere?
No. Every calculation happens in your browser, and no request is made when you press Calculate.