Enter an IPv6 address and prefix to calculate the network address, host range, total address count, and 128-bit binary breakdown.
Enter an IPv6 address and prefix to calculate subnet details
An IPv6 address is 128 bits written as eight groups of four hexadecimal digits separated by colons - for example, 2001:0db8:0000:0000:0000:0000:0000:0001. Leading zeros within each group can be omitted, and one consecutive run of all-zero groups can be replaced with ::, giving the compressed form 2001:db8::1.
Like IPv4 CIDR, an IPv6 prefix is written as /N where N is the number of network bits. A /64 prefix means the first 64 bits identify the network and the remaining 64 bits identify the interface (host). The /64 boundary is by far the most common - it is the standard allocation for a single LAN segment because it enables SLAAC (Stateless Address Autoconfiguration).
/32 - typical allocation from an RIR to an ISP
/48 - standard allocation from an ISP to a customer site
/56 - sometimes given to home users by ISPs
/64 - one LAN segment (enables SLAAC)
/128 - a single interface (loopback, anycast)
Global unicast (2000::/3) - publicly routable, equivalent to IPv4 public addresses.
Link-local (fe80::/10) - automatically assigned to every interface, not routable beyond the local link. Used for neighbour discovery.
Unique local (fc00::/7) - private addresses, similar to RFC 1918. Not routable on the public internet.
Multicast (ff00::/8) - one-to-many, replaces IPv4 broadcast.
Loopback (::1/128) - equivalent to 127.0.0.1.
A /64 subnet has 64 host bits, giving 264 approximately 18.4 quintillion addresses per network segment. This is intentional - it is large enough that SLAAC can generate interface IDs randomly (or from the MAC address) with negligible collision probability, without needing DHCP assignment. The vast address space also means address scanning attacks that are trivial on IPv4 become computationally infeasible on IPv6.