Ipv6 subnet Calculator

An IPv6 address is a 128-bit value written as eight groups of four hexadecimal digits. A prefix length such as /64 states how many leading bits identify the network; the network address is obtained by keeping those bits and forcing every remaining host bit to zero, while the last address in the block sets all host bits to one. Because the address is 128 bits wide, a block holds 2 raised to the power of (128 minus prefix) addresses, so a /64 contains 18,446,744,073,709,551,616 addresses - roughly four billion times the entire IPv4 space. Global unicast addresses live under 2000::/3, link-local addresses under fe80::/10, multicast under ff00::/8, and 2001:db8::/32 is reserved for documentation, which is why example addresses on this page begin with 2001:0db8. The /64 boundary is a design constraint, not a convention of convenience: Stateless Address Autoconfiguration and the 64-bit interface identifier both assume 64 host bits, so subnets longer than /64 break SLAAC and force DHCPv6 or static assignment. Typical allocations are a /32 to an ISP, a /48 or /56 to a site, and a /64 to each LAN segment. Two exceptions are widely used: /127 for router-to-router point-to-point links, and /128 for a single loopback or host route. IPv6 has no broadcast address, and the all-zeros interface identifier within a subnet is reserved as the subnet-router anycast address, so it should not be handed to a host. Note also that address compression using the double colon may be applied only once per address.

IPv6 grew out of the IETF response to IPv4 address exhaustion. After the ROAD group work of 1992, the IPng directorate selected a successor protocol, and Steve Deering and Robert Hinden published the first IPv6 specification as RFC 1883 in December 1995. It was revised as RFC 2460 in 1998 and finally promoted to Internet Standard as RFC 8200 in July 2017. The prefix-length notation used here was inherited from Classless Inter-Domain Routing, introduced for IPv4 in RFC 1519 in 1993, which had already replaced fixed Class A, B, and C boundaries with an explicit count of network bits. The addressing architecture itself went through several revisions: RFC 1884 in 1995, RFC 2373 in 1998, RFC 3513 in 2003, and RFC 4291 in February 2006, which remains the reference for the /64 interface identifier and the subnet-router anycast address. An early aggregation scheme in RFC 2374 divided the top bits into TLA and NLA fields; it proved too rigid and was deprecated by RFC 3587 in 2003, leaving the simpler model of a routing prefix, a subnet identifier, and a 64-bit interface identifier. Allocation policy also loosened over time: RFC 3177 recommended a /48 for essentially every end site, and RFC 6177 replaced it in 2011 with the more flexible guidance that end sites receive enough space for multiple subnets, commonly a /48 or /56.