IPv6 Subnet Calculator
Calculate how many hosts and subnets fit in an IPv6 prefix (/n). A tool for network administrators planning IPv6 addressing.
Hosts/Sub-redes
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How IPv6 subnetting works
Where IPv4 had 32 bits, IPv6 works with 128-bit addresses, which works out to 2¹²⁸ ≈ 3.4 × 10³⁸ unique addresses. You write one as 8 groups of 4 hexadecimal digits joined by colons (say, 2001:0db8:85a3:0000:0000:8a2e:0370:7334), and the :: shorthand collapses one run of consecutive zero groups down to nothing (2001:db8::1). The prefix tells you how many bits belong to the network. A /64 is the standard for any LAN, giving 2⁶⁴ ≈ 18.4 quintillion hosts per subnet and making SLAAC possible. A /48 is allocated per customer site, which is 65,536 /64 subnets, while a /56 is common in residential broadband. The host count in a prefix /n is 2^(128−n), and the number of /64 subnets inside a /n is 2^(64−n). So a /48 holds 2⁽⁶⁴⁻⁴⁸⁾ = 65,536 /64 subnets. RFC 4291 reserves the 2000::/3 range for global addressing.
Applications
ISPs lean on this when they plan customer allocation, delegating a /56 or /48 over DHCPv6-PD. Datacenters use it to segment VLANs across /64 racks. In IoT, every device can take a unique global address with no NAT in the way. Corporate networks route between sites with a /48 per location. It also covers ARIN, RIPE and LACNIC allocations, staying compliant with RFC 4291 and RFC 6177, and migrating off IPv4 using dual stack.
FAQ
Why is /64 the standard for LAN? SLAAC (RFC 4862) and EUI-64 build host addresses from the MAC using the lower 64 bits. Carve a subnet smaller than /64 and SLAAC stops working.
Are there reserved or unusable addresses inside the subnet? Basically none. IPv6 dropped broadcast and never adopted IPv4's host-bits convention. There's the all-zeros address (subnet-router anycast) and a handful of special suffixes, but they don't really dent your host capacity.
How much does a typical home receive? Most residential broadband subscribers are handed a /56 or /60 through DHCPv6 Prefix Delegation. That's room for 256 or 16 internal /64 subnets, respectively.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.