IPv6 Subnet Calculator

Calculate IPv6 subnet ranges, prefixes, address allocation, and network details quickly with this IPv6 subnet calculator.
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Overview

The IPv6 Subnet Calculator takes an IPv6 address and a prefix length and computes the network, gateway, and last address of the subnet instantly. It recognizes the address type, shows compressed and full forms, and draws a visual bar plus a 128-bit binary breakdown. A split table lists every possible /prefix network inside the containing 16-bit boundary.

Common Use Cases

How to Use

1
Enter an IPv6 address, for example 2001:db8::1; the compressed form with :: is accepted.
2
Pick the prefix length from the dropdown; it defaults to /64 and accepts values from 0 to 128.
3
Read the badges for prefix length, detected address type, and number of host bits.
4
Check the details table for the compressed and full forms of the input, network, gateway, and last address, plus CIDR notation and total addresses.
5
Use the split table to see all /prefix networks in the containing block; your subnet is highlighted.
6
Read the info alert noting that IPv6 has no broadcast and that subnets below /64 are not recommended for standard deployments.

Example Scenario

Subnetting 2001:db8:0:1::5 with a /64 prefix

Enter 2001:db8:0:1::5 with prefix 64. The tool reports the network as 2001:db8:0:1::, the gateway as 2001:db8:0:1::1, and the last address as 2001:db8:0:1:ffff:ffff:ffff:ffff. The type badge shows Documentation (TEST-NET), and the split table lists all /64 networks inside the containing /48 block 2001:db8::.

Technical Notes

IPv6 has no broadcast address. The last address in a subnet is simply the highest host address, and the tool labels it Last Address rather than broadcast.

The gateway shown is the first usable address, calculated as the network address plus one. For a /128 prefix the network address is the only address and is used as the gateway.

The tool auto-detects common IPv6 address types: documentation ranges like 2001:db8::, link-local fe80::, unique local fc00::, multicast ff00::, loopback ::1, IPv4-mapped ::ffff:0:0/96, and transition mechanisms such as 6to4 and Teredo.

Stateless address autoconfiguration (SLAAC) requires a /64 subnet. Smaller prefixes, such as /127 or /128, are special cases used for point-to-point links and loopbacks, and the tool reminds you that subnets below /64 are not recommended for standard deployments.

For prefixes with more than 60 host bits, the total address count is astronomically large and the tool reports it as greater than 10^18 instead of printing an unreadable number. The 128-bit arithmetic uses BigInt so results stay exact.

Common Mistakes

Frequently Asked Questions

IPv6 replaced broadcast with multicast. There is no all-hosts broadcast address, so the last address of a subnet is simply the highest usable address.

Full notation writes all eight 16-bit groups with leading zeros. Compressed notation removes leading zeros and replaces the longest run of zero groups with ::. Both describe the same address.

SLAAC, the standard IPv6 address autoconfiguration, generates host identifiers from a 64-bit interface ID and therefore requires a /64 prefix. Smaller prefixes are only used in special cases such as point-to-point links.

The calculator inspects the leading bits of the address and labels it, for example link-local for fe80::, unique local for fc00::, multicast for ff00::, or global unicast when no special pattern matches.

Related Topics

IPv4 Subnet CalculatorIPv4 IPv6 ConverterSLAAC6to4Teredo