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IPv6 Subnet Calculator

DeveloperNetworking

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INPUT

Auto Process

OUTPUT

Client Side

Property	Value
Network Address	-
Network (Compressed)	-
Prefix Length	-
Subnet Mask (Expanded)	-
First Usable Address	-
Last Usable Address	-
Total Addresses	-
Expanded Address	-
Compressed Address	-
Reverse DNS (ip6.arpa)	-
Binary	-

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Guide

IPv6 Subnet Calculator

Calculate IPv6 subnet details from a CIDR notation address. Enter any IPv6 address with a prefix length (e.g. 2001:db8::1/48) and instantly see the network address, first and last usable host, subnet mask, total address count, address type classification, and full expanded/compressed forms.

How to Use

Enter an IPv6 address with its prefix length in CIDR notation (e.g. 2001:db8::/32 or fe80::1/64) and click Calculate. All subnet details appear instantly including the network address, host range, and address count.

Features

Full subnet breakdown – network address, first/last host, prefix mask
Address count – total addresses in the subnet (displayed for all prefix lengths)
Address type detection – identifies global unicast, link-local, loopback, multicast, and more
Expanded and compressed forms – shows both full and compressed IPv6 representations
CIDR input – accepts any prefix length from /0 to /128
Client-side only – no data sent to servers

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 FAQ

How does IPv6 subnetting differ from IPv4?

IPv6 uses 128-bit addresses vs IPv4’s 32 bits, making the address space 2⁹¶ times larger. IPv6 subnetting follows the same CIDR principles but the numbers are vastly different: a /48 prefix (standard for a site) contains 2⁸⁰ addresses — more than the entire IPv4 internet. In practice, /64 is the standard subnet size for LANs because SLAAC (Stateless Address Autoconfiguration) requires a /64 for the 64-bit interface identifier.
What are the main IPv6 address types?

Global Unicast (2000::/3) — publicly routable, equivalent to public IPv4. Link-Local (fe80::/10) — auto-configured, valid only within a single link, not routed. Loopback (::1/128) — equivalent to 127.0.0.1. Multicast (ff00::/8) — one-to-many delivery. Unique Local (fc00::/7) — private use, similar to RFC 1918. Documentation (2001:db8::/32) — reserved for examples and documentation only.
Why is /64 the standard IPv6 LAN prefix size?

RFC 4291 defines the IPv6 address as a 64-bit network prefix + 64-bit interface identifier. SLAAC (RFC 4862) uses the Modified EUI-64 algorithm to derive the interface ID from the MAC address, which requires exactly 64 bits. DHCPv6 also assumes /64 subnets in most implementations. Using longer prefixes (/65 to /127) is technically valid but breaks SLAAC and some other IPv6 features.
What is the difference between expanded and compressed IPv6 notation?

Expanded notation writes all 32 hex digits: 2001:0db8:0000:0000:0000:0000:0000:0001. Compressed notation (RFC 5952) drops leading zeros in each group and replaces the longest consecutive run of all-zero groups with :: giving: 2001:db8::1. The :: can appear only once in an address. Compression is purely cosmetic — both forms represent identical binary addresses.