Compression follows RFC 5952. IPv4 subnet calculator →
IPv6 — common questions
How is IPv6 different from IPv4?
IPv6 addresses are 128 bits (vs 32 for IPv4), written as eight groups of four hex digits, e.g. 2001:db8::1. There’s no broadcast address and no NAT by design; a single /64 holds 18 quintillion addresses, and a typical site is allocated a /48 (65,536 /64 subnets). This calculator handles the compression, prefix maths and scope.
What is IPv6 compression (the "::")?
Per RFC 5952, leading zeros in each group are dropped and the longest run of all-zero groups is replaced once with "::". So 2001:0db8:0000:0000:0000:0000:0000:0001 compresses to 2001:db8::1. The calculator shows both the compressed and fully-expanded forms.
What is a /64 and why does it matter?
The /64 is the standard IPv6 subnet size — the last 64 bits are the interface identifier, which SLAAC and many features assume. You subnet within your site allocation (e.g. a /48) by handing out /64s. The calculator shows how many /64s a given prefix contains.
What are ULA and link-local addresses?
fc00::/7 (usually fd00::/8) are Unique Local Addresses — IPv6’s private ranges (RFC 4193). fe80::/10 are link-local, used on a single link (RFC 4291). 2001:db8::/32 is reserved for documentation (RFC 3849). The calculator flags the scope automatically.