Enter the prefix you were given and the size of the pieces you need. Get every subnet with its range — for carving a /48 into sites, or a /56 into /64 networks.
Runs entirely in your browser — nothing you enter here is sent to a server.
IPv6 planning is about counting networks, not hosts. A single /64 holds more addresses than any LAN will ever use, so the question is only how many /64s you need and how to group them. An ISP hands a site a /48 or a /56; you split that into blocks for locations, security zones or environments, and each block into /64 networks.
Prefix lengths divisible by four (/48, /52, /56, /60, /64) line up with the written digits, so subnets are readable at a glance.
Autoconfiguration needs it. Do not try to save space with /80 or /112 networks.
Assign every second or fourth block, so that a site can grow into the neighbouring one.
Router-to-router links take a /127 (RFC 6164), usually carved from one reserved /64.
You receive 2001:db8:abcd::/48. Splitting it into /56s gives 256 blocks — 2001:db8:abcd:0000::/56, 2001:db8:abcd:0100::/56 and so on — one per building or environment. Each /56 then holds 256 /64 networks: …:0100::/64 for servers, …:0101::/64 for staff, …:0102::/64 for guests. The fourth group of the address now reads as "site, then network", and a firewall rule for a whole building is one /56.
256. Eight bits separate the two prefix lengths. A /48 contains 65,536 /64s, and a /60 contains 16.
Each hexadecimal digit is four bits. A /52 ends exactly after a digit, so each subnet differs from the next in one visible character. A /53 splits a digit in half and is much harder to read.
Only for special cases: /127 on point-to-point links and /128 for a single address such as a loopback. Ordinary networks should be /64.
The table shows the first 256 and tells you the total and the last one. The totals above it are exact.
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