Enter a prefix like 2001:db8::/48 to see the range it covers, or two addresses to get the shortest list of CIDR blocks for exactly that range.
Runs entirely in your browser — nothing you enter here is sent to a server.
IPv6 uses the same slash notation as IPv4, with 128 bits instead of 32. 2001:db8:abcd::/48 fixes the first 48 bits and leaves 80 free — 2⁸⁰ addresses. There are no netmasks written out in IPv6 and no broadcast address; every address in a prefix can be assigned.
The standard size of a single LAN or VLAN. Automatic addressing (SLAAC) needs exactly 64 host bits.
256 networks of /64. A common allocation from ISPs to residential customers.
65,536 networks of /64. The usual assignment to a business location.
The typical minimum allocation to an ISP or hosting company: 65,536 /48 sites.
Routers, firewalls and cloud security groups take IPv6 prefixes, not ranges. When you are handed a range — in a vendor's documentation, or from a whois record — convert it to blocks before writing a rule. Ranges that begin and end on prefix boundaries collapse into a single block; anything else needs several, each starting on a multiple of its own size. The list here is the shortest exact cover.
When you filter by address, remember that one visitor usually holds a whole /64 and may change the last 64 bits every day through privacy extensions. Rate limits, bans and allowlists for end users are normally applied to the /64, not to the single /128.
18,446,744,073,709,551,616 — 2⁶⁴. That is the size of one ordinary IPv6 network, however few devices are on it.
No. IPv6 has no broadcast, and the first address of a prefix is the subnet-router anycast address rather than an unusable one. In practice every address can be used.
Stateless address autoconfiguration, privacy addresses and several other mechanisms assume a 64-bit interface identifier. Longer prefixes are used only for point-to-point links (/127) and loopbacks (/128).
65,536. There are 16 bits between the two prefix lengths, and 2¹⁶ = 65,536.
Upzilla checks your services from outside and alerts you when they stop answering. 10 monitors free.