IPv6 CIDR to Range
Expand an IPv6 CIDR block like 2001:db8::/48 into its first and last address and an exact address count, computed with 128-bit precision in your browser.
IPv6 CIDR to address range
Enter an IPv6 network in CIDR form to see its first and last address and the exact number of addresses it contains - computed with 128-bit BigInt arithmetic in your browser.
About IPv6 CIDR to Range
IPv6 CIDR notation writes a network as an address, a slash, and a prefix length from 0 to 128 - for example 2001:db8:abcd::/48. The prefix is the number of leading bits that stay fixed across the whole block; the remaining 128 minus prefix bits are host bits that vary. This tool turns that shorthand into the concrete boundaries of the network: the first address (the network base), the last address, and the total number of addresses the block holds.
If you paste an address that already has host bits set - a specific interface address rather than the network base - the tool masks those bits off and shows the true network address the prefix defines. Each boundary is given in both compressed RFC 5952 form and fully expanded 32-digit form, so you can copy whichever notation your firewall, router, or documentation expects.
Because IPv6 blocks are astronomically large, the address count is shown as a power of two next to a fully written-out figure with digit separators. A /64 holds 2^64 = 18,446,744,073,709,551,616 addresses. For any prefix of /64 or shorter the tool also reports how many /64 subnets fit inside, which is useful because the /64 is the standard subnet size for a single LAN and address plans are usually laid out in /64 units - a /48 site, for instance, contains 65,536 /64 subnets.
All arithmetic uses native 128-bit BigInt math and runs entirely in your browser, so nothing you type is sent to a server. That makes the tool safe for planning internal or not-yet-public address space, and as a self-hosted European service the page loads no third-party scripts or trackers.
How to use it
- 1Enter an IPv6 network in CIDR form, such as 2001:db8:abcd::/48, in the input field.
- 2Let the tool parse the address and prefix as you type; it validates that the prefix is an integer from 0 to 128.
- 3Read the first and last addresses, each shown in both compressed and expanded notation.
- 4Check the total address count and, for a /64 or shorter prefix, the number of /64 subnets the block contains.
- 5Use the copy button on any row to drop the value straight into a firewall rule, route, or IPAM record.
Common use cases
- -Documenting the exact first and last address of an allocation for an IPAM system or network diagram.
- -Writing firewall or ACL rules that need explicit range boundaries rather than CIDR shorthand.
- -Verifying how many /64 subnets a /48 or /56 allocation gives you before carving it up.
- -Teaching or learning how IPv6 prefix lengths map to address counts and subnet boundaries.
- -Confirming the network base when someone hands you a host address with an attached prefix.
Frequently asked questions
- How do I find the first and last address of an IPv6 subnet?
- Enter the subnet in CIDR notation, for example 2001:db8::/64. The first address is the network base (all host bits zero) and the last address has every host bit set to one. This tool computes both instantly and shows them in compressed and expanded form.
- How many addresses are in an IPv6 /64?
- An IPv6 /64 contains 2^64 addresses, which is 18,446,744,073,709,551,616. The /64 is the standard size for a single LAN, so every host on that link shares the same 64-bit prefix.
- What does the prefix length in an IPv6 CIDR mean?
- The prefix length is the count of leading bits that identify the network and stay constant across the block. In 2001:db8::/48 the first 48 bits are the network portion, leaving 80 host bits, so the block spans 2^80 addresses.
- What happens if I enter host bits with the prefix?
- The tool masks off any bits below the prefix length and returns the true network address. So 2001:db8::5/48 and 2001:db8::/48 produce the same first address, because the /48 boundary ignores the lower bits.
- How many /64 subnets are in a /48 or /56?
- A /48 contains 65,536 /64 subnets (2^16) and a /56 contains 256 /64 subnets (2^8). This tool reports the exact /64 count for any prefix of /64 or shorter.
- Is my IPv6 input sent to a server?
- No. The conversion runs entirely in your browser using 128-bit BigInt arithmetic, so the address you enter never leaves your device. That keeps internal or unannounced address plans private.