IPv6 Calculator

To calculate an IPv6 subnet range, enter the IPv6 address with its prefix length, such as 2001:db8:100:20::1/64. The calculator normalizes the address, identifies the prefix bits, and shows the first and last address in that subnet. It can also show the address count, which is often enormous compared with IPv4. Remember that IPv6 has no broadcast address. The last address is only the end of the range. This helps with route planning, firewall rules, IPAM entries, and understanding delegated prefixes.

An IPv6 /64 contains 2^64 addresses, which is 18,446,744,073,709,551,616 addresses. That number surprises many students coming from IPv4. A /64 is common on LAN segments because IPv6 addressing and neighbor discovery were designed around that size for many use cases. It does not mean you should try to count or scan all hosts in a /64. In IPv6, subnet size is often about design, autoconfiguration, and routing structure, not about squeezing every possible address into use.

To expand a compressed IPv6 address, replace the :: with enough zero groups to make eight 16-bit groups. For example, 2001:db8::1 expands to 2001:0db8:0000:0000:0000:0000:0000:0001. Each group is hexadecimal and can contain leading zeros when fully expanded. Only one :: can appear in a valid IPv6 address because the device must know how many zero groups were omitted. Expansion is useful when comparing prefixes, reading logs, or teaching how the 128-bit address is actually structured.

The first address in an IPv6 prefix is the prefix with all host bits set to zero. The last address is the same prefix with all host bits set to one. For 2001:db8:10::/64, the range starts at 2001:db8:10:: and ends at 2001:db8:10:0:ffff:ffff:ffff:ffff. Unlike IPv4, the last address is not a broadcast address because IPv6 does not use broadcast. You still may reserve certain addresses by design, such as router addresses, but that is an operational choice.

No, IPv6 does not have a broadcast address. IPv4 uses broadcast to send traffic to all hosts in a subnet, but IPv6 uses multicast and neighbor discovery instead. For example, IPv6 has multicast groups for all nodes and solicited-node neighbor discovery. This difference is important when students expect a /64 to have a network and broadcast address like IPv4. The first address is the subnet-router anycast address in some contexts, and the last address is just the end of the range, not broadcast.

Common IPv6 prefix lengths depend on the design. A /64 is commonly used for a single LAN or VLAN. A /56 is often used to give a site or customer enough room for many /64s. A /48 is commonly seen as a larger site or enterprise allocation. These are design conventions, not magic values that fit every network. The important habit is to plan hierarchically: allocate a larger parent prefix, break it into site or function blocks, then assign /64s where hosts live.

To check whether an IPv6 address is link-local, see whether it falls inside fe80::/10. Link-local addresses are used only on the local link and are not routed across the internet. You will often see them on interfaces automatically, and they are used by neighbor discovery and routing protocols. In output, a link-local address may include a zone index, such as %eth0, to identify the interface. Do not use a link-local address as if it were a global address reachable from anywhere.