IPv6 Subnet Calculator
Network address, last address, total and usable address counts for any IPv6 prefix, with /127 point-to-point and /128 host-route handling, reverse-DNS zone and classification.
Input
Mode
Accepts 2001:db8::1/64, 2001:db8::1 64, or a bare address (assumed /64).
Summary
- Network
- 2001:db8:abcd:12::/64
- Last address
- 2001:db8:abcd:12:ffff:ffff:ffff:ffff
- Total addresses
- 18446744073709551616
- Readable size
- 16 Ei
- Usable addresses
- 18446744073709551614
- Prefix length
- /64
2^64 = 18,446,744,073,709,551,616
2^64 addresses
Excluding the subnet-router anycast address
64 host bits
Block geometry
- Address as typed
- 2001:db8:abcd:12::5
- Network address
- 2001:db8:abcd:12::
- Last address
- 2001:db8:abcd:12:ffff:ffff:ffff:ffff
- Usable range
- 2001:db8:abcd:12::1 – 2001:db8:abcd:12:ffff:ffff:ffff:fffe
- Addresses in block (exact)
- 18446744073709551616
Input: 2001:db8:abcd:12::5
2^64 = 18,446,744,073,709,551,616
Offset 5 from the network address
Classification and reverse DNS
- Scope
- Documentation (RFC 3849)
- Reverse DNS name
- 5.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.2.1.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa
- Delegatable reverse zone
- 2.1.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa
Nibble-reversed, under ip6.arpa (RFC 3596 §2.5)
ip6.arpa delegation happens on nibble boundaries
Representations
The same 128 bits in every notation
- RFC 5952 canonical
- 2001:db8:abcd:12::5
- Fully expanded
- 2001:0db8:abcd:0012:0000:0000:0000:0005
- Hex groups
- 2001:0db8:abcd:0012:0000:0000:0000:0005
- 128-bit integer
- 42540766464452359661416384011178082309
Exact — a double cannot hold this
Binary, grouped by hextet
0010000000000001 0000110110111000 1010101111001101 0000000000010010 0000000000000000 0000000000000000 0000000000000000 0000000000000101
Frequently asked
- Are there network and broadcast addresses in IPv6?
- There is no broadcast address in IPv6, so a traditional reserved pair does not exist. The all-zeros subnet-router anycast address is reserved by convention, which is why this calculator shows a /64 as 18,446,744,073,709,551,614 usable addresses rather than 2^64.
- Why does a /127 show two usable addresses?
- RFC 6164 allows both addresses of a /127 to be used on an inter-router link, which removes the old advice to number point-to-point links out of a /64. The calculator applies RFC 6164 by default and can show the legacy reading instead.
- How many addresses are in a /64?
- A /64 contains exactly 2^64 addresses, which is 18,446,744,073,709,551,616. That is 16 EiB in binary units. No floating-point arithmetic can hold that number exactly, so the count is computed with 128-bit integers.
- What is the ip6.arpa zone for a prefix?
- Reverse DNS for IPv6 lives under ip6.arpa and is delegated on nibble, or 4-bit, boundaries. A 2001:db8::/32 prefix delegates 8.b.d.0.1.0.0.2.ip6.arpa. Only nibble-aligned prefixes can be delegated, so a /33 keeps the /32 zone.
- Is my address sent anywhere?
- No. Every calculation runs in your browser and the page makes no network requests at all.
Next
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