IPv6 /40 Subnet
A /40 holds 16,777,216 /64 networks. Enter any address below to see its /40 block.
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Examples:
IPv6 network
16,777,216 /64 networks
Documentation
Details
First Address
Last Address
Total Addresses
/64 Networks
Expanded
Address Entered
Split Into Subnets
2001:db8:ab00::/412001:db8:ab00:: – 2001:db8:ab7f:ffff:ffff:ffff:ffff:ffff
2001:db8:ab80::/412001:db8:ab80:: – 2001:db8:abff:ffff:ffff:ffff:ffff:ffff
Subnet Calculator
IPv6 /40 at a glance
Prefix/40
Total Addresses2^88
/64 Networks16,777,216
/48 Sites256
/56 Customers65,536
Host Bits88
Hex Digits Fixed10
An IPv6 /40 fixes the first 40 of 128 bits. That is exactly 10 hex digits, so the boundary falls cleanly between digits, which makes addresses easy to read.
IPv6 has no broadcast address, so every address in the block can be used, but networks with hosts on them should be /64 so SLAAC and neighbour discovery work as designed.
Questions
How many /64s are in a /40?
16,777,216.
How many addresses are in an IPv6 /40?
2^88 (3.09 × 10^26).
What size IPv6 block should a hosting provider give each VM?
A /64 per VM is the cleanest: the customer can use any addresses inside it, and abuse handling and reverse DNS work per /64. A single /128 also works but some software expects a /64.
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