IPv6 Network Calculator
Derive the IPv6 network address, prefix boundary and subnet identifier for any address and prefix length.
Inputs
Network Address
2001:db8:acad:1234::/64
Subnet ID (hex)
1234
Prefix on Nibble Boundary
Yes
Host Bits
64
Step by step
Values used
IPv6 address = 2001:db8:acad:1234:5678::1; Prefix length = 64 bits
IPv6 Network
network = address AND prefix mask, applied 16 bits at a time across the eight groups.
Network Address
= 2001:db8:acad:1234::/64
Subnet ID (hex)
= 1234
Prefix on Nibble Boundary
= Yes
Host Bits
= 64
How it works
Each 16-bit group keeps only the bits that fall inside the prefix. With the common /48 site prefix and /64 subnets, the fourth group is the subnet identifier you increment per VLAN. Getting the network address wrong in IPv6 is easy because the boundaries are invisible in compressed notation, and a wrong prefix means neighbour discovery never resolves.
Formula
IPv6 Network
network = address AND prefix mask, applied 16 bits at a time across the eight groups.
- p
- Prefix length in bits
- subnetId
- Fourth group, conventionally the site subnet field
Frequently Asked Questions
How is IPv6 Network calculated?
network = address AND prefix mask, applied 16 bits at a time across the eight groups. Each 16-bit group keeps only the bits that fall inside the prefix. With the common /48 site prefix and /64 subnets, the fourth group is the subnet identifier you increment per VLAN.
Why does IPv6 Network matter?
Getting the network address wrong in IPv6 is easy because the boundaries are invisible in compressed notation, and a wrong prefix means neighbour discovery never resolves.
What values do I need to enter?
This calculator takes 2 inputs: IPv6 address, Prefix length. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.