IPv6 subnet calculator

IPv6 CIDR range for 2001:db8::/121

Calculate the network address, final address, mask, and exact address capacity of any IPv6 CIDR prefix.

Example: 2606:4700::/32

Host bits are normalized to the network address before the range is calculated.

CIDR calculation

Network details for 2001:db8::/121

The prefix identifies a network with 7 host bits. Every address from the first address through the last address belongs to this range.

CIDR prefix

2001:db8::/121

Network mask

ffff:ffff:ffff:ffff:ffff:ffff:ffff:ff80

Prefix length

/121

Host bits

7

First address

2001:db8::

Last address

2001:db8::7f

Total addresses

128

Total addresses (human readable)

2^7 addresses (128)

How this range is calculated

  1. 1The /121 prefix keeps the first 121 network bits fixed.
  2. 2Setting all 7 host bits to zero produces 2001:db8::.
  3. 3Setting those host bits to one produces 2001:db8::7f.

Network address

The normalized prefix base

CIDR notation describes a network, not a single host. If an address with host bits set is entered, this calculator normalizes it to the network base before calculating the range.

Expanded network address

2001:0db8:0000:0000:0000:0000:0000:0000

Recent network calculations

Recent IPv6 CIDR Ranges

Open recent IPv6 prefixes to inspect their normalized range, mask, and address capacity.

Learn how IPv6 CIDR notation and subnet ranges work