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Home > Success Center > Engineer's ToolSet (ETS) > Engineer's Toolset Administrator Guide > List of tools included in Engineer's Toolset > Subnet Calculator

Subnet Calculator

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Created by Aileen de Lara_ret, last modified by Aileen de Lara_ret on Jan 13, 2017

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Click Gadgets > Tools > Address Management > Subnet Calculator, and then drag the Subnet Calculator gadget onto a tab.

Address Block Enter an IP address here.
IPv4 or IPv6 Indicates whether the address is IPv4 or IPv6.
Network Mask The subnet mask used when generating a list of IP addresses.
Subnet Bits Number of network (or mask) bits used when generating a subnet list. The number of mask bits automatically adjusts when you change any other parameters.
Number of Subnets The number of subnets to divide the address block into.
Addresses per Subnet The number of host addresses in each subnet.

The bits that identify the address block within an RFC-defined address space. All addresses within the same address space have the same number of prefix bits set to the same value. Visualizing the prefix bits in the address breakdown display can be helpful when an RFC-defined address space does not break down on an octet boundary, that is, the number of prefix bits is not divisible by 8.

For example, the global unicast address space (2000::/3) has 3 prefix bits with values (001), All global unicast addresses start with the same bit pattern of (001). This space ranges from 2000:: to 3FFF.FFFF.FFFF.FFFF.FFFF.FFFF.FFFF.FFFF. Any address block that falls within this address space will have the first three bits identified as prefix bits. Note that the upper bound of the address space does not begin with “20” because the address space does not break as an octet boundary.

2000::/3 = Global unicast
FF00::/8 = Multitask
FE80::/10 = Link-Local unicast
::1/128 = Loopback
::/128 = Unspecified


The bits reserved for identifying the network. The number of network bits will be less than or equal to 64, minus the number of prefix bits.

Theoretically, the address FCFF::, which is a local IPv6 address has 7 prefix bits, could have network bits ranging from 0 (FCFF::/7) to 57 (FCFF::/64)

A concrete instance of the above example would be FCFF::/16 would have 7 prefix bits and 16-17 or 9 network bits. So FCFF=1111 1100 1111 1111 or prefix bits = 1111 110 and network bits = 0 1111 1111.


The bits that are used to uniquely identify the subnets in the network. There can be 2 to the X power of subnets where X is the number of subnet bits.

For example, if there are 3 subnet bits you can have 2 to the 3rd power or 8 subnets.

Last modified
22:07, 12 Jan 2017