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cidrsubnets calculates a sequence of consecutive IP address ranges within
a particular CIDR prefix.
prefix must be given in CIDR notation, as defined in
RFC 4632 section 3.1.
The remaining arguments, indicated as
newbits above, each specify the number
of additional network prefix bits for one returned address range. The return
value is therefore a list with one element per
newbits argument, each
a string containing an address range in CIDR notation.
For more information on IP addressing concepts, see the documentation for the
a single subnet address within a prefix while allowing you to specify its
subnet number, while
cidrsubnets can calculate many at once, potentially of
different sizes, and assigns subnet numbers automatically.
When using this function to partition an address space as part of a network address plan, you must not change any of the existing arguments once network addresses have been assigned to real infrastructure, or else later address assignments will be invalidated. However, you can append new arguments to existing calls safely, as long as there is sufficient address space available.
This function accepts both IPv6 and IPv4 prefixes, and the result always uses the same addressing scheme as the given prefix.
Note: As a historical accident, this function interprets IPv4 address octets that have leading zeros as decimal numbers, which is contrary to some other systems which interpret them as octal. We have preserved this behavior for backward compatibility, but recommend against relying on this behavior.
Note: The Terraform module
cidrsubnets to provide additional functionality for assigning symbolic
names to your networks and skipping prefixes for obsolete allocations. Its
documentation includes usage examples for several popular cloud virtual network
> cidrsubnets("10.1.0.0/16", 4, 4, 8, 4) [ "10.1.0.0/20", "10.1.16.0/20", "10.1.32.0/24", "10.1.48.0/20", ] > cidrsubnets("fd00:fd12:3456:7890::/56", 16, 16, 16, 32) [ "fd00:fd12:3456:7800::/72", "fd00:fd12:3456:7800:100::/72", "fd00:fd12:3456:7800:200::/72", "fd00:fd12:3456:7800:300::/88", ]
You can use nested
cidrsubnets calls with
to concisely allocate groups of network address blocks:
> [for cidr_block in cidrsubnets("10.0.0.0/8", 8, 8, 8, 8) : cidrsubnets(cidr_block, 4, 4)] [ [ "10.0.0.0/20", "10.0.16.0/20", ], [ "10.1.0.0/20", "10.1.16.0/20", ], [ "10.2.0.0/20", "10.2.16.0/20", ], [ "10.3.0.0/20", "10.3.16.0/20", ], ]