100 lines
3.0 KiB
Markdown
100 lines
3.0 KiB
Markdown
---
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layout: "functions"
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page_title: "cidrsubnets - Functions - Configuration Language"
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sidebar_current: "docs-funcs-ipnet-cidrsubnets"
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description: |-
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The cidrsubnets function calculates a sequence of consecutive IP address
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ranges within a particular CIDR prefix.
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---
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# `cidrsubnet` Function
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-> **Note:** This page is about Terraform 0.12 and later. For Terraform 0.11 and
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earlier, see
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[0.11 Configuration Language: Interpolation Syntax](../../configuration-0-11/interpolation.html).
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`cidrsubnet` calculates a sequence of consecutive IP address ranges within
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a particular CIDR prefix.
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```hcl
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cidrsubnet(prefix, newbits...)
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```
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`prefix` must be given in CIDR notation, as defined in
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[RFC 4632 section 3.1](https://tools.ietf.org/html/rfc4632#section-3.1).
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The remaining arguments, indicated as `newbits` above, each specify the number
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of additional network prefix bits for one returned address range. The return
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value is therefore a list with one element per `newbits` argument, each
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a string containing an address range in CIDR notation.
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For more information on IP addressing concepts, see the documentation for the
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related function [`cidrsubnet`](./cidrsubnet.html). `cidrsubnet` calculates
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a single subnet address within a prefix while allowing you to specify its
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subnet number, while `cidrsubnets` can calculate many at once, potentially of
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different sizes, and assigns subnet numbers automatically.
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When using this function to partition an address space as part of a network
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address plan, you must not change any of the existing arguments once network
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addresses have been assigned to real infrastructure, or else later address
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assignments will be invalidated. However, you _can_ append new arguments to
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existing calls safely, as long as there is sufficient address space available.
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This function accepts both IPv6 and IPv4 prefixes, and the result always uses
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the same addressing scheme as the given prefix.
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## Examples
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```
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> cidrsubnets("10.1.0.0/16", 4, 4, 8, 4)
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[
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"10.1.0.0/20",
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"10.1.16.0/20",
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"10.1.32.0/24",
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"10.1.48.0/20",
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]
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> cidrsubnets("fd00:fd12:3456:7890::/56", 16, 16, 16, 32)
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[
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"fd00:fd12:3456:7800::/72",
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"fd00:fd12:3456:7800:100::/72",
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"fd00:fd12:3456:7800:200::/72",
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"fd00:fd12:3456:7800:300::/88",
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]
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```
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You can use nested `cidrsubnets` calls with
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[`for` expressions](/docs/configuration/expressions.html#for-expressions)
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to concisely allocate groups of network address blocks:
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```
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> [for cidr_block in cidrsubnets("10.0.0.0/8", 8, 8, 8, 8) : cidrsubnets(cidr_block, 4, 4)]
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[
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[
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"10.0.0.0/20",
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"10.0.16.0/20",
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],
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[
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"10.1.0.0/20",
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"10.1.16.0/20",
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],
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[
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"10.2.0.0/20",
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"10.2.16.0/20",
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],
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[
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"10.3.0.0/20",
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"10.3.16.0/20",
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],
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]
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```
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## Related Functions
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* [`cidrhost`](./cidrhost.html) calculates the IP address for a single host
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within a given network address prefix.
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* [`cidrnetmask`](./cidrnetmask.html) converts an IPv4 network prefix in CIDR
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notation into netmask notation.
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* [`cidrsubnet`](./cidrsubnet.html) calculates a single subnet address, allowing
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you to specify its network number.
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