github.com/rstandt/terraform@v0.12.32-0.20230710220336-b1063613405c/website/docs/configuration/functions/cidrsubnets.html.md (about)

     1  ---
     2  layout: "functions"
     3  page_title: "cidrsubnets - Functions - Configuration Language"
     4  sidebar_current: "docs-funcs-ipnet-cidrsubnets"
     5  description: |-
     6    The cidrsubnets function calculates a sequence of consecutive IP address
     7    ranges within a particular CIDR prefix.
     8  ---
     9  
    10  # `cidrsubnets` Function
    11  
    12  -> **Note:** This page is about Terraform 0.12 and later. For Terraform 0.11 and
    13  earlier, see
    14  [0.11 Configuration Language: Interpolation Syntax](../../configuration-0-11/interpolation.html).
    15  
    16  `cidrsubnets` calculates a sequence of consecutive IP address ranges within
    17  a particular CIDR prefix.
    18  
    19  ```hcl
    20  cidrsubnets(prefix, newbits...)
    21  ```
    22  
    23  `prefix` must be given in CIDR notation, as defined in
    24  [RFC 4632 section 3.1](https://tools.ietf.org/html/rfc4632#section-3.1).
    25  
    26  The remaining arguments, indicated as `newbits` above, each specify the number
    27  of additional network prefix bits for one returned address range. The return
    28  value is therefore a list with one element per `newbits` argument, each
    29  a string containing an address range in CIDR notation.
    30  
    31  For more information on IP addressing concepts, see the documentation for the
    32  related function [`cidrsubnet`](./cidrsubnet.html). `cidrsubnet` calculates
    33  a single subnet address within a prefix while allowing you to specify its
    34  subnet number, while `cidrsubnets` can calculate many at once, potentially of
    35  different sizes, and assigns subnet numbers automatically.
    36  
    37  When using this function to partition an address space as part of a network
    38  address plan, you must not change any of the existing arguments once network
    39  addresses have been assigned to real infrastructure, or else later address
    40  assignments will be invalidated. However, you _can_ append new arguments to
    41  existing calls safely, as long as there is sufficient address space available.
    42  
    43  This function accepts both IPv6 and IPv4 prefixes, and the result always uses
    44  the same addressing scheme as the given prefix.
    45  
    46  -> **Note:** [The Terraform module `hashicorp/subnets/cidr`](https://registry.terraform.io/modules/hashicorp/subnets/cidr)
    47  wraps `cidrsubnets` to provide additional functionality for assigning symbolic
    48  names to your networks and skipping prefixes for obsolete allocations. Its
    49  documentation includes usage examples for several popular cloud virtual network
    50  platforms.
    51  
    52  ## Examples
    53  
    54  ```
    55  > cidrsubnets("10.1.0.0/16", 4, 4, 8, 4)
    56  [
    57    "10.1.0.0/20",
    58    "10.1.16.0/20",
    59    "10.1.32.0/24",
    60    "10.1.48.0/20",
    61  ]
    62  
    63  > cidrsubnets("fd00:fd12:3456:7890::/56", 16, 16, 16, 32)
    64  [
    65    "fd00:fd12:3456:7800::/72",
    66    "fd00:fd12:3456:7800:100::/72",
    67    "fd00:fd12:3456:7800:200::/72",
    68    "fd00:fd12:3456:7800:300::/88",
    69  ]
    70  ```
    71  
    72  You can use nested `cidrsubnets` calls with
    73  [`for` expressions](/docs/configuration/expressions.html#for-expressions)
    74  to concisely allocate groups of network address blocks:
    75  
    76  ```
    77  > [for cidr_block in cidrsubnets("10.0.0.0/8", 8, 8, 8, 8) : cidrsubnets(cidr_block, 4, 4)]
    78  [
    79    [
    80      "10.0.0.0/20",
    81      "10.0.16.0/20",
    82    ],
    83    [
    84      "10.1.0.0/20",
    85      "10.1.16.0/20",
    86    ],
    87    [
    88      "10.2.0.0/20",
    89      "10.2.16.0/20",
    90    ],
    91    [
    92      "10.3.0.0/20",
    93      "10.3.16.0/20",
    94    ],
    95  ]
    96  ```
    97  
    98  ## Related Functions
    99  
   100  * [`cidrhost`](./cidrhost.html) calculates the IP address for a single host
   101    within a given network address prefix.
   102  * [`cidrnetmask`](./cidrnetmask.html) converts an IPv4 network prefix in CIDR
   103    notation into netmask notation.
   104  * [`cidrsubnet`](./cidrsubnet.html) calculates a single subnet address, allowing
   105    you to specify its network number.