terraform/website/docs/configuration/functions/cidrsubnets.html.md

layout	page_title	sidebar_current	description
functions	cidrsubnets - Functions - Configuration Language	docs-funcs-ipnet-cidrsubnets	The cidrsubnets function calculates a sequence of consecutive IP address ranges within a particular CIDR prefix.

cidrsubnet Function

-> Note: This page is about Terraform 0.12 and later. For Terraform 0.11 and earlier, see 0.11 Configuration Language: Interpolation Syntax.

cidrsubnet calculates a sequence of consecutive IP address ranges within a particular CIDR prefix.

cidrsubnet(prefix, newbits...)

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 related function cidrsubnet. cidrsubnet calculates 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: The Terraform module hashicorp/subnets/cidr wraps 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 platforms.

Examples

> 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 for expressions 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",
  ],
]

Related Functions

• cidrhost calculates the IP address for a single host within a given network address prefix.
• cidrnetmask converts an IPv4 network prefix in CIDR notation into netmask notation.
• cidrsubnet calculates a single subnet address, allowing you to specify its network number.