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

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---
layout: "functions"
page_title: "cidrnetmask - Functions - Configuration Language"
sidebar_current: "docs-funcs-ipnet-cidrnetmask"
description: |-
The cidrnetmask function converts an IPv4 address prefix given in CIDR
notation into a subnet mask address.
---
# `cidrnetmask` Function
-> **Note:** This page is about Terraform 0.12 and later. For Terraform 0.11 and
earlier, see
[0.11 Configuration Language: Interpolation Syntax](../../configuration-0-11/interpolation.html).
`cidrnetmask` converts an IPv4 address prefix given in CIDR notation into
a subnet mask address.
```hcl
cidrnetmask(prefix)
```
`prefix` must be given in IPv4 CIDR notation, as defined in
[RFC 4632 section 3.1](https://tools.ietf.org/html/rfc4632#section-3.1).
The result is a subnet address formatted in the conventional dotted-decimal
IPv4 address syntax, as expected by some software.
CIDR notation is the only valid notation for IPv6 addresses, so `cidrnetmask`
produces an error if given an IPv6 address.
## Examples
```
> cidrnetmask("172.16.0.0/12")
255.240.0.0
```