--- 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 ```