2018-05-13 23:11:13 +02:00
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---
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layout: "functions"
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2018-12-20 05:35:11 +01:00
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page_title: "cidrnetmask - Functions - Configuration Language"
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2018-05-13 23:11:13 +02:00
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sidebar_current: "docs-funcs-ipnet-cidrnetmask"
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description: |-
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The cidrnetmask function converts an IPv4 address prefix given in CIDR
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notation into a subnet mask address.
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---
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# `cidrnetmask` Function
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`cidrnetmask` converts an IPv4 address prefix given in CIDR notation into
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a subnet mask address.
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```hcl
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cidrnetmask(prefix)
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```
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`prefix` must be given in IPv4 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 result is a subnet address formatted in the conventional dotted-decimal
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IPv4 address syntax, as expected by some software.
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CIDR notation is the only valid notation for IPv6 addresses, so `cidrnetmask`
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produces an error if given an IPv6 address.
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## Examples
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```
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> cidrnetmask("172.16.0.0/12")
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255.240.0.0
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```
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