github.com/hugorut/terraform@v1.1.3/website/docs/language/functions/cidrnetmask.mdx (about)

     1  ---
     2  page_title: cidrnetmask - Functions - Configuration Language
     3  description: |-
     4    The cidrnetmask function converts an IPv4 address prefix given in CIDR
     5    notation into a subnet mask address.
     6  ---
     7  
     8  # `cidrnetmask` Function
     9  
    10  `cidrnetmask` converts an IPv4 address prefix given in CIDR notation into
    11  a subnet mask address.
    12  
    13  ```hcl
    14  cidrnetmask(prefix)
    15  ```
    16  
    17  `prefix` must be given in IPv4 CIDR notation, as defined in
    18  [RFC 4632 section 3.1](https://tools.ietf.org/html/rfc4632#section-3.1).
    19  
    20  The result is a subnet address formatted in the conventional dotted-decimal
    21  IPv4 address syntax, as expected by some software.
    22  
    23  CIDR notation is the only valid notation for IPv6 addresses, so `cidrnetmask`
    24  produces an error if given an IPv6 address.
    25  
    26  -> **Note:** As a historical accident, this function interprets IPv4 address
    27  octets that have leading zeros as decimal numbers, which is contrary to some
    28  other systems which interpret them as octal. We have preserved this behavior
    29  for backward compatibility, but recommend against relying on this behavior.
    30  
    31  ## Examples
    32  
    33  ```
    34  > cidrnetmask("172.16.0.0/12")
    35  255.240.0.0
    36  ```