57 lines
1.9 KiB
Markdown
57 lines
1.9 KiB
Markdown
---
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layout: "language"
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page_title: "cidrhost - Functions - Configuration Language"
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sidebar_current: "docs-funcs-ipnet-cidrhost"
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description: |-
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The cidrhost function calculates a full host IP address within a given
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IP network address prefix.
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---
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# `cidrhost` Function
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`cidrhost` calculates a full host IP address for a given host number within
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a given IP network address prefix.
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```hcl
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cidrhost(prefix, hostnum)
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```
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`prefix` must be given in 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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`hostnum` is a whole number that can be represented as a binary integer with
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no more than the number of digits remaining in the address after the given
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prefix. For more details on how this function interprets CIDR prefixes and
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populates host numbers, see the worked example for
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[`cidrsubnet`](./cidrsubnet.html).
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Conventionally host number zero is used to represent the address of the
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network itself and the host number that would fill all the host bits with
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binary 1 represents the network's broadcast address. These numbers should
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generally not be used to identify individual hosts except in unusual
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situations, such as point-to-point links.
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This function accepts both IPv6 and IPv4 prefixes, and the result always uses
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the same addressing scheme as the given prefix.
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-> **Note:** As a historical accident, this function interprets IPv4 address
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octets that have leading zeros as decimal numbers, which is contrary to some
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other systems which interpret them as octal. We have preserved this behavior
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for backward compatibility, but recommend against relying on this behavior.
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## Examples
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```
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> cidrhost("10.12.112.0/20", 16)
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10.12.112.16
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> cidrhost("10.12.112.0/20", 268)
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10.12.113.12
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> cidrhost("fd00:fd12:3456:7890:00a2::/72", 34)
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fd00:fd12:3456:7890::22
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```
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## Related Functions
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* [`cidrsubnet`](./cidrsubnet.html) calculates a subnet address under a given
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network address prefix.
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