| --- |
| page_title: cidrhost - Functions - Configuration Language |
| description: |- |
| The cidrhost function calculates a full host IP address within a given |
| IP network address prefix. |
| --- |
| |
| # `cidrhost` Function |
| |
| `cidrhost` calculates a full host IP address for a given host number within |
| a given IP network address prefix. |
| |
| ```hcl |
| cidrhost(prefix, hostnum) |
| ``` |
| |
| `prefix` must be given in CIDR notation, as defined in |
| [RFC 4632 section 3.1](https://tools.ietf.org/html/rfc4632#section-3.1). |
| |
| `hostnum` is a whole number that can be represented as a binary integer with |
| no more than the number of digits remaining in the address after the given |
| prefix. For more details on how this function interprets CIDR prefixes and |
| populates host numbers, see the worked example for |
| [`cidrsubnet`](/language/functions/cidrsubnet). |
| |
| Conventionally host number zero is used to represent the address of the |
| network itself and the host number that would fill all the host bits with |
| binary 1 represents the network's broadcast address. These numbers should |
| generally not be used to identify individual hosts except in unusual |
| situations, such as point-to-point links. |
| |
| This function accepts both IPv6 and IPv4 prefixes, and the result always uses |
| the same addressing scheme as the given prefix. |
| |
| -> **Note:** As a historical accident, this function interprets IPv4 address |
| octets that have leading zeros as decimal numbers, which is contrary to some |
| other systems which interpret them as octal. We have preserved this behavior |
| for backward compatibility, but recommend against relying on this behavior. |
| |
| ## Examples |
| |
| ``` |
| > cidrhost("10.12.112.0/20", 16) |
| 10.12.112.16 |
| > cidrhost("10.12.112.0/20", 268) |
| 10.12.113.12 |
| > cidrhost("fd00:fd12:3456:7890:00a2::/72", 34) |
| fd00:fd12:3456:7890::22 |
| ``` |
| |
| ## Related Functions |
| |
| * [`cidrsubnet`](/language/functions/cidrsubnet) calculates a subnet address under a given |
| network address prefix. |