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tm_cidrsubnets Function ​

tm_cidrsubnets calculates a sequence of consecutive IP address ranges within a particular CIDR prefix.

hcl
tm_cidrsubnets(prefix, newbits...)

prefix must be given in CIDR notation, as defined in RFC 4632 section 3.1.

The remaining arguments, indicated as newbits above, each specify the number of additional network prefix bits for one returned address range. The return value is therefore a list with one element per newbits argument, each a string containing an address range in CIDR notation.

For more information on IP addressing concepts, see the documentation for the related function tm_cidrsubnet. tm_cidrsubnet calculates a single subnet address within a prefix while allowing you to specify its subnet number, while tm_cidrsubnets can calculate many at once, potentially of different sizes, and assigns subnet numbers automatically.

When using this function to partition an address space as part of a network address plan, you must not change any of the existing arguments once network addresses have been assigned to real infrastructure, or else later address assignments will be invalidated. However, you can append new arguments to existing calls safely, as long as there is sufficient address space available.

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 ​

tm_cidrsubnets("10.1.0.0/16", 4, 4, 8, 4)
[
  "10.1.0.0/20",
  "10.1.16.0/20",
  "10.1.32.0/24",
  "10.1.48.0/20",
]

tm_cidrsubnets("fd00:fd12:3456:7890::/56", 16, 16, 16, 32)
[
  "fd00:fd12:3456:7800::/72",
  "fd00:fd12:3456:7800:100::/72",
  "fd00:fd12:3456:7800:200::/72",
  "fd00:fd12:3456:7800:300::/88",
]

You can use nested tm_cidrsubnets calls with for expressions to concisely allocate groups of network address blocks:

tm_[for cidr_block in cidrsubnets("10.0.0.0/8", 8, 8, 8, 8) : cidrsubnets(cidr_block, 4, 4)]
[
  [
    "10.0.0.0/20",
    "10.0.16.0/20",
  ],
  [
    "10.1.0.0/20",
    "10.1.16.0/20",
  ],
  [
    "10.2.0.0/20",
    "10.2.16.0/20",
  ],
  [
    "10.3.0.0/20",
    "10.3.16.0/20",
  ],
]
  • tm_cidrhost calculates the IP address for a single host within a given network address prefix.
  • tm_cidrnetmask converts an IPv4 network prefix in CIDR notation into netmask notation.
  • tm_cidrsubnet calculates a single subnet address, allowing you to specify its network number.