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CIDR functions for ARM templates

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This article describes the functions for working with CIDR in your Azure Resource Manager template (ARM template).

Tip

We recommend Bicep because it offers the same capabilities as ARM templates and the syntax is easier to use. To learn more, see cidr functions.

parseCidr

parseCidr(network)

Parses an IP address range in CIDR notation to get various properties of the address range.

In Bicep, use the parseCidr function.

Parameters

Parameter Required Type Description
network Yes string String in CIDR notation containing an IP address range to be converted.

Return value

An object that contains various properties of the address range.

Examples

The following example parses an IPv4 CIDR string:

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "resources": [],
  "outputs": {
    "v4info": {
      "type": "object",
      "value": "[parseCidr('10.144.0.0/20')]"
    }
  }
}

The preceding example returns the following object:

{
  "network":"10.144.0.0",
  "netmask":"255.255.240.0",
  "broadcast":"10.144.15.255",
  "firstUsable":"10.144.0.1",
  "lastUsable":"10.144.15.254",
  "cidr":20
}

The following example parses an IPv6 CIDR string:

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "resources": [],
  "outputs": {
    "v6info": {
      "type": "object",
      "value": "[parseCidr('fdad:3236:5555::/48')]"
    }
  }
}

The preceding example returns the following object:

{
  "network":"fdad:3236:5555::",
  "netmask":"ffff:ffff:ffff::",
  "firstUsable":"fdad:3236:5555::",
  "lastUsable":"fdad:3236:5555:ffff:ffff:ffff:ffff:ffff",
  "cidr":48
}

cidrSubnet

cidrSubnet(network, newCIDR, subnetIndex)

Splits the specified IP address range in CIDR notation into subnets with a new CIDR value and returns the IP address range of the subnet with the specified index.

In Bicep, use the cidrSubnet function.

Parameters

Parameter Required Type Description
network Yes string String containing an IP address range to convert in CIDR notation.
newCIDR Yes int An integer representing the CIDR to be used to subnet. This value should be equal or larger than the CIDR value in the network parameter.
subnetIndex Yes int Index of the desired subnet IP address range to return.

Return value

A string of the IP address range of the subnet with the specified index.

Examples

The following example calculates the first five /24 subnet ranges from the specified /20:

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "resources": [],
  "outputs": {
    "v4subnets": {
      "type": "array",
      "copy": {
        "count": "[length(range(0, 5))]",
        "input": "[cidrSubnet('10.144.0.0/20', 24, range(0, 5)[copyIndex()])]"
      }
    }
  }
}

The preceding example returns the following array:

[
  "10.144.0.0/24",
  "10.144.1.0/24",
  "10.144.2.0/24",
  "10.144.3.0/24",
  "10.144.4.0/24"
]

The following example calculates the first five /52 subnet ranges from the specified /48:

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "resources": [],
  "outputs": {
    "v6subnets": {
      "type": "array",
      "copy": {
        "count": "[length(range(0, 5))]",
        "input": "[cidrSubnet('fdad:3236:5555::/48', 52, range(0, 5)[copyIndex()])]"
      }
    }
  }
}

The preceding example returns the following array:

[
  "fdad:3236:5555::/52"
  "fdad:3236:5555:1000::/52"
  "fdad:3236:5555:2000::/52"
  "fdad:3236:5555:3000::/52"
  "fdad:3236:5555:4000::/52"
]

cidrHost

cidrHost(network, hostIndex)

Calculates the usable IP address of the host with the specified index on the specified IP address range in CIDR notation. For example, in the case of 192.168.1.0/24, there are reserved IP addresses: 192.168.1.0 serves as the network identifier address, while 192.168.1.255 functions as the broadcast address. Only IP addresses ranging from 192.168.1.1 to 192.168.1.254 can be assigned to hosts, which are referred to as "usable" IP addresses. So, when the function is passed a hostIndex of 0, 192.168.1.1 is returned.

In Bicep, use the cidrHost function.

Parameters

Parameter Required Type Description
network Yes string String containing an ip network to convert (must be correct networking format).
hostIndex Yes int The index of the host IP address to return.

Return value

A string of the IP address.

Examples

The following example calculates the first five usable host IP addresses from the specified /24:

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "resources": [],
  "outputs": {
    "v4hosts": {
      "type": "array",
      "copy": {
        "count": "[length(range(0, 5))]",
        "input": "[cidrHost('10.144.3.0/24', range(0, 5)[copyIndex()])]"
      }
    }
  }
}

The preceding example returns the following array:

[
  "10.144.3.1"
  "10.144.3.2"
  "10.144.3.3"
  "10.144.3.4"
  "10.144.3.5"
]

The following example calculates the first five usable host IP addresses from the specified /52:

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "resources": [],
  "outputs": {
    "v6hosts": {
      "type": "array",
      "copy": {
        "count": "[length(range(0, 5))]",
        "input": "[cidrHost('fdad:3236:5555:3000::/52', range(0, 5)[copyIndex()])]"
      }
    }
  }
}

The preceding example returns the following array:

[
  "fdad:3236:5555:3000::1"
  "fdad:3236:5555:3000::2"
  "fdad:3236:5555:3000::3"
  "fdad:3236:5555:3000::4"
  "fdad:3236:5555:3000::5"
]

Next steps