CIDR functions for Bicep

Classless Inter-Domain Routing (CIDR) is a method of allocating IP addresses and routing Internet Protocol (IP) packets. This article describes the Bicep functions for working with CIDR.

parseCidr

parseCidr(network)

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

Namespace: sys.

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:

output v4info object = 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:

output v6info object = 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.

Namespace: sys.

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:

output v4subnets array = [for i in range(0, 5): cidrSubnet('10.144.0.0/20', 24, i)]

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:

output v6subnets array = [for i in range(0, 5): cidrSubnet('fdad:3236:5555::/48', 52, i)]

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 we refer to as "usable" IP addresses. So, when the function is passed a hostIndex of 0, 192.168.1.1 is returned.

Within Azure, there are additional IP addresses reserved in each subnet, which include the first four and the last IP address, totaling five reserved IP addresses. For instance, in the case of the IP address range 192.168.1.0/24, the following addresses are reserved:

• 192.168.1.0 : Network address.
• 192.168.1.1 : Reserved by Azure for the default gateway.
• 192.168.1.2, 192.168.1.3 : Reserved by Azure to map the Azure DNS IPs to the VNet space.
• 192.168.1.255 : Network broadcast address.

Namespace: sys.

Parameters

Parameter	Required	Type	Description
network	Yes	string	String containing an IP network to convert. The provided string must be in the correct networking format.
hostIndex	Yes	int	The index determines the host IP address to be returned. If you use the value 0, it gives you the first usable IP address for a non-Azure network. However, if you use 3, it provides you with the first usable IP address for an Azure subnet.

Return value

A string of the IP address.

Examples

The following example calculates the first five usable host IP addresses from the specified /24 on non-Azure networks:

output v4hosts array = [for i in range(0, 5): cidrHost('10.144.3.0/24', i)]

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 on non-Azure networks:

output v6hosts array = [for i in range(0, 5): cidrHost('fdad:3236:5555:3000::/52', i)]

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

• For a description of the sections in a Bicep file, see Understand the structure and syntax of Bicep files.