CIDR release notes

Relnotes.md

CIDR Functions

parseCidr(network: string)

Parses an IP address range in CIDR notation and returns an object containing various properties of the address range.

Parameter	Required	Type	Description
network	Yes	string	String containing an IP address range to convert in CIDR format

cidrSubnet(network: string, cidr: int, subnetIndex: int)

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.

Parameter	Required	Type	Description
network	Yes	string	String containing an IP address range to convert in CIDR format
cidr	Yes	int	An integer representing the CIDR to be used to subnet
subnetIndex	Yes	int	Index of the desired subnet IP address range to return

cidrHost(network: string, hostIndex: int)

Calculates the IP address of the host with the specified index on the specified IP address range in CIDR notation. Only considers usable IP addresses.

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.

Sample

/* 
  ----- IPv4 -----
*/

// parse IPv4 CIDR string
output v4info object = parseCidr('10.144.0.0/20')
/* 
Returns:
{
  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
}
*/

// calculate 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)]
/*
Returns:
[
  '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'
]
*/

// calculate the first five usable host IP addresses from the specified /24
output v4hosts array = [for i in range(0, 5): cidrHost('10.144.3.0/24', i)]
/*
Returns:
[
  '10.144.3.1'
  '10.144.3.2'
  '10.144.3.3'
  '10.144.3.4'
  '10.144.3.5'
]
*/

/* 
  ----- IPv6 -----
*/

// parse IPv6 CIDR string
output v6info object = parseCidr('fdad:3236:5555::/48')
/*
Returns:
{
  network: 'fdad:3236:5555::'
  netmask: 'ffff:ffff:ffff::'
  firstUsable: 'fdad:3236:5555::'
  lastUsable: 'fdad:3236:5555:ffff:ffff:ffff:ffff:ffff'
  cidr: 48
}
*/

// calculate 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)]
/*
Returns:
[
  'fdad:3236:5555::/52'
  'fdad:3236:5555:1000::/52'
  'fdad:3236:5555:2000::/52'
  'fdad:3236:5555:3000::/52'
  'fdad:3236:5555:4000::/52'
]
*/

// calculate the first five usable host IP addresses from the specified /52
output v6hosts array = [for i in range(0, 5): cidrHost('fdad:3236:5555:3000::/52', i)]
/*
Returns:
[
  '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'
]
*/

Hi @majastrz , I need a clarification on this as the first 3 host addresses are reserved by Azure.

// Reserved by Azure
  '10.144.3.1'
  '10.144.3.2'
  '10.144.3.3'

Does this mean that the consumers of this function should take this into consideration and plan the usable IP addresses properly?

It will be cool if the function can return the response as below.

// calculate the first five usable host IP addresses from the specified /24
output v4hosts array = [for i in range(0, 5): cidrHost('10.144.3.0/24', i)]

/*
Returns:
[
  '10.144.3.4'
  '10.144.3.5'
  '10.144.3.6'
  '10.144.3.7'
  '10.144.3.8'
]
*/

Yes, the first 3 host addresses are reserved in Azure subnets. See Azure/bicep#10822 for more details.

For variable size subnets, can you open a new issue to track the feature request?

I would offer that forcing the function to skip the first 3 would limit it's application to non-Azure CIDR values, such as when calculating first/last usable for a CIDR from an external network to configure firewall rules. Those external networks don't necessarily skip the first 3 like Azure does.

If we need to skip the first few for an Azure CIDR, we should be able to just start the range at something higher than 0, correct?

I would offer that forcing the function to skip the first 3 would limit it's application to non-Azure CIDR values, such as when calculating first/last usable for a CIDR from an external network to configure firewall rules. Those external networks don't necessarily skip the first 3 like Azure does.

If we need to skip the first few for an Azure CIDR, we should be able to just start the range at something higher than 0, correct?

Yes and we have no intention of changing the current behavior of the cidrHost() function. However, we will likely add a new optional parameter to the function to let users customize the behavior.

I am trying to create subnet address spaces using cidrSubnet but my CIDR blocks are not same

param vnetAddressSpace string = '10.238.0.64/27'

output address1 string = cidrSubnet(vnetAddressSpace,28,0)
output address2 string = cidrSubnet(vnetAddressSpace,29,1)
output address3 string = cidrSubnet(vnetAddressSpace,29,2)

If I see the output, the values are
address1= 10.238.0.64/28
address2= 10.238.0.72/29
address3= 10.238.0.80/29

As you can see the address2 is wrong. Is this a bug or a limitation?

@patild05 Can you open an issue for this? It'll be easier to have a conversation about this particular issue and easier to track on our side.