Azure

A collection of scripts I use for Azure related things.

IPv6

File: Get-AzPrivateIPv6Subnet.ps1

This script generates an Azure compatible Local Unicast IPv6 address space based on RFC 4193. The script uses "fd" as the base IPv6 prefix, followed by a single 40-bit pseudo-random Global ID, and initially creates a single pseudo-random 16-bit Subnet ID.

  | 7 bits |1|  40 bits   |  16 bits  |          64 bits           |
  +--------+-+------------+-----------+----------------------------+
  | Prefix |L| Global ID  | Subnet ID |        Interface ID        |
  +--------+-+------------+-----------+----------------------------+

Properties

[string]Prefix

This value MUST BE "fd", per RFC 4193, until a future RFC defines the 0 value for the L bit.

[string]GlobalID

This it the 40-bit pseudo-random Global ID. There MUST BE only a single GlobalID per instance.

[string[]]SubnetID

A string array of 16-bit pseudo-random Subnet IDs. The theoretical limit of this is 2^16, or 65536 subnets per Global ID.

Methods

GetAzVnet()

Outputs the /48 subnet string. This can be used as the Azure virtual network (vnet) address space.

GetAzSubnet([int|string])

Outputs the /64 subnet string. This can be used as the address space for a single subnet within the vnet with the matching Global ID (see GetAzVnet()).

int

This is the array position, within SubnetID, that must be used to generate the address space string.

string

The Subnet ID string, within SubnetID, that must be used to generate the address space string. The string must be in SubnetID.

AddAzSubnet()

Generates a new Subnet ID and adds it to

Usage

# create the base /48 with a randomly generated Global ID and Subnet ID
$ipv6 = iwr https://raw.githubusercontent.com/JamesKehr/Azure/main/Get-AzPrivateIPv6Subnet.ps1 | iex

# get the Global ID
$ipv6.GlobalID

# get the array of Subnet IDs
$ipv6.SubnetID

# output the Azure vnet subnet string
# which is the fd:<Global ID>::/48 string used as the Azure Virtual Network IPv6 address space
$ipv6.GetAzVnet()

# output the default, auto-generated, subnet strung
# used by a subnet within the vnet, using the format: fd:<Global ID>:<Subnet ID>::/64
# the int is based on programming array standard, so the first position is 0, not 1.
$ipv6.GetAzSubnet(0)

# -OR-
$ipv6.GetAzSubnet($ipv6.SubnetID[0])

# generate a new psudeo-random Subnet ID
$ipv6.AddSubnetID()

# this adds a new entry into the SubnetID list
$ipv6.SubnetID

# output the subnet address for the newly generated Subnet ID
$ipv6.GetAzSubnet(1)

To-do

• Use .NET Security.Cryptography.RNGCryptoServiceProvider to generate the Global ID and Subnet ID's.
• Validate that a new Subnet ID is unique within the array. There is currently a smallish chance that there will be duplication after a significant number of Subnet ID's have been generated.
• Make $Prefix a static property. The RFC currently does not define the L-bit being 0, so only "fd" can be used to remain RFC compliant.
• Switch SubnetID to a .NET generic list. This will give me IndexOf([string]) to quickly find the index of a SubnetID, which can be used in GetAzSubnet(int) to reduce duplication of effort.

https://learn.microsoft.com/en-us/powershell/scripting/learn/deep-dives/everything-about-arrays?view=powershell-7.3#generic-list

• The move to Generic lists will require all SubnetIDs be in lower case since IndexOf is case sensitive.