How Big Is That Subnet?

I recently had a long list of IPv4 CIDR addresses and wanted to know how many hosts there were in total. Looking at the list, there was a mix of common sizes, /29, /24 and /16 but there were a few I just don’t know off the top of my head. The list was long, and it would have be tedious work manually calculating each.


So, I did what any IT professional in my shoes would do, I wrote some code. The Get-SubnetSize CMDLet will return the total number of usable (often referred to as the number of host) addresses for a specified subnet.

By default, it doesn't count the subnet ID or the broadcast addresses, however, there is a switch -IncludeSubnetIDAndBroadcastAddress, to include those if need them included.

Working with Get-SubnetSize

To work out the size of the subnet, we simply call: Get-SubnetSize -CIDR which will return 254.

Get-SubnetSize -CIDR ’’

Get-SubnetSize -CIDR ’’

What about if we had a subnet mask? Well we can work that out as well! How big is Get-SubnetSize -Subnetmask returns 16777214.

Get-SubnetSize -Subnetmask ''

Get-SubnetSize -Subnetmask ''

How many public IP addresses does Azure use?

Previously I have written about my AzurePublicIPAddresses module in my post, Working with Azure’s public IP addresses. This module allows you to obtain the public IP addresses available in each Azure Region. The module is updated for each new Azure Region that Microsoft introduces.

Combining Get-MicrosoftAzureDatacenterIPRange, Get-SubnetSize and Measure-Object together, we can create a one-liner that will give us the total number of subnets and IP addresses.

Get-MicrosoftAzureDatacenterIPRange | Select-Object -ExpandProperty Subnet | Get-SubnetSize | Measure-Object -Sum
Get-MicrosoftAzureDatacenterIPRange | Select-Object -ExpandProperty Subnet | Get-SubnetSize | Measure-Object -Sum

Get-MicrosoftAzureDatacenterIPRange | Select-Object -ExpandProperty Subnet | Get-SubnetSize | Measure-Object -Sum

And we can see that there are 2621 Subnets and a whopping 7,613,174 IP addresses!!

Getting the module

Posh-SubnetTools is available from the PowerShell Gallery or from the project’s GitHub page.

This module should work with all versions of PowerShell, including PowerShell Core. I have tested the module on PowerShell 5.1 (Windows 10 Insiders).

I appreciate any issues, pull requests or comments that you may have. Have an idea for a new CMDLet, make a pull request and I will include it!

AzurePublicIPAddresses Version 0.7 released

I have just released a new version of my AzurePublicIPAddresses PowerShell module. With this release (version 0.7), support for the UK data centers has been introduced.

You can learn more about using the module from my blog post, Working with Azure’s public IP addresses. James Bannan has put together a post, Update User Defined Routes for Azure Datacenters with Azure Automation, where he talks about updating user defined routes using the information from my module.

The module can be obtained via the PowerShell Gallery or from GitHub.

Kieran Jacobsen

Microsoft Releases PowerShell to Linux and OS X!

The Announcement

On Friday I woke to the remarkable news that PowerShell has been open sourced, and made available on Linux and Mac. You should read the PowerShell Team’s Announcement, and Jeffrey Snover’s announcement. There is an excellent video on Channel 9, PowerShell on Linux and Open Source.

I want to first start by congratulating everyone over at Microsoft, in particular the PowerShell Team and Jeffrey Snover.  I have been an avid user of PowerShell since the codename Monad days and it has been one of the few technology constants in my 10 years in the industry (the other being Active Directory).

It has been a long road since the original Monad Manifesto to reach this milestone, and it could not have been accomplished without Jeffrey’s amazing efforts. Don Jones posted up an excellent article on just why this is such an important accomplishment, you should also read the PowerShell Team's post: Windows PowerShell is now “PowerShell”: An Open Source Project with Linux support – How did we do it?.

This wasn’t an unexpected announcement, in fact, it was quite expected. I never doubted that this accouncement would never occur, to me it wasn't a matter of IF PowerShell would become open source, but WHEN.

Like almost everyone I was in the dark that this was happening, but I had a gut feeling things were close. There were plenty of clues and signs that this was about to happen: .Net Core, Nano Server, Bash on Windows and even the inclusion of Pester in Windows 10. Still, I wasn’t quite expecting to wake up on Friday to the news.

What Was Announced

Microsoft announced that from PowerShell would be run as an open source project, and that an intial alpha release would be made available. This release is version 6.0 and is currently available PowerShell Core, for Windows, Ubuntu, Centos and Mac OS X, with more platforms expected in the future.

So what is PowerShell Core? Core is a cut down version of PowerShell, designed to run on top of the .Net Framework Core edition. We have already seen PowerShell Core in releases of Windows Nano Server. Core edition does not support all of the functionality that the Desktop version will contain.

It is worth noting that this is an alpha release, and as such, you should treat it, and have suitable expectations. This isn’t a production ready release, and likely isn’t going to be for a while yet.

Changes to Remoting

One of the big items in the announcement is the changes to the PowerShell Remoting Protocol (MS-PSRP). Currently the MS-PSRP only supports WinRM, however with PowerShell 6.0, support for SSH will be introduced.

This isn't executing commands over SSH, what is actually occuring is that the objects forming our request are serialized into XML, transmitted over SSH, and then de-serialized. SSH is used as a transport layer for the remoting protocol, mush like WinRM is currently used. SSH is not replacing WinRM, just providing another option for administrators to use.

What this does mean is that you will start to be able to manage your Windows servers from your Macbook, and your Linux servers from your Windows 10 machine. 

I had a significant number of issues with WinRM. From its poor performance to its insecure defaults, and I am hoping that the inclusion of SSH support should start to make a difference. If nothing else, it provides a number of new and interesting ways to design and manage our environments.

What’s Missing?

This is a PowerShell Core release, it is based upon the .Net Core, and as such, some things are just simply not going to be there. It should also be obvious that things like WIM and CIM are not supported and will not be available. Get-EventLog isn't there either, as it doesn't fit with the Linux log file model.

Security Impacts!

Security teams should begin to familiarise themselves with not only PowerShell 6.0 and its remoting changes now, but also with Nano Server prior to their release. With a cross pollination of administration teams, that is, Windows and Linux administrators managing each other's eco systems, we are going to see changes in our network architecture and security requirements. SSH connections from a Windows system will begin to move from the abnormal to the normal.

PowerShell is already a highly desirable target for attackers, with more instances of attacks using PowerShell on a daily basis. With the move to include PowerShell on Linux systems, especially servers, the attraction of PowerShell to attacks is likely to increase. The ability to move from a Windows client to that lovely Red Hat farm makes PowerShell an awesome attacker and Red Team tool. Some in the security industry are already calling PowerShell the next Flash or Java for cross platform hacking.

I guess the other thing we need to consider is that a significant number of people are probably pouring over the PowerShell source code with the intention of finding vulnerabilities. Whilst the chances are probably small that someone might find a significant issue, there is still the possibility.

Other Investments to Watch

Looking through the known issues document, and also the PowerShell Teams announcement, two items stood out to me:

  • The ability to write CMDLets in Python and other languages
  • Unix-style wildcard expansion

Getting Started

The best place to start is the PowerShell Home Page, after that, the PowerShell GitHub repository is your next stop.


It is worth noting that installing PowerShell 6.0 will not replace your existing PowerShell version, it is installed side-by-side. It is also worth noting that this installs Core edition and not Desktop edition.

Simply grab the right MSI, and run the installer


There are official guides for Centos 7, Ubuntu 14.04 and Ubuntu 16.04. The Centos guide should also work for Red Hat.

There are also two great guides:

Mac OS X

You can find Microsoft's instructions for installing here, for more detail check out The IT Hollow's guide, Install PowerShell on Mac.

Other Install Options

There are a bunch of other ways you can get started with PowerShell 6.0:

Once you have PowerShell installed, take a look at some of the demos available.

If you are new to PowerShell and are coming from a Linux or Unix background, check out: A Unix Persons Guide to PowerShell.


The great part of any open source project is that we can all play our own part and contribute. You don’t need to be a developer to contribute either, I often contribute to projects by helping out with documentation, or cleaning up simple default configuration files and example usage.

If you feel like contributing, start by reading the contribution guidelines. I also recommend you take a look at the governance process. The Governance process includes how to raise issues, make contributions, and participate in the design process via RFCs. The documents also provide information on the roles and responsibilities of everyone involved in the project.

I recently spent some time working on some issues with the documentation of the PSScriptAnalyzer. The contribution process is similar to that of PowerShell, and it was super simple and easy to create a pull request and work with the PowerShell Team. I would like to point out that if your pull request is large, you may need to sign the Contribution License Agreement, don’t worry, it isn’t difficult and only takes a few seconds to complete. The agreement just covers that the work you are completing is yours and not of anyone else.

Tool Updates

Update your development tools! Virtual Studio Code (and the PowerShell extension), PSScriptAnalyzer and the ISE Steroids have all been updated to include support for PowerShell 6.0.

More Information

With all of this you should be well on your way to working with PowerShell on Linux and Mac OS X! Good luck and don't forget to share your experiences!

Kieran Jacobsen

PowerShell 5, DSC, SABnzbd and Sonarr (Part 1)

I have been trying to do a lot more with PowerShell DSC of late, including writing my own DSC resources.

Last week, I decided to write some resources for SABnzbd and Sonarr. Why? Well firstly for practice, but also because no one else has looked at building up packages for these apps (there wasn’t even Chocolatey packages).

I am not going to go into detail on implementing classes in PowerShell, instead checkout:


The module cSABnzbd contains a single resource: cSABnzbdInstall. This resource specifying:

  • Ensure: <String> { Ensure | Absent }
  • ServiceCredential: <PSCredential>

If you opt for Ensure to be “Present”, then the resource will install and update SABnzbd. That is right, as new versions are released, it will be automatically updated.

The ServiceCredential allows for us to control what account the SABnzbd services run as. If not specified, LocalHost will be used.


SABnzbd hosts both its source code and its binary releases in GitHub. This is great! GitHub provides a simple REST API that allows us to very easily and dynamically get the latest release for a project.

If we want to get information on the latest release for a particular repository, we simply perform a get request on{owner}/{repo}/releases/latest. The response will contain things like the version name, the release date and the assets in the release. The GitHub API doesn’t need any authentication credentials or tokens; these requests can be performed anonymously.

Performing the API request for sabnzbd the URL for us would be, and the returned information looks like:

The function is pretty simple:


The Get() function is quite easy to implement. We simply need to call Get-Package, and sets the result against the ensure parameter. We then return the object as required. The result is:


The Test() is also pretty simple. We use Get-Package again to see if the package is installed or not.

If Ensure = ‘Present’, then we need to check:

  1. If no package was returned, then return false
  2. If it is installed, compare the installed version to the version number returned using GetLatestVersion()

If Ensure = ‘Absent’, then we simply compare $Package to $null.


Now the Set() function is more complex.

If Ensure = ‘Present’, then we need to:

  1. Find the latest .exe in the release information using GetLatestVersion()
  2. Download the file, this is listed under the assets (look for a .exe).
  3. Silently run setup using the /S switch
  4. Install and start the services (optionally running under the user account specified with ServiceCredential).

If we don’t want SABnzbd installed, then we simply call the uninstall.exe.

Using and Configuring SABnzbd

You should be able to access SABnzbd via http://localhost:8080. When you connect the first time, you will be stepped through the initial setup wizard. I haven’t included any resources for specifying any settings like servers, scheduling or custom folders, you can do this as you would normally do. For more help, try the User Manual.

Getting the module

The module can be found on:

You will need PowerShell 5 or greater installed due to the use of Classes. 

If you encounter any issues, please raise an issue on the GitHub page.

In the next post we will take a look at Sonarr.

Kieran Jacobsen