Creating an Azure Service for Slow Moving Organisations

In this post, I will explain how you can use Azure’s Public IP Prefix feature to pre-create public IP addresses to access Azure services when you are working big/government organisations that can take weeks to configure a VPN tunnel, outbound firewall rule, and so on.

In this scenario, I need a predictable IP address so that means I must use the Standard SKU address tier.

The Problem

It normally only takes a few minutes to create a firewall rule, a VPN tunnel, etc in an on-premises network. But sometimes it seems to take forever! I’ve been in that situation – you’ve set up an environment for the customer to work with, but their on-premises networking team(s) are slow to do anything. And you only wish that you had given them all the details that they needed earlier in the project so their configuration work would end when your weeks of engineering was wrapping up.

But you won’t know the public IP address until you create it. And that is normally only created when you create the virtual network gateway, Azure Firewall, Application Firewall, etc. But what if you had a pool of Azure public IP addresses that were pre-reserved and ready to share with the network team. Maybe they could be used to make early requests for VPN tunnels, firewall rules, and so on? Luckily, we can do that!

Public IP Prefix

An Azure Public IP Prefix is a set of reserved public IP addresses (PIPs). You can create an IP Prefix of a certain size, from /31 (2 addresses) to /24 (256 addresses), in a certain region. The pool of addresses is a contiguous block of predictable addresses. And from that pool, you can create public IP addresses for your Azure resources.

In my example, I want a Standard tier IP address and this requires a Standard tier Public IP Prefix. Unfortunately, the Azure Portal doesn’t allow for this with Public IP Prefix, so we need some PowerShell. First, we’ll define some reused variables:

Now we will create the Publix IP Prefix. Note that the length refers to the subnet mask length. In my example that’s a /30 resulting in a prefix with 4 reserved public IP addresses:

You’ll note above that I used Standard in the command. This creates a pool of static Standard tier public IP addresses. I could have dropped the Standard, and that would have created a pool of static Basic tier IP addresses – you can use the Azure Portal to deploy Basic tier Public IP Prefix and public IP addresses from that prefix. The decision to use Standard tier or Basic tier affects what resources I can deploy with the addresses:

  • Standard: Azure Firewall, zone-redundant virtual network gateways, v2 application gateways/firewalls, standard tier load balancers, etc.
  • Basic static: Basic tier load balancers, v1 application gateways/firewalls, etc.

Note that the non-zone redundant virtual network gateways cannot use static public IP addresses and therefore cannot use Public IP Prefix.

Creating a Public IP Address

Let’s say that I have a project coming up where I need to deploy an Application Firewall and I know the on-premises network team will take weeks to allow outbound access to my new web service. Instead of waiting until I build the application, I can reserve the IP address now, tell the on-premises firewall team to allow it, and then work on my project. Hopefully, by the time I have the site up and running and presented to the Internet by my Application Firewall, they will have created the outbound firewall rule from the company network.

Browse to the Public IP Prefix and make sure that it is in the same region as the new virtual network and virtual network gateway. Open the prefix and check Allocated IP Addresses in the Overview. Make sure that there is free capacity in the reserved block.

Now I can continue to use my variables from above and create a new public IP address from one of the reserved addresses in the Public IP Prefix:

Use the Public IP Address

I now have everything I need to pass onto the on-premises network team in my request. In my example, I am going to create a v2 Application Firewall.

Once I configure the WAF, the on-premises firewall will (hopefully) already have the rule to allow outbound connections to my pre-reserved IP address and, therefore, my new web service.

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