Azure Firewall – Where to Start?

About a year ago, Microsoft introduced the first release of Azure Firewall. Since then, and since its general release the service has grown and the features have matured.

To begin, let’s understand what Azure Firewall is? At its core it’s a managed, network security service that protects your Azure Virtual Network resources. It functions as a stateful firewall-as-a-service and offers built-in high availability and scalability. This means you can centrally control, enforce and log all of your network traffic. It fully integrates with Azure Monitor too which means all of the usual logging and analytical goodness.

If the above sounds like something you’d like to use, or at least try, in your Azure environment, read on! To start, let’s break out what can be configured within Azure Firewall and which features could be useful for you.

When deploying an Azure Firewall, you need a couple of things in advance. It needs a dedicated subnet, specifically named “AzureFirewallSubnet” and the minimum size it can be is a /26. It also needs at least one Static Public IP. The Public IP must be on the Standard tier. My recommendation here is to look at creating a Public IP Prefix in advance of creating your Azure Firewall. That way, if you need to delete it and redeploy, you can continue to use the same Public IP again and again. If you want to use multiple Public IPs, it supports up to 100.

So, let’s look at what Azure Firewall (AFW) can do for you on your Virtual Network and then consider some deployment options.

Access

Using your single, or multiple Public IP addresses, AFW allows both source and destination NATing. Meaning it can support multiple inbound ports, such as HTTPS over 443 to different resources. Outbound SNAT helps greatly with services that require white-listing. If you are using multiple Public IPs, AFW randomly picks one for SNAT, so ensure you include all of them in your white-listing requirements.

Protection

AFW uses a Microsoft service called Threat Intelligence filtering. This allows Azure Firewall to alert and deny traffic to and from known malicious IPs and domains. You can turn this setting off, set it to just alert or to both alert and deny. All of the actions are logged.

Filtering

Finally, for filtering, AFW can use both Network Traffic and Application FQDN rules. This means that you can limit traffic to only those explicitly listed within the rule collections. For example, an application rule that only allows traffic to the FQDN – www.wedoazure.ie

A visual representation of the above features is below:

Firewall overview

Now that you understand AFW, let’s look at how to configure to your needs. Normally I would go into the deployment aspect, but it is excellently documented already and relatively easy to follow. However, there are some aspects of the configuration that warrant further detail.

Once deployed, you must create a Custom Route Table to force traffic to your AFW. In the tutorial, it shows you how to create a route for Internet traffic (0.0.0.0/0), however you may want the AFW to be your central control point for your vnet traffic too. Don’t forget, traffic between subnets is not filtered by default. Routing all traffic for each subnet to AFW could allow you to manage which subnet can route where centrally. For example, if we have three subnets, Web, App and DB. A single route table applied to each subnet can tunnel all traffic to AFW. On the AFW you can then allow Web to the Internet and the App subnet. The App subnet can access Web and DB but not Internet and finally the DB subnet can only access the App subnet. This would all be achieved with a single Network Rule collection.

Similarly you can allow/block specific FQDNs with an Application Rule collection. In the tutorial, a single FQDN is allowed. This means that all others are blocked as that is the default behaviour. This might not be practical for your environment and the good news is, you can implement the reverse. With the right priority order, you can allow all traffic except for blocked FQDNs.

A feature you may also want to consider trying is destination NATing. This thankfully has another well documented tutorial on Docs.

Finally, and in some cases most importantly, let’s look at price. You are charged in two ways for AFW. There is a price per-hour-per-instance. That means if you deploy and don’t use it for anything, you will pay approx. €770 per-month (PAYG Calculator). On top of that, you will pay for both data inbound and outbound that is filtered by AFW. You’re charged the same price either direction and that’s approx. €14 per-Tb-per-month. Depending on your environment and/or requirements this price could be OK or too steep. My main advice is to ensure you understand it before deploying!

As always, if there are any questions please get in touch!

How to – Troubleshoot your Azure Virtual Network Gateway

One of the most popular methods of connecting to Azure privately is via VPN. This can be a relatively simple process and is well documented by both Microsoft and 3rd party blogs. However, if you encounter problems, it can be difficult to get the data you need to troubleshoot efficiently. Especially if you don’t have access to both Azure and the local connection appliance.

In this post, I’m going to show you how to troubleshoot a Virtual Network Gateway and its VPN connection. As part of this, there are some required specifics:

If the above lines up with your environment, then let’s get started! (If not, get in touch and I might be able to help)

Troubleshoot a Virtual Network Gateway

Login to the Azure Portal, then click the search bar at the top, type “Network Watcher” and click on it to open your resource.

In the Network Watcher blade, under ‘Network Diagnostic Tools” select ‘VPN Diagnostics’.

You’ll have to choose a Storage Account and a Container within to run the tests. If you don’t have one, you can create one from Network Watcher. The Storage Account doesn’t have to be in the same location as your VNG.

Click the checkbox for the VNG you want to troubleshoot, then click ‘Start Troubleshooting’

Once complete, you will see your ‘Troubleshooting Status’, you can see that for mine above it is shown as ‘Unhealthy’. To get more details, there is a Details pane just below with a ‘Status’ blade giving you more information about the problem and an ‘Action’ blade which gives suggestions on how to resolve the issue.

In this instance, the VNG as a resource is healthy, but the Connection it’s facilitating is not, so we need to dig further.

Troubleshooting a Virtual Network Gateway Connection (VPN)

In the same location we ran troubleshooting for the VNG, we will repeat the steps and select the Connection instead of the VNG this time. Select your Storage Account etc. as before and then click the Connection to troubleshoot. Then click ‘Start Troubleshooting’

Once complete, you will again see a ‘Troubleshooting Status’ and can get more information from the ‘Details’ pane.


As you can see from the above, I have a very simple fix to make, as my pre-shared keys do not match.

Hopefully this helps you out when trying to figure out why those VPN tunnels aren’t working.

As always, if you have any questions, get in touch!

How to – Secure an Application Service with Application Gateway v2

Application Gateway conceptual

Application Gatway v2 brings several welcome additions to the service since it’s initial v1 release. For those who have spent time configuring an Application Gateway, you’ll be glad to hear that udpate/modification times have been drastically reduced. Better performance and the addition of functionality are some of the other main reasons to use v2 over v1. The entire list can be found here.

Recently, I had to secure an Application Service with an Application Gateway v2 on the WAF (web application firewall) tier. This is something I have done several times with v1 without any significant issue. In this instance the Application Service runs on a custom domain as does the Application Gateway. Requirements were to run SSL end to end and have WAF run in prevention mode.

If you’ve ever done this before, you know there are some basics to be completed within your Application Service. For this post and my requirement, they were map a custom domain, runs HTTPS only and prep rules to allow connections only from your Application Gateway. How to do all of that can be found at the following links:

Once your Application Service is ready to go, you move on to configuring your Application Gateway. This is a relatively simple process and can even be completed within the Portal. There is a published guide here. However, once it was configured, I noticed that certain redirect functionality aspects of the application were returning the default host name of the Application Service. This can also happen if you use Azure AD authentication. With WAF in prevention mode, this returns a 403 as a default rule picks up the change in address.

The reason for this is how both Application Gateway and Application Service handle their host headers. To fix this issue, there are two changes you can make, one of which that is only possible on Application Gateway v2.

The v2 only fix is to rewrite the location in the host header using rewrite rules. Rewrite rules are new functionality only included in v2. A guide on what you need to do exactly is here. Make sure the text is exactly as in the guide or it will not work.

The second option, and the one that is more common is to change how your Custom Probe and HTTP settings are configured. The reason for this is that the default guide does not take into account the use of a custom domain on your Application Service. For both settings, modify and remove the ” PickHostNameFromBackendAddress” setting. Now, the Application Gateway will forward the same hostname and redirection will happen on the same too. Full guide here.

As always, if there are any questions on the above, get in touch!

What is Azure Network Security Group?

If you’re considering Azure for IaaS workloads, the first aspect of cloud you will have to understand, design and deploy is networking. As with any other cloud, software defined networking is the foundation of IaaS for Azure.

You cannot deploy a workload without first deploying a Virtual Network. However, once you have a network, you then need to consider its security and specifically how you control its perimeter and access. The perimeter is something that requires its own post but for platform-native, have a look at Azure Firewall and for other topics, start by checking out the Security Center docs for an overview.

When it comes to access control on your Virtual Network, Azure offers built-in solutions for both network layer control and route control. Network Security Groups (NSG) function as the network layer control service. So, what are they and how do you use them?

NSGs filter traffic to and from resources in an Azure Virtual Network. Combining rules that allow or deny traffic for both inbound and outbound traffic, allows granular control at the network layer.

They can be viewed as a basic, stateful, packet filtering firewall, but what does that mean? First, lets note what they don’t do; there is no traffic inspection or authentication access control.

So how do they help secure your network? By combining 5 variables into a scenario which you then allow or deny, you can quickly and easily manipulate the access that is possible to your resource. For example, consider the following two rules:

PriorityPortProtocolSourceDestinationAccess
1003389TCP10.10.10.10*Allow
200****Block

Our first rule, allows RDP traffic to the resources protected by the NSG, but only from the scoped source IP. The second rule, blocks all traffic. The rules are processed in order or priority.

Source and Destination can use IPs, IP ranges, ANY or Service Tags. Service Tags really help you define simple but powerful access rules quickly. For example, consider the following change to our above rules:

PriorityPortProtocolSourceDestinationAccess
1003389TCP10.10.10.10*Allow
101443TCPVirtualNetwork*Allow
200****Block

We still allow RDP and we still block all traffic, however, we now also allow HTTPS traffic from any source tagged as VirtualNetwork. This includes everything in your Virtual Network, any peered Virtual Networks and any traffic originating across a VPN or ExpressRoute. A single Service Tag replaces multiple source ranges and simplifies management.

If you’re still struggling with the filtering aspect, check out this handy tutorial from Docs.

A couple of other items to note about NSGs; they can be applied to a Network Interface or a Subnet and they have some default rules. Which layer you apply an NSG to is important. Remember traffic is processed inbound and outbound in reversed layers. So traffic from a VM out hits Network Interface then Subnet. So how you scope and combine NSGs is critical to ensuring your access control is as you want it. There is a great example of this on Docs.

The default rules that exist within an NSG allow Virtual Network traffic IN and Internet traffic OUT. You can check out the full list for exact details.

As always, if you have any questions or require a steer on a specific scenario, please get in touch!

Azure Networking Updates at Ignite

To say there have been a lot of Azure announcements at Ignite is an understatement. Several important services have hit GA and several exciting new services have been announced. Rather than re-list them all (I’ll link through at the end), I am going to highlight those I am most excited about, and think will be relevant to most clients.

Below is a graphical overview of the new approach to Azure networking, which contains four pillars, Connect, Protect, Deliver and Monitor.

azurenetworkingfalludpate

Starting with Connect, two ExpressRoute related announcements immediately grabbed my attention. Microsoft now offer 100Gbps connectivity speeds via ExpressRoute Direct which is the fastest cloud connectivity available.

Helping customers with geo-distributed offices, ExpressRoute Global Reach was announced, allowing customers to connect offices using their existing circuits. Additional to this concept, Azure Virtual WAN is now GA. With that move, Microsoft also added new preview features including P2S VPN and ExpressRoute connectivity shown below:

vwanfeatures.png

The final announcement in Connect that really will make a difference to clients is Public IP Prefix. This means that you can now request a range of static IP addresses for your resources that you will “own”. This will make white-listing and administration of your public presence a lot simpler.

Moving to the Protect pillar, Azure Firewall has now moved to GA. Which is a great service for those looking to have control over their breakout point in Azure without deploying and maintaining an NVA.

Rounding out Protect, Service Endpoint Policies. These allow more granular control over access to Azure resources over your vnet service endpoint. See previous post on endpoints for more.

From the Deliver pillar, the announcement of Azure Front Door in preview is the big one. AFD is a global entry point for you applications that is scalable and secure. The ability to scale and level of integration with existing services will make this widely used by customers with a large public facing presence.

There are also updates to Application Gateway which improve performance, introduce redundancy and increase the level of integration with over services.

From the final pillar, Monitor, the main announcement is Virtual Network TAP in preview. This allows for continuous mirroring of VM traffic to a collector, without any agents. This the first of these services in a public cloud and will allow for greater analytics and granularity of environment traffic.

For the entire round-up from Microsoft, head here.