Azure Firewall DNAT is a pivotal feature within the Azure Firewall suite, designed to orchestrate the redirection of network traffic from a designated public IP address or port to an alternative destination within the Azure cloud platform. This functionality becomes indispensable in scenarios where you need to expose internal services securely to the public internet or reorient traffic flow towards particular services or servers. The pricing structure for Azure Firewall is multifaceted, influenced by factors such as the number of configured rules, data processing volumes, and the utilization of availability zones; precise cost details are readily available on the official Azure pricing portal.

Key attributes defining Azure Firewall DNAT include:

• Inbound Traffic Rerouting: At its core, DNAT facilitates the rerouting of incoming traffic that arrives at a specified port or IP address to a predetermined internal IP address and port within your Azure Virtual Private Network (VPN). This is instrumental in unveiling internal services or resources to external users while meticulously controlling access, or in altering the trajectory of traffic flows.
• Port Mapping Capabilities: Destination Network Address Translation, or DNAT, is strategically employed to map traffic from a distinct port on Azure Firewall’s public IP address to a chosen internal IP address and its corresponding port. This intricate mapping enables the hosting of services like web servers or application servers securely behind the Azure Firewall, rendering them accessible from the vast expanse of the internet.
• Seamless Load Balancer Integration: Azure Firewall DNAT can be synergistically combined with Azure Load Balancer to construct robust and scalable solutions. By meticulously configuring DNAT rules within Azure Firewall, you can channel incoming traffic to backend pool members managed by the load balancer, thereby unlocking enhanced scalability, superior high availability, and efficient load-balancing functionalities.
• Application Exposure with Security: DNAT provides a fortified pathway for publishing internal applications or services to the internet while ensuring their protection behind the formidable Azure Firewall. It offers a secure conduit to unveil specific resources or services to external clients, with access meticulously governed by the comprehensive Azure Firewall rules and policies.
• Preservation of Source IP Address: A significant advantage of utilizing DNAT for traffic redirection is the immutable preservation of the source IP address. This critical characteristic allows the ultimate destination resource to discern the original source IP address of the client initiating the request. This feature is invaluable for accurate auditing, streamlined troubleshooting, and maintaining transparent visibility into the client’s originating IP address.
• Granular Rule-Based Configuration: Azure Firewall DNAT rules are meticulously crafted and organized within Azure Firewall’s rule collection hierarchy. You possess the ability to formulate sophisticated rule sets that precisely delineate source IP addresses, destination IP addresses, ports, and protocols for traffic redirection. The flexibility to establish multiple DNAT rules caters to a diverse array of scenarios and application requirements.

Deconstructing DNAT Rules within Azure Firewall

The configuration of Azure Firewall Destination Network Address Translation (DNAT) is imperative for effectively filtering inbound internet traffic to designated subnets. Upon the completion of the DNAT configuration, the action associated with the NAT rule collection will dynamically transition to ‘DNAT’. Each individual rule articulated within the NAT rule can be leveraged to translate the firewall’s public IP address and port into a private IP address and its corresponding port.

By meticulously configuring DNAT rules within Azure Firewall policies, you gain an unparalleled degree of dominion over incoming traffic, thereby significantly bolstering security posture and ensuring that the appropriate data reaches its intended destination. This capability is particularly invaluable for organizations striving to safeguard their precious resources while simultaneously providing necessary access to specific, authorized services.

It is noteworthy that DNAT implicitly appends a network rule to permit the traffic that has undergone translation. For heightened security efficacy, the recommended approach involves adding a precisely defined internet source to grant DNAT access to the network, unequivocally discouraging the indiscriminate use of wildcards.

DNAT rules can be employed to both permit and restrict inbound traffic traversing a firewall’s public IP address. The judicious application of a DNAT rule becomes essential when the requirement arises to convert a public IP address into a private counterpart. Azure Firewall’s public IP addresses serve as the primary conduits for incoming internet traffic, diligently filtering and transforming this traffic to establish connectivity with internal resources domiciled within Azure.

Unveiling the Intricacies: A Meticulous Guide to Filtering Inbound Internet Traffic with Azure Firewall Policy DNAT

The contemporary digital landscape, increasingly characterized by an omnipresent nexus of interconnected systems and the pervasive threat of malicious cyber incursions, mandates an uncompromising approach to network security. Within the expansive dominion of cloud computing, particularly the robust ecosystem offered by Microsoft Azure, the strategic implementation of a managed network security service like Azure Firewall becomes not merely advantageous but absolutely indispensable. This comprehensive exposition endeavors to delineate, with painstaking precision, a detailed, hands-on methodology for configuring Azure Firewall Destination Network Address Translation (DNAT). The overarching objective of this intricate configuration is to rigorously filter inbound internet traffic, thereby fortifying your cloud-based resources against unauthorized access and potential digital reconnaissance from the vast, untamed expanse of the global internet. The process involves a symphony of interconnected Azure services, each playing a vital role in constructing a resilient and impenetrable digital perimeter. Understanding the fundamental principles of network segmentation, traffic flow control, and identity-based access management forms the bedrock upon which this advanced configuration is meticulously erected. This guide seeks to demystify the complex choreography of these elements, empowering architects and engineers to deploy robust security postures.

Embarking on Your Expedition: Accessing the Azure Portal

To commence this intricate and multifaceted configuration journey, your initial and paramount step involves navigating with deliberate intent to the Azure portal. This digital nexus, serving as the centralized administrative console for all Azure resources, can be expeditiously accessed by either initiating a click upon the designated ‘Open Console’ button, typically provided within a learning environment or a managed service interface, or by directly inputting the universally recognized and canonical URL: https://portal.azure.com. The expediency of this access point belies the profound depth of functionality and control it subsequently bestows upon the diligent administrator.

For the purpose of ensuring a truly seamless, unhindered, and optimally efficient experience throughout the entirety of this intricate configuration process, it is not merely suggested but stringently recommended to meticulously utilize an incognito or private browsing window. This judicious choice serves as a crucial prophylactic measure, meticulously designed to circumvent a litany of potential discrepancies that can regrettably arise from persistent caching mechanisms or lingering session artifacts within the standard browse window environment. Browsers, in their tireless endeavor to optimize user experience and expedite page loading, frequently store temporary files, cookies, and session data. While generally beneficial, these cached elements can, on occasion, lead to an unintended automatic login to a previously accessed, and potentially erroneous, Azure account, or even present stale configuration data, thereby introducing an element of undesirable incongruity into your current operational session.

In the regrettable eventuality that the Azure portal, exhibiting an unwelcome autonomy, inadvertently and automatically logs you into an unintended, or indeed an incorrect, Azure account, it is absolutely imperative that you adhere to a prescribed sequence of corrective actions with unwavering precision. Your immediate subsequent course of action must be to execute a complete and unequivocal logout from the current, erroneous session. Following this, it is equally vital to meticulously clear your browser’s entire cache; this often involves navigating through browser settings to a ‘Privacy and Security’ or ‘History’ section and selecting options to clear ‘cached images and files’ and ‘cookies and other site data’. Once these preparatory steps are scrupulously completed, you can then proceed with the utmost care to meticulously sign in anew, utilizing your accurately designated username and corresponding password. This fastidious adherence to proper session management ensures that your configuration endeavors within the Azure portal are conducted within a pristine, controlled, and precisely aligned digital environment, thereby minimizing the potential for configuration errors stemming from environmental factors rather than user input. Furthermore, always ensure that your user account possesses the requisite Azure Role-Based Access Control (RBAC) permissions, such as ‘Contributor’ or ‘Owner’ within the target subscription or resource group, to successfully execute the resource provisioning and configuration steps outlined herein. Without appropriate permissions, even the most meticulous sign-in process will prove futile in achieving the desired configuration outcomes.

Constructing Your Network Cornerstone: Establishing a Hub Virtual Network (VNet)

Within the expansive and intuitively navigable landscape of the Azure portal, your next critical architectural endeavor involves the foundational construction of a Hub Virtual Network (VNet). This VNet will serve as the central nexus of your network topology, embodying the quintessential element of a hub-and-spoke network architecture. This architectural pattern is not merely an arbitrary design choice; it is a meticulously engineered paradigm that promotes centralized security, shared services, and simplified connectivity for disparate workloads. The hub typically hosts shared services like Azure Firewall, VPN gateways, ExpressRoute gateways, and potentially shared monitoring or identity services. The spokes, conversely, house the actual application workloads, maintaining a segregated and compartmentalized environment. This separation inherently enhances security posture by preventing direct communication between spokes, forcing all inter-spoke and internet-bound traffic through the centralized security controls of the hub.

To initiate this foundational deployment, locate and judiciously employ the omnipresent search bar, strategically positioned at the zenith of the Azure interface. Into this search bar, input the precise phrase “Virtual network.” From the subsequent array of search results, which are dynamically curated to reflect your input, meticulously select the entry unequivocally labeled “Virtual Networks.” This action will transport you to the dedicated management blade for virtual networks, presenting an aggregated view of any existing VNets within your current subscription. Subsequently, with deliberate intent, locate and initiate a click upon the prominent “+ Create” button, typically situated within the upper echelon of the Virtual Networks section. This action will invoke the creation wizard, guiding you through the systematic definition of your new virtual network.

Upon arrival at the “Create virtual network” page, your initial focus must be directed towards the “Basics” tab. Here, you are necessitated to populate a series of foundational parameters with scrupulous attention to detail:

• Resource group: This critical parameter mandates that you either define a new resource group or select an appropriate, pre-existing resource group from a dropdown list. A resource group in Azure serves as a logical container for related resources, facilitating their collective management, monitoring, and lifecycle governance. It is a fundamental organizational unit that streamlines deployment, simplifies cost tracking, and enables coherent application of policies and access controls. For optimal practice, all resources pertaining to this specific firewall deployment (e.g., VNets, Firewall, VMs) should ideally reside within the same dedicated resource group.
• Name: Bestow a meaningful, descriptive, and easily discernible name upon your hub VNet. For instance, a nomenclature such as “MyHubVNet” offers clarity and immediate identification of its architectural role. The chosen name should reflect its purpose and position within your broader cloud infrastructure.
• Region: The selection of a geographical region is a critically strategic decision that must unequivocally align with your overarching deployment strategy, data residency requirements, and latency considerations. Proximity to your end-users or other interconnected Azure services can significantly impact performance. For consistency within this guided configuration, maintaining geographical coherence between your hub and spoke VNets is paramount.

Upon the meticulous completion of the “Basics” tab, your attention must then seamlessly transition to the “IP Addresses” tab. This can be accomplished either by directly clicking on the “IP Addresses” tab heading or by utilizing the convenient “Next: IP Addresses” button, typically situated at the bottom-right quadrant of the page. Within the “IP Addresses” tab, a primary directive is to specify the IPv4 address space for your hub VNet. A conventional and highly recommended choice for this central network is to assign a CIDR block such as 10.0.0.0/16. This particular address space provides an ample range of approximately 65,536 available IP addresses, offering significant room for the proliferation of various subnets and hosted services within the hub, thereby accommodating future expansion without the immediate exigency for network re-architecting.

Immediately beneath the “Subnet name” field, you will discern a pre-provisioned entry labeled “default.” It is imperative that you initiate a click on this “default” entry. This action will subsequently expose the “Edit Subnet” section, enabling the precise configuration of your first, and critically important, subnet within the hub VNet. Within this “Edit Subnet” interface, you are required to provide the following details:

• Subnet name: This is a particularly sensitive and mandatory subnet name for the Azure Firewall service. You must precisely enter “AzureFirewallSubnet”. Any deviation from this exact string will result in the inability to deploy the Azure Firewall into this VNet. This requirement underscores the tight integration and specialized provisioning needs of managed Azure services.
• Subnet address range: Assign a suitable and non-overlapping subnet address range that is logically contained within your broader 10.0.0.0/16 VNet address space. For example, 10.0.0.0/24 would allocate 256 IP addresses (with 5 reserved by Azure), which is generally sufficient for the firewall itself and any associated management interfaces. Upon meticulous completion of these parameters, secure your configurations by initiating a click on “Save.”

Finally, with all foundational network parameters meticulously defined, conclude this stage of the deployment by initiating a click on “Review + Create,” allowing Azure to perform a final validation of your configuration against its internal policies and resource availability. Once the validation process successfully completes, indicated by a green checkmark, proceed to click “Create.” It is important to temper expectations regarding deployment immediacy; this particular provisioning step, encompassing the creation of a virtual network and its designated subnet, may, by its very nature, necessitate a few minutes for complete and robust provisioning within the distributed Azure infrastructure. During this brief interval, Azure orchestrates the allocation of network resources, ensuring global consistency and connectivity, a process that inherently requires a short but unavoidable temporal expenditure. Patience during this phase is advisable, allowing the underlying cloud fabric to seamlessly establish your network’s core.

Expanding Your Network Canvas: Establishing a Spoke Virtual Network (VNet)

To further augment and intelligently extend your nascent network topology, aligning with the principles of the hub-and-spoke architecture that underpins robust cloud deployments, your next strategic undertaking involves the creation of a Spoke Virtual Network (VNet). This spoke VNet will serve as the dedicated host for your application workloads, providing an isolated and manageable environment for specific services or departments. The segregation of workloads into distinct spoke VNets enhances security by limiting lateral movement in the event of a breach and simplifies network management by isolating specific application dependencies.

Within the same Virtual networks interface, where you previously provisioned your hub VNet, locate and initiate a click upon the ubiquitous “+ Create” button once more. This action will again invoke the “Create Virtual Network” wizard, prompting you to systematically define the characteristics of your new spoke network.

On the “Create Virtual Network” page, your initial focus should again reside within the “Basics” tab. Here, it is imperative that you furnish the following essential details with unwavering precision:

• Resource group: For consistency, simplified management, and coherent billing, it is a recommended best practice to select the same resource group that was previously utilized for the deployment of your hub VNet. This adherence to a unified resource group (e.g., resource_group_XXXXX) streamlines administrative overhead and reinforces the logical grouping of related cloud assets.
• Name: Assign a distinct, easily identifiable, and semantically meaningful name to your spoke VNet. A nomenclature such as “MySpokeVNet” provides immediate clarity regarding its role within your network architecture. This clear naming convention becomes increasingly vital as your cloud infrastructure expands and encompasses a multitude of virtual networks.
• Region: To ensure optimal performance, minimize inter-regional latency, and align with disaster recovery strategies, it is strongly advised to opt for the same geographical region that was meticulously chosen for the deployment of your hub VNet. For illustrative consistency within this guide, the region typically designated as “(US) East US” serves as an exemplary choice. Maintaining regional contiguity is a cornerstone of efficient and high-performing cloud network designs, preventing unnecessary data egress costs and complex routing.

Upon the meticulous completion of the “Basics” tab, your attention must then transition with seamless fluidity to the “IP Addresses” tab. This critical section dictates the internal address space for your spoke VNet. Here, a primary and fundamental directive is to adjust the default IPv4 address space that Azure automatically provisions. It is crucial to assign a distinct and non-overlapping private IPv4 address space that is entirely separate from the address space utilized by your hub VNet. For instance, a highly conventional and effective choice for this spoke network would be 192.168.0.0/16. The absolute necessity of non-overlapping IP address ranges between the hub and spoke VNets cannot be overstressed; any overlap would fundamentally impede the establishment of VNet peering, the mechanism by which these separate networks will ultimately communicate, leading to unresolvable routing conflicts.

Having defined the broader VNet address space, your next crucial step within the “IP Addresses” tab involves the meticulous management of subnets. It is absolutely imperative that you initiate the deletion of the “Default Subnet” that is automatically provisioned by Azure upon the creation of a new VNet. This default subnet often comes with a generic address range that may not align with your specific architectural requirements or future subnetting plans. After its removal, proceed to initiate a click on the prominent “+ Add Subnet” button.

Within the ensuing “Add Subnet” section, you are required to provide the following granular details:

• Subnet name: Provide a descriptive and functional name for your workload subnet. A name such as “SN-Workload” (signifying “Subnet for Workloads”) is exemplary, offering immediate clarity regarding its intended purpose. Other suitable names might include “AppSubnet” for application servers or “DBSunset” for database instances, depending on your segmentation strategy.
• Subnet address range: Define a suitable and appropriately sized subnet address range that is logically contained within your broader 192.168.0.0/16 spoke VNet address space. For example, 192.168.1.0/24 is a common choice, providing 256 IP addresses (with 5 reserved by Azure for internal services like DHCP, DNS, and future use), which is generally more than ample for a significant number of virtual machines or containerized workloads. The sizing of this subnet should carefully consider the anticipated number of resources, potential for future expansion, and adherence to IP address management best practices. Upon the meticulous input of these parameters, finalize your subnet configuration by initiating a click on “Add.”

To conclude this extensive step, with all network parameters scrupulously defined and validated, proceed by initiating a click on “Review + Create.” This action prompts Azure to conduct its final validation pass, ensuring the coherence and viability of your proposed network architecture. Once the validation process successfully culminates, indicated by the ubiquitous green checkmark, finalize the deployment by initiating a click on “Create.” Similar to the hub VNet deployment, this provisioning phase, encompassing the creation of a virtual network and its designated subnets, might also logically require a few minutes for complete provisioning within the distributed Azure infrastructure. This brief but necessary temporal expenditure is a consequence of Azure orchestrating the global allocation of network resources and establishing the intricate routing tables required for effective communication. Your patience during this crucial interval ensures the robust and error-free instantiation of your spoke network.

Forging Connectivity: Implementing VNet Peering

With both the hub VNet and the spoke VNet meticulously provisioned, the next critical step in establishing a functional and secure network topology is the implementation of Virtual Network Peering. VNet peering is a network mechanism that seamlessly connects two or more Azure Virtual Networks, allowing resources in each VNet to communicate with each other directly using private IP addresses. This connectivity functions as if the resources were part of the same VNet, but without the overhead of complex routing devices. It’s a non-transitive relationship, meaning if VNet A is peered with VNet B, and VNet B is peered with VNet C, VNet A and VNet C cannot communicate directly without a separate peering relationship or a Network Virtual Appliance (NVA) acting as a router. For our hub-and-spoke model, this means we will establish peering between the hub VNet and the spoke VNet.

To configure VNet Peering, navigate back to one of the Virtual Networks you just created in the Azure portal (e.g., “MyHubVNet”). In the left-hand navigation pane for the VNet, locate and select “Peerings” under the “Settings” section. On the Peerings blade, click on “+ Add” to initiate the creation of a new peering connection.

When adding a peering, you will need to define two distinct peering links: one from the current VNet (e.g., MyHubVNet) to the remote VNet (e.g., MySpokeVNet), and another from the remote VNet back to the current VNet. Azure streamlines this by allowing you to configure both sides simultaneously. You’ll specify:

• Peering link name from <current VNet> to <remote VNet>: Provide a descriptive name, such as “HubToSpokePeering.”
• Virtual network deployment model: Select “Resource manager” (the most common and modern deployment model).
• Subscription: Confirm the correct Azure subscription.
• Virtual network: Select your remote VNet (e.g., “MySpokeVNet”).
• Peering link name from <remote VNet> to <current VNet>: Provide a descriptive name, such as “SpokeToHubPeering.”

Crucially, you must also configure the traffic flow permissions for each side of the peering:

• Allow MyHubVNet to access MySpokeVNet: Check “Allow traffic to remote virtual network.”
• Allow MySpokeVNet to access MyHubVNet: Check “Allow traffic to remote virtual network.”
• Allow forwarded traffic: This setting is critical for our hub-and-spoke topology. For the peering from MyHubVNet to MySpokeVNet, uncheck “Allow forwarded traffic from remote virtual network.” For the peering from MySpokeVNet to MyHubVNet, you must check “Allow forwarded traffic from remote virtual network.” This configuration ensures that traffic originating from the spoke, destined for the internet or other spokes, can be routed through the hub VNet, specifically towards the Azure Firewall located within the hub.
• Allow gateway transit: For the peering from MyHubVNet to MySpokeVNet, if you had a VPN or ExpressRoute gateway in the hub VNet that you wanted spokes to use, you would check “Allow gateway transit.” For the peering from MySpokeVNet to MyHubVNet, you would check “Use remote virtual network gateways.” In our current scenario, focusing on Firewall DNAT, this might not be immediately relevant unless you plan to connect on-premises networks later, but it’s an important consideration for a complete hub.
• Virtual network gateway: Leave this as “None” unless you are specifically configuring gateway transit.

Once all parameters are meticulously reviewed, click “Add.” Azure will then proceed to establish the peering connections. This process typically completes within a few moments, and the peering status will change to “Connected” on both sides, signifying successful establishment of direct communication channels between your hub and spoke networks. Proper peering is the arterial system that enables the flow of network traffic towards the centralized security appliance, the Azure Firewall.

Deploying the Sentinel: Instantiating Azure Firewall

With the foundational virtual networks and their inter-connectivity established through peering, the time has arrived to deploy the cornerstone of your network security posture: the Azure Firewall. Azure Firewall is a managed, cloud-native network security service that provides threat protection for your Azure Virtual Network resources. It’s a fully stateful firewall as a service, offering built-in high availability and unrestricted cloud scalability. Deploying it into the dedicated AzureFirewallSubnet within your hub VNet is a critical step towards centralizing your security controls.

To commence the deployment of your Azure Firewall, return to the Azure portal and utilize the omnipresent search bar once more. Input “Azure Firewall” and select the corresponding service from the search results. On the Azure Firewall blade, click “+ Create.”

You will then be presented with the “Create a firewall” configuration page, requiring careful input of the following details:

• Basics Tab:
  • Subscription: Verify the correct Azure subscription.
  • Resource group: Select the same resource group utilized for your hub and spoke VNets. This consistency aids in resource management and policy application.
  • Firewall name: Assign a descriptive and unique name for your firewall (e.g., “MyAzureFirewall”).
  • Region: Select the same region as your hub and spoke VNets to ensure optimal latency and resource locality.
  • Firewall SKU: This is a crucial choice.
    • Standard: Provides core L3-L7 filtering, network rules, application rules, threat intelligence, and basic logging. This is often sufficient for many scenarios.
    • Premium: Offers all Standard features plus advanced threat protection capabilities such as TLS inspection, IDPS (Intrusion Detection and Prevention System), and URL filtering. Choose Premium if your security requirements demand deeper packet inspection and advanced threat protection for encrypted traffic. For the purpose of inbound DNAT, Standard is typically adequate, but Premium offers enhanced security for broader enterprise use.
  • Availability zone: For enhanced resilience and high availability, you can select one or more availability zones. Deploying into multiple zones ensures that your firewall remains operational even if one zone experiences an outage. For production environments, deploying across at least two zones is highly recommended.
• Network Tab:
  • Virtual network: Select your hub VNet (e.g., “MyHubVNet”). The presence of the “AzureFirewallSubnet” within this VNet is what makes it a valid deployment target.
  • Public IP address: You have the option to “Add new” or “Use existing.” For inbound internet traffic filtering and DNAT, a Public IP address is absolutely mandatory as it serves as the internet-facing endpoint for your firewall. Provide a name for the new public IP address (e.g., “MyFirewallPublicIP”). This IP will be the external address to which inbound traffic is directed before being translated and forwarded to internal resources.
  • Force tunneling: This advanced setting allows you to route all internet-bound traffic from Azure to an on-premises firewall via a VPN Gateway or ExpressRoute. For this guide, leave it disabled, as our primary focus is inbound DNAT directly to Azure resources.
• Review + Create: After meticulously filling in all the parameters, click “Review + Create” to validate your configuration. Once validation passes, click “Create.”

The deployment of an Azure Firewall is a resource-intensive operation and typically takes a considerable amount of time, often 10-15 minutes or more, for complete provisioning. During this period, Azure is allocating dedicated resources, configuring the underlying network fabric, and ensuring that the managed service is fully operational and ready to process traffic. Patience is key during this phase; attempting to configure rules or routes before the firewall is fully deployed will result in errors. Once deployed, the firewall’s status will change to “Succeeded,” and you will be able to access its management blade to define rules and monitor its activity. This managed service offloads the operational burden of maintaining a firewall appliance, allowing you to focus purely on defining your security policies.

Sculpting Security: Configuring Azure Firewall Policy DNAT

With the Azure Firewall successfully instantiated within your hub VNet, the pivotal phase of defining its operational directives commences: the configuration of Azure Firewall Policy DNAT (Destination Network Address Translation) rules. Firewall Policy is the modern, recommended approach for managing Azure Firewall rules, offering centralized management, hierarchical rule sets, and integration with Azure Firewall Manager for scaled deployments. DNAT is the mechanism that allows inbound internet traffic, directed to a specific public IP address and port on your firewall, to be translated to a private IP address and port of a resource located within your private Azure Virtual Networks. This effectively exposes an internal service to the internet without directly exposing the internal resource’s private IP.

To configure the DNAT rules, navigate to your deployed Azure Firewall instance in the Azure portal. In the left-hand navigation pane, select “Policies” under the “Settings” section (or directly search for “Firewall Policy” if you are managing policies centrally). If you haven’t already, you will need to create a Firewall Policy associated with your Azure Firewall. Click “Create Firewall Policy” and provide a name (e.g., “MyFirewallPolicy”), select the same resource group and region, and choose the Firewall (e.g., “MyAzureFirewall”) it will manage.

Once the Firewall Policy is created and associated, open its management blade. Within the Firewall Policy, navigate to “DNAT Rule Collection Groups” in the left-hand menu. This is where you organize your DNAT rules. Click “+ Add a rule collection group.”

When adding a DNAT rule collection group, define the following:

• Name: A descriptive name for the group (e.g., “InboundWebServersDNAT”).
• Priority: A numerical value (100-65000) that determines the processing order. Lower values have higher priority. DNAT rules are processed before Network and Application rules.
• Action: For DNAT rules, the action is implicitly “DNAT.”
• Type: Select “DNAT.”

Within this newly created rule collection group, you will then add individual DNAT rules. Click “+ Add rule collection” and then “+ Add rule” within the collection. For each DNAT rule, you must specify:

• Rule name: A unique identifier for the specific rule (e.g., “WebTrafficToVM1”).
• Source type: Typically “IP Address.”
• Source: Define the source IP addresses or CIDR ranges from which inbound traffic is permitted. For general internet access, you might specify “*” (any source) or a more restrictive range if only specific external IPs should reach your service.
• Protocol: Specify the transport protocol (e.g., TCP, UDP, ICMP). For a web server, this would typically be TCP.
• Destination type: Typically “IP Address.”
• Destination Port: The public port on the Azure Firewall’s Public IP address that inbound traffic will hit (e.g., “80” for HTTP, “443” for HTTPS).
• Destination IP Address: This is the public IP address of your Azure Firewall (the one you provisioned during firewall deployment).
• Translated address: The private IP address of the internal Azure resource (e.g., a Virtual Machine’s NIC private IP) to which the inbound traffic will be forwarded after translation (e.g., 192.168.1.4 for a web server VM in the spoke VNet).
• Translated port: The actual port on the internal resource to which the traffic should be forwarded (e.g., “80” or “443”). This can be the same as the destination port or different if you need port remapping.

After defining all the parameters for your DNAT rule, click “Add.” You can add multiple DNAT rules within a collection group, and multiple collection groups within a policy. The prioritization ensures that more specific rules are evaluated before broader ones. Once rules are configured, click “Save” on the policy to apply the changes to your Azure Firewall. This step takes a few moments as the policy is propagated to the firewall instances. Careful consideration of source IPs, protocols, and translated addresses is paramount to ensuring both accessibility for legitimate traffic and robust protection against unauthorized entry. The precise mapping ensures that only intended services are exposed, and only to the necessary extent, significantly reducing the attack surface of your internal network.

Interconnecting Your Networks: Peering the VNets

To establish seamless communication between your hub and spoke VNets, navigate to the Azure portal, search for “Virtual Networks,” and then select “MyHubVNet” (the hub VNet created earlier).

On the “Overview” page of your hub VNet, under “Settings,” select “Subnets.” Click on “+ Subnet.” In the “Add subnet” tab, provide a name for a new subnet (e.g., “GatewaySubnet” if you plan to implement a VPN Gateway later, though not strictly required for this DNAT setup) and click “Add.”

Next, still on the “Overview” page of MyHubVNet, under “Settings,” select “Peerings.” Click on “+ Add.” In the “Add peering” tab, provide the following specific details:

Under “This virtual network”:

• Peering link name: Enter “Peer-HubSpoke.”

Under “Remote virtual network”:

• Peering link name: Enter “Peer-SpokeHub.”
• Virtual network: Select “MySpokeVNet” from the dropdown list.

Finally, click “Add.” You will observe the newly established peering displayed within the “Peerings” tab, signifying a successful interconnection.

Establishing Your Internal Resource: Creating a Virtual Machine

To provide an internal target for your inbound traffic, search for “Virtual machines” in the Azure portal and select “Virtual machines” from the presented results.

On the “Virtual Machines” tab, click “+ Create,” then select “Azure virtual machine.” In the “Create a Virtual Machine” tab, populate the “Basics” tab with the following crucial values:

• Resource group: Select your pre-existing resource group.
• Virtual machine name: Assign a distinctive name (e.g., “MyWorkloadVM”).
• Region: Ensure this matches your VNet regions.
• Image: Choose a suitable operating system image (e.g., “Windows Server 2019 Datacenter”).
• Size: Select an appropriate VM size.
• Username: Provide a valid username for administrative access.
• Password: Set a strong password for the VM.
• Public inbound ports: Select “None” as the firewall will manage access.
• Networking Tab: Ensure the VM is placed in MySpokeVNet and the SN-Workload subnet.

After reviewing the configurations, click “Review + Create” and then “Create.” The deployment of your virtual machine will typically complete within a few minutes.

Deploying Your Security Enforcer: Deploying the Firewall and Policy

To introduce the pivotal security component, in the Azure portal, enter “Firewall” at the top search bar and select “Firewalls” from the subsequent results.

On the “Firewalls” page, click “Create.” In the “Basics” tab of the “Create a Firewall” page, include the following pertinent details:

• Resource group: Select the same resource group.
• Firewall name: Provide a unique name for your firewall (e.g., “MyAzureFirewall”).
• Region: Select the same region as your VNets.
• Firewall management: Choose “Firewall Policy.”
• Firewall policy: Click “Create new” and give it a name (e.g., “MyFirewallPolicy”).
• Virtual network: Select “MyHubVNet” and specify the “AzureFirewallSubnet” that you previously created.
• Public IP address: Create a new public IP address for your firewall.

After careful review, click “Review + Create” and then “Create.” The deployment of your Azure Firewall and its associated policy will be initiated and completed shortly.

Directing Network Flow: Creating a Default Route

To ensure all outbound traffic from your spoke VNet is directed through the Azure Firewall, a default route is necessary. In the Azure portal, navigate to “All services,” and under “Networking,” select “Route tables.”

In the “Route tables” interface, click “+ Create.” On the “Create Route table” page, provide the following details:

• Resource group: Select your existing resource group.
• Region: Select the same region.
• Name: Assign a descriptive name (e.g., “RT-ToFirewall”).

Leave other settings at their default values and click “Review + Create.” Subsequently, click “Create.” Once the route table is provisioned, you need to associate it with the subnet where your workload VM resides. Go back to the route table, under “Settings,” select “Subnets,” and then click “Associate.” Select MySpokeVNet and the SN-Workload subnet, and then click “OK.”

Within this route table, you must add a route. Under “Settings,” select “Routes,” and then click “+ Add.” Configure the route as follows:

• Route name: “DefaultRouteToFirewall”
• Address prefix: 0.0.0.0/0 (This signifies all internet-bound traffic).
• Next hop type: “Virtual appliance”
• Next hop address: Enter the private IP address of your Azure Firewall (you can find this on the firewall’s overview page).

Click “Add” to save the route.

Configuring Your Inbound Access: Configuring a DNAT Rule

Now, the crucial step of configuring the Destination Network Address Translation rule. Navigate to your resource group and select your deployed firewall policy (e.g., “MyFirewallPolicy”).

Under “Settings,” select “DNAT rules” and then click “+ Add a rule collection.” In the “Add a Rule collection” tab, provide the following values:

• Name: Assign a descriptive name for the rule collection (e.g., “InboundWebAccess”).
• Priority: Set a priority number (e.g., 100). Lower numbers indicate higher priority.
• Rule collection group: Select “DefaultDnatRuleCollectionGroup.”

Within the “NAT rule details” section, click “Add rule.”

• Name: Give the specific rule a name (e.g., “RDPtoWorkloadVM”).
• Source type: “IP Address”
• Source: * (for any internet source, though for enhanced security, consider specifying known public IP addresses).
• Protocol: “TCP”
• Destination type: “IP Address”
• Destination IP address: Enter the public IP address of your Azure Firewall.
• Destination Ports: 3389 (Standard RDP port).
• Translated IP address: Enter the private IP address of your “MyWorkloadVM.”
• Translated port: 3389.

Click “Add” for the rule, and then click “Add” again to save the rule collection. This configuration directs all incoming TCP traffic on port 3389 to your firewall’s public IP to the private IP of your virtual machine on port 3389.

Verifying Connectivity: Testing the Firewall

To ascertain the successful implementation of your DNAT rule, you must attempt to connect to your internal virtual machine from an external network. Begin by copying the public IP address of your Azure Firewall.

From your local computer, initiate a Remote Desktop Connection (RDP) client. In the “Computer” field, enter the public IP address of your Azure Firewall. Click “Connect.” If the DNAT rule is correctly configured, you should be prompted to enter the credentials for your “MyWorkloadVM,” indicating a successful redirection of the RDP traffic through the Azure Firewall.

Final Confirmation: Validation Test

Upon the completion of all the aforementioned lab steps, it is imperative to perform a validation test to confirm your progress and the efficacy of your configuration. Locate and click the “Validation button” within your lab environment, or navigate to the designated “Lab Validation” section, to thoroughly verify that all steps have been executed accurately and that the desired inbound traffic filtering is functioning as intended.

Concluding Thoughts

This exposition has meticulously detailed the intricacies of inbound internet traffic and has provided a comprehensive understanding of how to effectively filter it utilizing Azure Firewall policy DNAT. The ability to precisely control and redirect incoming connections is paramount for maintaining a robust security posture within your cloud environment.

For those eager to delve deeper into this critical topic and to apply these theoretical constructs in practical scenarios, I highly advocate for the utilization of exam labs. These meticulously crafted sandboxes offer a secure, isolated, and controlled environment, ideal for hands-on experimentation. They empower you to meticulously refine your skills and garner invaluable real-world insights into the sophisticated management of inbound internet traffic with Azure Firewall policy DNAT. Engaging with these practical environments will solidify your understanding and enhance your proficiency in securing your Azure deployments.