Azure CNI Overlay for Application Gateway for Containers and Application Gateway Ingress Controller
What are Azure CNI Overlay and Application Gateway? Azure CNI Overlay leverages logical network spaces for pod IP assignment management (IPAM). This provides enhanced IP scalability with reduced management responsibilities. Application Gateway for Containers is the latest and most recommended container L7 load-balancing solution. It introduces a new scalable control plane and data plane to address the performance demands and modern workloads being deployed to AKS clusters on Azure. Azure network control plane configures routing between Application Gateway and overlay pods. Why is the feature needed? As businesses increasingly use containerized solutions, managing container networks at scale has become a priority. Within container network management, IP address exhaustion, scalability and application load balancing performance are highly requested and discussed in many forums. Azure CNI Overlay is the default container networking IPAM mode on AKS. In the overlay design, AKS nodes use IPs from Azure virtual network (VNet) IP address range and pods are addressed from an overlay IP address range. The overlay pods can communicate with each other directly via a different routing domain. Overlay IP addresses can be reused across multiple clusters in the same VNet, provisioning a solution for IP exhaustion and increasing IP scale to over 1M. Azure CNI Overlay supporting Application Gateway for Containers provides customers with a more performant, reliable, and scalable container networking solution. Meanwhile, Azure CNI Overlay supporting AGIC provides customers with full feature parity if they choose to upgrade AKS clusters from kubenet to Azure CNI Overlay. Key Benefits High scale with Azure CNI Overlay combined with a high-performance ingress solution Azure CNI Overlay provides direct pod to pod routing with high IP scale using direct azure native routing with no encapsulation overhead. IPs can be reused across clusters in the same VNET allowing customers to conserve IP addresses. Application Gateway for Containers is the latest and most recommended container L7 load-balancing solution. Installing Application Gateway for Containers on AKS clusters with Azure CNI Overlay provides customers with the best solution combination of IP scalability and ingress solution on Azure. Feature parity between kubenet and Azure CNI Overlay With the retirement announcement of kubenet, we expect to see customers upgrade their AKS container networking solution from kubenet to Azure CNI Overlay soon. This feature allows customers to maintain business continuity during the transitioning process. Learn More Read more about Azure CNI Overlay and Application Gateway for Containers. Learn more on how to upgrade AKS clusters’ IPAM to Azure CNI Overlay. Learn more about Azure Kubernetes Service and Application Gateway.Unlock enterprise AI/ML with confidence: Azure Application Gateway as your scalable AI access layer
As enterprises accelerate their adoption of generative AI and machine learning to transform operations, enhance productivity, and deliver smarter customer experiences, Microsoft Azure has emerged as a leading platform for hosting and scaling intelligent applications. With offerings like Azure OpenAI, Azure Machine Learning, and Cognitive Services, organizations are building copilots, virtual agents, recommendation engines, and advanced analytics platforms that push the boundaries of what is possible. However, scaling these applications to serve global users introduces new complexities: latency, traffic bursts, backend rate limits, quota distribution, and regional failovers must all be managed effectively to ensure seamless user experiences and resilient architectures. Azure Application Gateway: The AI access layer Azure Application Gateway plays a foundational role in enabling AI/ML at scale by acting as a high-performance Layer 7 reverse proxy—built to intelligently route, protect, and optimize traffic between clients and AI services. Hundreds of enterprise customers are already using Azure Application Gateway to efficiently manage traffic across diverse Azure-hosted AI/ML models—ensuring uptime, performance, and security at global scale. The AI delivery challenge Inferencing against AI/ML backends is more than connecting to a service. It is about doing so: Reliably: across regions, regardless of load conditions Securely: protecting access from bad actors and abusive patterns Efficiently: minimizing latency and request cost Scalable: handling bursts and high concurrency without errors Observably: with real-time insights, diagnostics, and feedback loops for proactive tuning Key features of Azure Application Gateway for AI traffic Smart request distribution: Path-based and round-robin routing across OpenAI and ML endpoints. Built-in health probes: Automatically bypass unhealthy endpoints Security enforcement: With WAF, TLS offload, and mTLS to protect sensitive AI/ML workloads Unified endpoint: Expose a single endpoint for clients; manage complexity internally. Observability: Full diagnostics, logs, and metrics for traffic and routing visibility. Smart rewrite rules: Append path, or rewrite headers per policy. Horizontal scalability: Easily scale to handle surges in demand by distributing load across multiple regions, instances, or models. SSE and real-time streaming: Optimize connection handling and buffering to enable seamless AI response streaming. Azure Web Application Firewall (WAF) Protections for AI/ML Workloads When deploying AI/ML workloads, especially those exposed via APIs, model endpoints, or interactive web apps, security is as critical as performance. A modern WAF helps protect not just the application, but also the sensitive models, training data, and inference pipelines behind it. Core Protections: SQL injection – Prevents malicious database queries targeting training datasets, metadata stores, or experiment tracking systems. Cross-site scripting (XSS) – Blocks injected scripts that could compromise AI dashboards, model monitoring tools, or annotation platforms. Malformed payloads – Stops corrupted or adversarial crafted inputs designed to break parsing logic or exploit model pre/post-processing pipelines. Bot protections – Bot Protection Rule Set detects & blocks known malicious bot patterns (credential stuffing, password spraying). Block traffic based on request body size, HTTP headers, IP addresses, or geolocation to prevent oversized payloads or region-specific attacks on model APIs. Enforce header requirements to ensure only authorized clients can access model inference or fine-tuning endpoints. Rate limiting based on IP, headers, or user agent to prevent inference overloads, cost spikes, or denial of service against AI models. By integrating these WAF protections, AI/ML workloads can be shielded from both conventional web threats and emerging AI-specific attack vectors, ensuring models remain accurate, reliable, and secure. Architecture Real-world architectures with Azure Application Gateway Industries across sectors rely on Azure Application Gateway to securely expose AI and ML workloads: Healthcare → Protecting patient-facing copilots and clinical decision support tools with HIPAA-compliant routing, private inference endpoints, and strict access control. Finance → Safeguarding trading assistants, fraud-detection APIs, and customer chatbots with enterprise WAF rules, rate limiting, and region-specific compliance. Retail & eCommerce → Defending product recommendation engines, conversational shopping copilots, and personalization APIs from scraping and automated abuse. Manufacturing & industrial IoT → Securing AI-driven quality control, predictive maintenance APIs, and digital twin interfaces with private routing and bot protection. Education → Hosting learning copilots and tutoring assistants safely behind WAF, preventing misuse while scaling access for students and researchers. Public sector & government → Enforcing FIPS-compliant TLS, private routing, and zero-trust controls for citizen services and AI-powered case management. Telecommunications & media → Protecting inference endpoints powering real-time translation, content moderation, and media recommendations at scale. Energy & utilities → Safeguarding smart grid analytics, sustainability dashboards, and AI-powered forecasting models through secure gateway routing. Advanced integrations Position Azure Application Gateway as the secure, scalable network entry point to your AI infrastructure Private-only Azure Application Gateway: Host AI endpoints entirely within virtual networks for secure internal access SSE support: Configure HTTP settings for streaming completions via Server-Sent Events Azure Application Gateway+ Azure Functions: Build adaptive policies that reroute traffic based on usage, cost, or time of day Azure Application Gateway + API management to protect OpenAI workloads What’s next: Adaptive AI gateways Microsoft is evolving Azure Application Gateway into a more intelligent, AI aware platform with capabilities such as: Auto rerouting to healthy endpoints or more cost-efficient models. Dynamic token management directly within Azure Application Gateway to optimize AI inference usage. Integrated feedback loops with Azure Monitor and Log Analytics for real-time performance tuning. The goal is to transform Azure Application Gateway from a traditional traffic manager into an adaptive inference orchestrator one that predicts failures, optimizes operational costs, and safeguards AI workloads from misuse. Conclusion Azure Application Gateway is not just a load balancer—it’s becoming a critical enabler for enterprise-grade AI delivery. Today, it delivers smart routing, security enforcement, adaptive observability, and a compliance-ready architecture, enabling organizations to scale AI confidently while safeguarding performance and cost. Looking ahead, Microsoft’s vision includes future capabilities such as quota resiliency to intelligently manage and balance AI usage limits, auto-rerouting to healthy endpoints or more cost-efficient models, dynamic token management within Azure Application Gateway to optimize inference usage, and integrated feedback loops with Azure Monitor and Log Analytics for real-time performance tuning. Together, these advancements will transform Azure Application Gateway from a traditional traffic manager into an adaptive inference orchestrator capable of anticipating failures, optimizing costs, and protecting AI workloads from misuse. If you’re building with Azure OpenAI, Machine Learning, or Cognitive Services, let Azure Application Gateway be your intelligent command center—anticipating needs, adapting in real time, and orchestrating every interaction so your AI can deliver with precision, security, and limitless scale. For more information, please visit: What is Azure Application Gateway v2? | Microsoft Learn What Is Azure Web Application Firewall on Azure Application Gateway? | Microsoft Learn Azure Application Gateway URL-based content routing overview | Microsoft Learn Using Server-sent events with Application Gateway (Preview) | Microsoft Learn AI Architecture Design - Azure Architecture Center | Microsoft LearnProtect against SharePoint CVE-2025-53770 with Azure Web Application Firewall (WAF)
Summary Microsoft recently disclosed CVE-2025-53770, a critical vulnerability affecting on-premises SharePoint Server versions 2016, 2019, 2010, 2013, and Subscription Edition (SE). The vulnerability allows unauthenticated remote code execution (RCE) by chaining two separate CVEs: CVE-2025-49706 – Authentication Bypass CVE-2025-49704 – Deserialization Vulnerability Microsoft has released security updates for SharePoint Server 2016, 2019, and SE. Versions 2010 and 2013 are out of support and will not receive patches, leaving them exposed. If exploited, this vulnerability could allow an attacker to bypass authentication, extract cryptographic keys, and execute arbitrary C# code on the server. Technical details On-premises SharePoint Servers are enterprise-grade collaboration platforms that organizations install and manage on their own infrastructure, typically in their data centers. The attack chain for CVE-2025-53770 involves the following steps: CVE-2025-49706 – Authentication Bypass The attacker sends a crafted POST request targeting the endpoint:/_layouts/15/ToolPane.aspx?DisplayMode=Edit&a=/ToolPane.aspx with a malicious Referer value:/_layouts/SignOut.aspxThis manipulates SharePoint into trusting the request and its payload. CVE-2025-49704 – Deserialization Vulnerability The attacker then sends a POST request with a serialized spinstall0.aspx payload, designed to extract MachineKey values from web.config. These keys are then used to craft a serialized C# code payload embedded in a valid __VIEWSTATE, which SharePoint trusts and executes. Microsoft guidance We strongly recommend following Microsoft's official mitigation steps outlined in the MSRC blog: Customer guidance for SharePoint vulnerability CVE-2025-53770 | Microsoft Security Response Center See the “How to protect your environment” section for patching guidance, configuration updates, and additional mitigation strategies. Protecting with Azure Web Application Firewall You can create a custom rule to help detect and block suspicious requests matching known indicators of this attack. Example WAF custom rule: Condition 1: URI contains / _layouts/15/ToolPane.aspx or / _layouts/15/spinstall0.aspx Condition 2: Referer header contains / _layouts/SignOut.aspx or / _layouts/15/SignOut.aspx JSON view "customRules": [ { "name": "CVE202553770", "priority": 100, "ruleType": "MatchRule", "action": "Block", "matchConditions": [ { "matchVariables": [ { "variableName": "RequestUri" } ], "operator": "Regex", "negationConditon": false, "matchValues": [ "(?i)/_layouts(?:/\\d+)?/(SignOut|spinstall0|ToolPane)\\.aspx" ], "transforms": [] }, { "matchVariables": [ { "variableName": "RequestHeaders", "selector": "Referer" } ], "operator": "Regex", "negationConditon": false, "matchValues": [ "(?i)/_layouts(?:/\\d+)?/(SignOut|spinstall0|ToolPane)\\.aspx" ], "transforms": [] } ], "skippedManagedRuleSets": [], "state": "Enabled" } ] Next steps Patch immediately: Apply Microsoft’s updates for SharePoint 2016, 2019, and SE. Isolate legacy systems: SharePoint 2010 and 2013 remain vulnerable—consider restricting network access or migrating to supported versions. Deploy WAF protections: Add the custom rule above to monitor and block suspicious traffic targeting vulnerable endpoints. You can find more information about Custom Rules on Azure WAF for Application Gateway here or for Azure Front Door here. For more on Azure WAF, see: Azure Web Application Firewall documentationConnectivity options between Hub-and-Spoke and Azure Virtual WAN
Contents Overview Scenario 1 – Traffic hair-pinning using ExpressRoute Scenario 2 – Build a virtual tunnel (SD-WAN or IPSec) Scenario 3 – vNet Peering and vHub connection coexistence Scenario 4 – Transit virtual network for decentralized vNets Conclusion Bonus Overview This article is going to discuss different options that interconnect the Hub and Spoke networking with Virtual WAN for migrations scenarios. The goal of this article is to expand on additional options that can help customers to migrate to their existing Hub and Spoke topology to Azure Virtual WAN. You can find a comprehensive article Migrate to Azure Virtual WAN to go over several considerations during the migration process. The focus of this article is to focus only on the connectivity to facilitate the migration process. Therefore, it is important to note that the interconnectivity options listed here are intended to be used in the short term to ensure a temporary coexistence between both topologies while the workload on the Spoke vNets with the end goal of disconnecting both environments after migration is completed. This article mainly discusses scenarios with a Virtual WAN Secured Virtual Hub; exceptions are noted where applicable. The setup assumes the use of routing intent and route policies, replacing the previous approach of using route tables to secure Virtual Hubs. For more information, please consult: How to configure Virtual WAN Hub routing intent and routing policies. Scenario 1 – Traffic hair-pinning using ExpressRoute circuits To begin the migration, ensure that the target Virtual WAN Hub (vHub) includes all necessary components. For existing vHubs equipped with Firewalls, SD-WAN, VPN (Point-to-Site or Site-to-Site), confirm that these elements are also present and correctly configured on the target Virtual WAN. Additionally, for any migrated Spoke, an optional vNet peering can be maintained to the original Hub vNet if there are dependencies, such as shared services (DNS, Active Directory, and other services). Make sure that the peering configuration has the option for using remote gateway disabled, because once connected to the vHub, the vNet connection requires using remote gateway to be enabled. On this scenario traffic between Hub and Spoke and Virtual WAN Hub is facilitated using an ExpressRoute circuit that is connected to both environments. When a single circuit is connected to both environments’ routes will be exchanged between both environments, and it will hairpin at the MSEE (Microsoft Enterprise Edge) routers. This scenario is a similar approach used described in the article: Migrate to Azure Virtual WAN. Connectivity flow: Source Destination Data Path Spoke vNet Migrated Spokes vNets 1. vNet Hub Firewall 2. vNet ExpressRoute Gateway 3. MSEE via Hairpin 4. vHub ExpressRoute Gateway 5. vHub Firewall Spoke vNet Branches (VPN/SD-WAN) 1. vNet Hub Firewall 2. vNet SD-WAN NVA or VPN Gateway Spoke vNet On-premises DC 1. vNet Hub Firewall 2. ExpressRoute Gateway 3. ExpressRoute Circuit (MSEE) 4. Provider/Customer Migrated vNet Branches (VPN/SD-WAN) 1. vHub Firewall 2. vHub SD-WAN NVA or VPN Gateway Migrated vNet On-premises DC 1. vNet Hub Firewall 2. vNet ExpressRoute Gateway 3. ExpressRoute Circuit (MSEE) 4. Provider/Customer Note: Connectivity also considers that return traffic follows the same path and components. Pros Traffic stays in the Microsoft Backbone and does not go over the Provider or Customer CPE. Built-in route provided by the Azure Platform (this is configurable, see considerations). Cons Expect high latency. Traffic between VNET Hub and vHubs crosses MSEE routers outside the Azure Region in a Cloud Exchange facility, increasing latency due to the distance to the region. Single point of failure. Because the MSEE is located at the Edge location, an outage at that site can impact communication. To ensure redundancy, you can utilize a second MSEE at a different Edge location within the same metro area to achieve redundancy and lower latency. Additionally, a second MSEE in different metro areas can also provide redundancy, although this might result in increased latency. Considerations A new feature has been introduced to block MSEE hairpin. To enable this scenario, you need to activate Allow Traffic from remote Virtual WAN Networks (on VNET Hub side) and Allow Traffic from non-Virtual WAN Networks (on Virtual WAN Hub side). For more details, refer to this article: Customisation controls for connectivity between Virtual Networks over ExpressRoute.. Scenario 2 – Build a virtual tunnel (SD-WAN or IPSec) The same prerequisites for the target vHub apply for this option before beginning the migration. However, instead of utilizing ExpressRoute transit, in this scenario you establish a direct virtual tunnel between the existing VNET Hub and the vHub to facilitate communication. There are several options for achieving this, including: Use Azure native VPN Gateway on both VNET Hub and vHub for IPSec tunnels. Up to four tunnels can be created when VNET Hub VPN Gateway is configured to Active/Active (by default, vHub VPN Gateways are already Active/Active). It is important to consider that customers can use either BGP or static routing when implementing this option. However, BGP will be restricted, if the VNET VPN Gateway is the only gateway present, you can use custom ASN other than 65515. If there is another gateway, such as ExpressRoute or Azure Route Server, ASN must be set to 65515. Since vHub VPN Gateway does not allow custom ASN at this moment (65515 is the default ASN), static routes will be required for this setup. Use 3 rd party NVA to establish SD-WAN connectivity between both sides or IPSec tunnel. Using this option, you can leverage either static or BGP routing, where BGP will offer better integration with vHub and less administrative effort. Connectivity flow: Source Destination Data Path Spoke vNet Migrated Spokes vNets 1. vNet Hub Firewall 2. vNet Hub SD-WAN NVA or VPN Gateway 3. vHub Hub SD-WAN NVA or VPN Gateway 4. vHub Firewall Spoke vNet Branches (VPN/SD-WAN) 1. vNet Hub Firewall 2. vNet Hub SD-WAN NVA or VPN Gateway Spoke vNet On-premises DC 1. vNet Hub Firewall 2. ExpressRoute Gateway 3. MSEE Hairpin 4. Provider/Customer Migrated vNet Branches (VPN/SD-WAN) 1. vHub Firewall 2. SD-WAN NVA or VPN Gateway Migrated vNet On-premises DC 1. vNet Hub Firewall 2. ExpressRoute Gateway 3. MSEE Hairpin 4. Provider/Customer Note: Connectivity also considers that return traffic follows the same path and components. Pros Traffic remains within the Microsoft Backbone in the region, resulting in lower latency compared to Option 1. Cons Administrative overhead when using static routes and managing extra network components. Cost of adding a new VPN Gateway or 3 rd party NVA to build the virtual tunnel Throughput may be limited based on the type of virtual tunnel technology used. This limitation can be mitigated by adding multiple tunnels, which require BGP + ECMP to balance traffic between them. It is important to note that Azure allows up to eight tunnels, which is the maximum number of programmed routes for the same networks with different next hops, indicating the specific tunnel. Scenario 3 – vNet Peering and vHub connection coexistence In this scenario, spokes vNet originally connected to vNet Hub are migrated to the vHub while maintaining existing peering with the vNet Hub but with the Use Remote Gateway configuration disabled. This allows the migrated vNets to retain connectivity with the source vNet Hub while also connecting to the vHub. The connection to the vHub necessitates the Use Remote Gateway, which directs all traffic towards on-premises to use the vHub. To connect with other spokes via vHub, the migrated vNet needs a UDR with routes to the vNet spoke prefixes using the vNet Hub Firewall as the next hop. Use route summarization for contiguous prefixes or enter specific prefixes if they are not. Additionally, enable Gateway Propagation in the UDR so migrated Spoke vNets can learn routes from the vHub (RFC 1918, default route, or both). Connectivity flow: Source Destination Data Path Spoke vNet Migrated Spokes vNet 1. vNet Hub Firewall Spoke vNet Branches (VPN/SD-WAN) 1. vNet Hub Firewall 2. vNet SD-WAN NVA or VPN Gateway Spoke vNet On-premises DC 1. vNet Hub Firewall 2. ExpressRoute Gateway 3. ExpressRoute Circuit (MSEE) 4. Provider/Customer Migrated vNet Branches (VPN/SD-WAN) 1. vHub Firewall 2. vHub SD-WAN NVA or VPN Gateway Migrated vNet On-premises DC 1. vHub Firewall 2. vHub ExpressRoute Gateway 3. ExpressRoute Circuit (MSEE) 4. Provider/Customer Note: Connectivity means that return traffic follows the same path and components. Pros Traffic remains within the Microsoft Backbone in the region, resulting in lower latency compared to option 1. No throughput limitation imposed by virtual tunnels compared to option 2. Throughput will be limited by the VM size. Cons Administrative overhead to adjust the UDR to reach the Spoke vNets on connected over the vNet Hub. Scenario 4 – Transit virtual network for decentralized vNets This use case involves a decentralized virtual network model where each customer has an ExpressRoute Gateway for connectivity to on-premises systems. Traffic between virtual networks is managed using virtual network peering, based on the specific connectivity requirements of the customer. Each virtual network has its own gateway, which prevents connecting them directly to the virtual hub because the remote gateway option needs to be enabled. If the customer can tolerate the downtime associated with removing the Express Route Gateway from the migrated vNet, they have the option to establish a direct vNet connection to the vHub, thereby simplifying the solution. This process typically takes approximately 45 minutes, excluding the rollback procedure which would require an additional 45 minutes, potentially making this approach prohibitive for most customers. However, customers with existing Azure workloads often aim to minimize downtime. As illustrated in the diagram below, they can create a transit vNet equipped with a firewall or a Network Virtual Appliance (NVA) with routing capabilities. This configuration allows the migrated vNet to establish regular peering, thereby maintaining connectivity without significant disruption. The solution illustrated on this section uses a static route propagation at the vNet connection level towards the Transit vNet, which now requires non Secured-Virtual WAN hubs (note that support for static route propagation is on the Virtual WAN roadmap). Alternatively, you can use BGP peering from the Firewall or NVA to program the migrated vNets summary prefixes. For Firewall implementations with BGP it is recommended to leverage Next hop IP support for Virtual WAN where traffic flows over a load balance feature to ensure traffic symmetry. In that scenario you can also leverage Secured-vHubs. The migration process also necessitates adjustments to the routes for the migrated vNET to facilitate traffic flow to on-premises systems using the vHUB. This includes utilizing static routes at the connection from the Transit vNet to the vHub to advertise a summary route via the Firewall in the transit vNET to ensure return traffic and proper advertisement to the on-premises environment. Once the route configurations are established, the ExpressRoute connection can be removed. The customer can then proceed to Step 2, which will allow them to make the final adjustments and complete the full integration with the vHub following the outlined steps. Remove ExpressRoute Gateway. Create the vNet connection to the vHub, that will allow the specific Migrated vNet prefix to advertise to the vHub as well as leak down to the ExpressRoute. Once the step 2 is completed the traffic should start to flow over the vNET connection to the Vub. Removed the vNet peering to the Transit vNET. Connectivity flow: Source Destination Data Path vNet1/VNet2 Migrated Spokes vNet 1. Direct vNet peering vNet1/VNet2 Branches (VPN/SD-WAN) 1. ExpressRoute Gateway 2. ExpressRoute Circuit (MSEE) 3. Provider/Customer 4. VPN/SD-WAN vNet1/VNet2 On-premises DC 1. ExpressRoute Gateway 2. ExpressRoute Circuit (MSEE) 3. Provider/Customer Migrated vNet (Step1) Branches (VPN/SD-WAN) 1. Transit Firewall 2. vHub SD-WAN NVA or VPN Gateway Migrated vNet (Step1) On-premises DC 1. Transit Firewall 2. vHub ExpressRoute Gateway 3. ExpressRoute Circuit (MSEE) 4. Provider/Customer Migrated vNet (Step2) Branches (VPN/SD-WAN) 1. vHub SD-WAN NVA or VPN Gateway Migrated vNet (Step2) On-premises DC 1. vHub ExpressRoute Gateway 2. ExpressRoute Circuit (MSEE) 3. Provider/Customer Note: Connectivity means that return traffic follows the same path and components. Pros Traffic remains on the Microsoft backbone, ensuring minimal latency. Not the same throughput limits associated with option 2 solution (virtual tunnels). Cons Administrative overhead associated with maintaining the additional transit virtual network, including user-defined route management and vHub vNet Connection static route configuration. Costs incurred from operating any supplementary firewalls (FWs) or network virtual appliances (NVAs) in the transit vNet. Conclusion This article outlined four strategies for migrating from Hub and Spoke networking to Azure Virtual WAN—ExpressRoute hair pinning, VPN or SD-WAN virtual tunnels, vNet peering with vHub connections, and transit virtual networks for decentralized vNets—highlighting their pros, cons, and administrative considerations. It is important to assess which approach best fits your needs by weighing each scenario's advantages and drawbacks. Bonus The diagrams in Excalidraw format related to this blog post are available in the following GitHub repository.Network Redundancy Between AVS, On-Premises, and Virtual Networks in a Multi-Region Design
By Mays_Algebary shruthi_nair Establishing redundant network connectivity is vital to ensuring the availability, reliability, and performance of workloads operating in hybrid and cloud environments. Proper planning and implementation of network redundancy are key to achieving high availability and sustaining operational continuity. This article focuses on network redundancy in multi-region architecture. For details on single-region design, refer to this blog. The diagram below illustrates a common network design pattern for multi-region deployments, using either a Hub-and-Spoke or Azure Virtual WAN (vWAN) topology, and serves as the baseline for establishing redundant connectivity throughout this article. In each region, the Hub or Virtual Hub (VHub) extends Azure connectivity to Azure VMware Solution (AVS) via an ExpressRoute circuit. The regional Hub/VHub is connected to on-premises environments by cross-connecting (bowtie) both local and remote ExpressRoute circuits, ensuring redundancy. The concept of weight, used to influence traffic routing preferences, will be discussed in the next section. The diagram below illustrates the traffic flow when both circuits are up and running. Design Considerations If a region loses its local ExpressRoute connection, AVS in that region will lose connectivity to the on-premises environment. However, VNets will still retain connectivity to on-premises via the remote region’s ExpressRoute circuit. The solutions discussed in this article aim to ensure redundancy for both AVS and VNets. Looking at the diagram above, you might wonder: why do we need to set weights at all, and why do the AVS-ER connections (1b/2b) use the same weight as the primary on-premises connections (1a/2a)? Weight is used to influence routing decisions and ensure optimal traffic flow. In this scenario, both ExpressRoute circuits, ER1-EastUS and ER2-WestUS, advertise the same prefixes to the Azure ExpressRoute gateway. As a result, traffic from the VNet to on-premises would be ECMPed across both circuits. To avoid suboptimal routing and ensure that traffic from the VNets prefers the local ExpressRoute circuit, a higher weight is assigned to the local path. It’s also critical that the ExpressRoute gateway connection to on-premises (1a/2a) and to AVS (1b/2b), is assigned the same weight. Otherwise, traffic from the VNet to AVS will follow a less efficient route as AVS routes are also learned over ER1-EastUS via Global Reach. For instance, VNets in EastUS will connect to AVS EUS through ER1-EastUS circuit via Global Reach (as shown by the blue dotted line), instead of using the direct local path (orange line). This suboptimal routing is illustrated in the below diagram. Now let us see what solutions we can have to achieve redundant connectivity. The following solutions will apply to both Hub-and-Spoke and vWAN topology unless noted otherwise. Note: The diagrams in the upcoming solutions will focus only on illustrating the failover traffic flow. Solution1: Network Redundancy via ExpressRoute in Different Peering Location In the solution, deploy an additional ExpressRoute circuit in a different peering location within the same metro area (e.g., ER2–PeeringLocation2), and enable Global Reach between this new circuit and the existing AVS ExpressRoute (e.g., AVS-ER1). If you intend to use this second circuit as a failover path, apply prepends to the on-premises prefixes advertised over it. Alternatively, if you want to use it as an active-active redundant path, do not prepend routes, in this case, both AVS and Azure VNets will ECMP to distribute traffic across both circuits (e.g., ER1–EastUS and ER–PeeringLocation2) when both are available. Note: Compared to the Standard Topology, this design removes both the ExpressRoute cross-connect (bowtie) and weight settings. When adding a second circuit in the same metro, there's no benefit in keeping them, otherwise traffic from the Azure VNet will prefer the local AVS circuit (AVS-ER1/AVS-ER2) to reach on-premises due to the higher weight, as on-premises routes are also learned over AVS circuit (AVS-ER1/AVS-ER2) via Global Reach. Also, when connecting the new circuit (e.g., ER–Peering Location2), remove all weight settings across the connections. Traffic will follow the optimal path based on BGP prepending on the new circuit, or load-balance (ECMP) if no prepend is applied. Note: Use public ASN to prepend the on-premises prefix as AVS circuit (e.g., AVS-ER) will strip the private ASN toward AVS. Solution Insights Ideal for mission-critical applications, providing predictable throughput and bandwidth for backup. It could be cost prohibitive depending on the bandwidth of the second circuit. Solution2: Network Redundancy via ExpressRoute Direct In this solution, ExpressRoute Direct is used to provision multiple circuits from a single port pair in each region, for example, ER2-WestUS and ER4-WestUS are created from the same port pair. This allows you to dedicate one circuit for local traffic and another for failover to a remote region. To ensure optimal routing, prepend the on-premises prefixes using public ASN on the newly created circuit (e.g., ER3-EastUS and ER4-WestUS). Remove all weight settings across the connections; traffic will follow the optimal path based on BGP prepending on the new circuit. For instance, if ER1-EastUS becomes unavailable, traffic from AVS and VNets in the EastUS region will automatically route through ER4-WestUS circuit, ensuring continuity. Note: Compared to the Standard Topology, this design connects the newly created ExpressRoute circuits (e.g., ER3-EastUS/ER4-WestUS) to the remote region of ExpressRoute gateway (black dotted lines) instead of having the bowtie to the primary circuits (e.g., ER1-EastUS/ER2-WestUS). Solution Insights Easy to implement if you have ExpressRoute Direct. ExpressRoute Direct supports over- provisioning where you can create logical ExpressRoute circuits on top of your existing ExpressRoute Direct resource of 10-Gbps or 100-Gbps up to the subscribed Bandwidth of 20 Gbps or 200 Gbps. For example, you can create two 10-Gbps ExpressRoute circuits within a single 10-Gbps ExpressRoute Direct resource (port pair). Ideal for mission-critical applications, providing predictable throughput and bandwidth for backup. Solution3: Network Redundancy via ExpressRoute Metro Metro ExpressRoute is a new configuration that enables dual-homed connectivity to two different peering locations within the same city. This setup enhances resiliency by allowing traffic to continue flowing even if one peering location goes down, using the same circuit. Solution Insights Higher Resiliency: Provides increased reliability with a single circuit. Limited regional availability: Currently available in select regions, with more being added over time. Cost-effective: Offers redundancy without significantly increasing costs. Solution4: Deploy VPN as a Backup to ExpressRoute This solution mirrors solution 1 for a single region but extends it to multiple regions. In this approach, a VPN serves as the backup path for each region in the event of an ExpressRoute failure. In a Hub-and-Spoke topology, a backup path to and from AVS can be established by deploying Azure Route Server (ARS) in the hub VNet. ARS enables seamless transit routing between ExpressRoute and the VPN gateway. In vWAN topology, ARS is not required; the vHub's built-in routing service automatically provides transitive routing between the VPN gateway and ExpressRoute. In this design, you should not cross-connect ExpressRoute circuits (e.g., ER1-EastUS and ER2-WestUS) to the ExpressRoute gateways in the Hub VNets (e.g., Hub-EUS or Hub-WUS). Doing so will lead to routing issues, where the Hub VNet only programs the on-premises routes learned via ExpressRoute. For instance, in the EastUS region, if the primary circuit (ER1-EastUS) goes down, Hub-EUS will receive on-premises routes from both the VPN tunnel and the remote ER2-WestUS circuit. However, it will prefer and program only the ExpressRoute-learned routes from ER2-WestUS circuit. Since ExpressRoute gateways do not support route transitivity between circuits, AVS connected via AVS-ER will not receive the on-premises prefixes, resulting in routing failures. Note: In vWAN topology, to ensure optimal route convergence when failing back to ExpressRoute, you should prepend the prefixes advertised from on-premises over the VPN. Without route prepending, VNets may continue to use the VPN as the primary path to on-premises. If prepend is not an option, you can trigger the failover manually by bouncing the VPN tunnel. Solution Insights Cost-effective and straightforward to deploy. Increased Latency: The VPN tunnel over the internet adds latency due to encryption overhead. Bandwidth Considerations: Multiple VPN tunnels might be needed to achieve bandwidth comparable to a high-capacity ExpressRoute circuit (e.g., over 1G). For details on VPN gateway SKU and tunnel throughput, refer to this link. As you can't cross connect ExpressRoute circuits, VNets will utilize the VPN for failover instead of leveraging remote region ExpressRoute circuit. Solution5: Network Redundancy-Multiple On-Premises (split-prefix) In many scenarios, customers advertise the same prefix from multiple on-premises locations to Azure. However, if the customer can split prefixes across different on-premises sites, it simplifies the implementation of failover strategy using existing ExpressRoute circuits. In this design, each on-premises advertises region-specific prefixes (e.g., 10.10.0.0/16 for EastUS and 10.70.0.0/16 for WestUS), along with a common supernet (e.g., 10.0.0.0/8). Under normal conditions, AVS and VNets in each region use longest prefix match to route traffic efficiently to the appropriate on-premises location. For instance, if ER1-EastUS becomes unavailable, AVS and VNets in EastUS will automatically fail over to ER2-WestUS, routing traffic via the supernet prefix to maintain connectivity. Solution Insights Cost-effective: no additional deployment, using existing ExpressRoute circuits. Advertising specific prefixes over each region might need additional planning. Ideal for mission-critical applications, providing predictable throughput and bandwidth for backup. Solution6: Prioritize Network Redundancy for One Region Over Another If you're operating under budget constraints and can prioritize one region (such as hosting critical workloads in a single location) and want to continue using your existing ExpressRoute setup, this solution could be an ideal fit. In this design, assume AVS in EastUS (AVS-EUS) hosts the critical workloads. To ensure high availability, AVS-ER1 is configured with Global Reach connections to both the local ExpressRoute circuit (ER1-EastUS) and the remote circuit (ER2-WestUS). Make sure to prepend the on-premises prefixes advertised to ER2-WestUS using public ASN to ensure optimal routing (no ECMP) from AVS-EUS over both circuits (ER1-EastUS and ER2-WestUS). On the other hand, AVS in WestUS (AVS-WUS) is connected via Global Reach only to its local region ExpressRoute circuit (ER2-WestUS). If that circuit becomes unavailable, you can establish an on-demand Global Reach connection to ER1-EastUS, either manually or through automation (e.g., a triggered script). This approach introduces temporary downtime until the Global Reach link is established. You might be thinking, why not set up Global Reach between the AVS-WUS circuit and remote region circuits (like connecting AVS-ER2 to ER1-EastUS), just like we did for AVS-EUS? Because it would lead to suboptimal routing. Due to AS path prepending on ER2-WestUS, if both ER1-EastUS and ER2-WestUS are linked to AVS-ER2, traffic would favor the remote ER1-EastUS circuit since it presents a shorter AS path. As a result, traffic would bypass the local ER2-WestUS circuit, causing inefficient routing. That is why for AVS-WUS, it's better to use on-demand Global Reach to ER1-EastUS as a backup path, enabled manually or via automation, only when ER2-WestUS becomes unavailable. Note: VNets will failover via local AVS circuit. E.g., HUB-EUS will route to on-prem through AVS-ER1 and ER2-WestUS via Global Reach Secondary (purple line). Solution Insights Cost-effective Workloads hosted in AVS within the non-critical region will experience downtime if the local region ExpressRoute circuit becomes unavailable, until the on-demand Global Reach connection is established. Conclusion Each solution has its own advantages and considerations, such as cost-effectiveness, ease of implementation, and increased resiliency. By carefully planning and implementing these solutions, organizations can ensure operational continuity and optimal traffic routing in multi-region deployments.
DNS best practices for implementation in Azure Landing Zones
Why DNS architecture matters in Landing Zone A well-designed DNS layer is the glue that lets workloads in disparate subscriptions discover one another quickly and securely. Getting it right during your Azure Landing Zone rollout avoids painful refactoring later, especially once you start enforcing Zero-Trust and hub-and-spoke network patterns. Typical Landing-Zone topology Subscription Typical Role Key Resources Connectivity (Hub) Transit, routing, shared security Hub VNet, Azure Firewall / NVA, VPN/ER gateways, Private DNS Resolver Security Security tooling & SOC Sentinel, Defender, Key Vault (HSM) Shared Services Org-wide shared apps ADO and Agents, Automation Management Ops & governance Log Analytics, backup etc Identity Directory and auth services Extended domain controllers, Azure AD DS All five subscriptions contain a single VNet. Spokes (Security, Shared, Management, Identity) are peered to the Connectivity VNet, forming the classic hub-and-spoke. Centralized DNS with mandatory firewall inspection Objective: All network communication from a spoke must cross the firewall in the hub including DNS communication. Design Element Best-Practice Configuration Private DNS Zones Link only to the Connectivity VNet. Spokes have no direct zone links. Private DNS Resolver Deploy inbound + outbound endpoints in the Connectivity VNet. Link connectivity virtual network to outbound resolver endpoint. Spoke DNS Settings Set custom DNS servers on each spoke VNet equal to the inbound endpoint’s IPs. Forwarding Ruleset Create a ruleset, associate it with the outbound endpoint, and add forwarders: • Specific domains → on-prem / external servers • Wildcard “.” → on-prem DNS (for compliance scenarios) Firewall Rules Allow UDP/TCP 53 from spokes to Resolver-inbound, and from Resolver-outbound to target DNS servers Note: Azure private DNS zone is a global resource. Meaning single private DNS zone can be utilized to resolve DNS query for resources deployed in multiple regions. DNS private resolver is a regional resource. Meaning it can only link to virtual network within the same region. Traffic flow Spoke VM → Inbound endpoint (hub) Firewall receives the packet based on spoke UDR configuration and processes the packet before it sent to inbound endpoint IP. Resolver applies forwarding rules on unresolved DNS queries; unresolved queries leave via Outbound endpoint. DNS forwarding rulesets provide a way to route queries for specific DNS namespaces to designated custom DNS servers. Fallback to internet and NXDOMAIN redirect Azure Private DNS now supports two powerful features to enhance name resolution flexibility in hybrid and multi-tenant environments: Fallback to internet Purpose: Allows Azure to resolve DNS queries using public DNS if no matching record is found in the private DNS zone. Use case: Ideal when your private DNS zone doesn't contain all possible hostnames (e.g., partial zone coverage or phased migrations). How to enable: Go to Azure private DNS zones -> Select zone -> Virtual network link -> Edit option Ref article: https://learn.microsoft.com/en-us/azure/dns/private-dns-fallback Centralized DNS - when firewall inspection isn’t required Objective: DNS query is not monitored via firewall and DNS query can be bypassed from firewall. Link every spoke virtual directly to the required Private DNS Zones so that spoken can resolve PaaS resources directly. Keep a single Private DNS Resolver (optional) for on-prem name resolution; spokes can reach its inbound endpoint privately or via VNet peering. Spoke-level custom DNS This can point to extended domain controllers placed within identity virtual. This pattern reduces latency and cost but still centralizes zone management. Integrating on-premises active directory DNS Create conditional forwarders on each Domain Controller for every Private DNS Zone pointing it to DNS private resolver inbound endpoint IP Address. (e.g.,blob.core.windows.net database.windows.net). Do not include the literal privatelink label. Ref article: https://github.com/dmauser/PrivateLink/tree/master/DNS-Integration-Scenarios#43-on-premises-dns-server-conditional-forwarder-considerations Note: Avoid selecting the option “Store this conditional forwarder in Active Directory and replicate as follows” in environments with multiple Azure subscriptions and domain controllers deployed across different Azure environments. Key takeaways Linking zones exclusively to the connectivity subscription's virtual network keeps firewall inspection and egress control simple. Private DNS Resolver plus forwarding rulesets let you shape hybrid name resolution without custom appliances. When no inspection is needed, direct zone links to spokes cut hops and complexity. For on-prem AD DNS, the conditional forwarder is required pointing it to inbound endpoint IP, exclude privatelink name when creating conditional forwarder, and do not replicate conditional forwarder Zone with AD replication if customer has footprint in multiple Azure tenants. Plan your DNS early, bake it into your infrastructure-as-code, and your landing zone will scale cleanly no matter how many spokes join the hub tomorrow.Optimize Azure Firewall logs with selective logging
A common question from customers is whether Azure Firewall supports filtering or selecting which logs are sent to a Log Analytics workspace. This concern usually stems from the high cost of storing large volumes of data — especially in environments where the firewall inspects substantial amounts of network traffic. Azure Firewall now supports ingestion-time transformation of logs in Azure Log Analytics. This capability introduces selective and advanced filtering, giving customers more control over what data is collected and analyzed. In this blog post, we’ll explore a major new capability: Azure Firewall now supports ingestion-time transformations in Log Analytics — enabling flexible, cost-efficient logging through selective data collection. Why does it matter? For many enterprise customers, the cost of ingesting Azure Firewall logs into Log Analytics — especially at scale — can be significant. Depending on the logging mode (Basic or Analytics), ingestion costs can be substantial, potentially making it challenging to expand logging coverage across additional workloads. With ingestion-time transformations, users can filter logs by rows, columns, timestamps, and more — and apply transformations before ingestion. This ensures that only relevant and critical data is stored, helping reduce costs while retaining the necessary telemetry for analysis, threat detection, and compliance. Customer benefits Security monitoring: Log only suspicious traffic for more targeted threat detection. Cost optimization: Avoid ingesting and storing unnecessary data. Compliance: Use DCR (data collection rules) to filter and route logs to meet audit/reporting needs. Incident response: Focus on logs that matter, accelerating investigation time. Custom alerts: Build insights on top of curated, high-value logs. What are transformations in Azure Monitor? Ingestion-time transformations in Azure Monitor allow you to filter or modify incoming telemetry before it reaches your Log Analytics workspace. This happens in the cloud pipeline — after the data source (such as Azure Firewall) sends its logs, but before those logs are ingested and stored. Transformations are defined using DCR and written in Kusto Query Language (KQL). Each transformation runs against incoming records individually, letting you precisely control what gets stored – and what doesn’t. For example, you might collect only entries where the action column contains the word “deny”. That filter can be applied at ingestion time, so only those critical logs are stored. The diagram below shows how this works end-to-end, from data source to filtered ingestion. To learn more and estimate potential processing charges, refer to the official documentation. Transforming Azure Firewall logging In this section, we’ll walk through a few real-world use cases shared by customers — including how to create a DCR based on specific filtering criteria. Important: Ingestion-time transformations for Azure Firewall logs are supported only when using resource-specific logs. If you’re using legacy diagnostic settings, this capability is not available. To enable transformations, ensure your firewall is configured to send logs using the Azure Firewall resource-specific log schema. First, navigate to your Log Analytics workspace and locate the table where your Azure Firewall logs are stored (e.g., AZFWApplicationRule). Click the three-dot menu (…) on the right and select “Create transformation”. Creating a transformation is a 3 steps-process. Step 1 – Basics: Create a DCR to define how incoming data is processed and specify where it should be stored. Step 2 – Schema and transformation: Use the Transformation Editor to write a KQL query that filters the incoming data based on your criteria. Step 3 – Review: Review the table name, DCR name, and KQL query before clicking “Create”. This summary ensures everything is configured correctly. For more information on how to create a DCR, refer to the official documentation. Use case 1: Excluding alerts from low priority IDPS signatures This DCR transformation filters and reshapes incoming Azure Firewall IDPS logs before they're ingested into a Log Analytics workspace. source | where Action !contains "alert" and Severity != 3 | project TimeGenerated, Protocol, SourceIp, SourcePort, DestinationIp, DestinationPort, Action, SignatureId, Description, Severity Here's a breakdown of what it does: source: This refers to the incoming data stream — in this case, the AZFWIdpsSignature table (intrusion detection/prevention logs from Azure Firewall). | where Action !contains "alert" and Severity != 3: This line filters out any log entries where the Action contains "alert" (non-blocking detection events). Any entries where Severity equals 3 (which represents low severity events). The result: We’re keeping only more actionable or higher-severity entries that don’t just raise alerts but may involve blocks or higher-severity behaviors (e.g., deny actions, critical or warning severities). | project ...: The project statement selects and forwards only the specified columns to the Log Analytics workspace. When you run a query in your Log Analytics workspace, you’ll notice that only the specific columns defined in your transformation’s project statement are available — and they appear in the exact order specified in the query. Use case 2: Filtering out unnecessary logs (trusted or testing networks) This DCR transformation filters out log entries from specific source IP address ranges before they're ingested into Azure Monitor. In this scenario, the 10.0.200.x and 10.0.300.x ranges might represent trusted or test network segments that generate high volumes of traffic — traffic that don’t need to be logged. By excluding these IPs at ingestion time, you can significantly reduce unnecessary log volume and associated costs. source | where not( SourceIp startswith "10.0.200." or SourceIp startswith "10.0.300." ) | project TimeGenerated, Protocol, SourceIp, SourcePort, DestinationIp, DestinationPort, Action, ActionReason, Policy, RuleCollection, Rule Here's a breakdown of what it does: source: This refers to the incoming data stream — in this case, the AZFWNetworkRule table. | where not (…): Applies a filter to exclude logs that match the criteria inside. SourceIp startswith "10.0.200." and SourceIp startswith "10.0.300.": These conditions match any log where the SourceIp address falls within the 10.0.200.0/24 or 10.0.300.0/24 subnets (i.e., IPs like 10.0.200.1, 10.0.200.45, etc.). | project ...: The project statement selects and forwards only the specified columns to the Log Analytics workspace. Conclusion By leveraging ingestion-time transformations through DCR, organizations gain full control over which Azure Firewall logs are ingested in Log Analytics. This selective logging capability helps reduce noise, cut costs, and retain only high-value data for security, compliance, and operational insights. As Azure Firewall evolves these enhancements offer greater flexibility and efficiency for managing cloud-native network telemetry. Resources Azure updates | Microsoft Azure Monitoring data reference for Azure Firewall | Microsoft Learn Transformations Azure Monitor - Azure Monitor | Microsoft Learn Create a transformation in Azure Monitor - Azure Monitor | Microsoft Learn
Azure ExpressRoute Direct: A Comprehensive Overview
What is Express Route Azure ExpressRoute allows you to extend your on-premises network into the Microsoft cloud over a private connection made possible through a connectivity provider. With ExpressRoute, you can establish connections to Microsoft cloud services, such as Microsoft Azure, and Microsoft 365. ExpressRoute allows you to create a connection between your on-premises network and the Microsoft cloud in four different ways, CloudExchange Colocation, Point-to-point Ethernet Connection, Any-to-any (IPVPN) Connection, and ExpressRoute Direct. ExpressRoute Direct gives you the ability to connect directly into the Microsoft global network at peering locations strategically distributed around the world. ExpressRoute Direct provides dual 100-Gbps or 10-Gbps connectivity that supports active-active connectivity at scale. Why ExpressRoute Direct Is Becoming the Preferred Choice for Customers ExpressRoute Direct with ExpressRoute Local – Free Egress: ExpressRoute Direct includes ExpressRoute Local, which allows private connectivity to Azure services within the same metro or peering location. This setup is particularly cost-effective because egress (outbound) data transfer is free, regardless of whether you're on a metered or unlimited data plan. By avoiding Microsoft's global backbone, ExpressRoute Local offers high-speed, low-latency connections for regionally co-located workloads without incurring additional data transfer charges. Dual Port Architecture Both ExpressRoute Direct and the service provider model feature a dual-port architecture, with two physical fiber pairs connected to separate Microsoft router ports and configured in an active/active BGP setup that distributes traffic across both links simultaneously for redundancy and improved throughput. What sets Microsoft apart is making this level of resiliency standard, not optional. Forward-thinking customers in regions like Sydney take it even further by deploying ExpressRoute Direct across multiple colocation facilities for example, placing one port pair in Equinix SY2 and another in NextDC S1 creating four connections across two geographically separate sites. This design protects against facility-level outages from power failures, natural disasters, or accidental infrastructure damage, ensuring business continuity for organizations where downtime is simply not an option. When Geography Limits Your Options: Not every region offers facility diversity, example New Zealand has only one ExpressRoute peering location, businesses needing geographic redundancy must connect to Sydney incurring Auckland to Sydney link costs but gaining critical diversity to mitigate outages. While ExpressRoute’s dual ports provide active/active redundancy, both are on the same Microsoft edge, so true disaster recovery requires using Sydney’s edge. ExpressRoute Direct scales from basic dual-port setups to multi-facility deployments and offers another advantage: free data transfer within the same geopolitical region. Once traffic enters Microsoft’s network, New Zealand customers can move data between Azure services across the trans-Tasman link without per-GB fees, with Microsoft absorbing those costs. Premium SKU: Global Reach: Azure ExpressRoute Direct with the Premium SKU enables Global Reach, allowing private connectivity between your on-premises networks across different geographic regions through Microsoft's global backbone. This means you can link ExpressRoute circuits in different countries or continents, facilitating secure and high-performance data exchange between global offices or data centers. The Premium SKU extends the capabilities of ExpressRoute Direct by supporting cross-region connectivity, increased route limits, and access to more Azure regions, making it ideal for multinational enterprises with distributed infrastructure. MACsec: Defense in Depth and Enterprise Security ExpressRoute Direct uniquely supports MACsec (IEEE 802.1AE) encryption at the data-link layer, allowing your router and Microsoft's router to establish encrypted communication even within the colocation facility. This optional feature provides additional security for compliance-sensitive workloads in banking or government environments. High-Performance Data Transfer for the Enterprise: Azure ExpressRoute Direct enables ultra-fast and secure data transfer between on-premises infrastructure and Azure by offering dedicated bandwidth of 10 to 100 Gbps. This high-speed connectivity is ideal for large-scale data movement scenarios such as AI workloads, backup, and disaster recovery. It ensures consistent performance, low latency, and enhanced reliability, making it well-suited for hybrid and multicloud environments that require frequent or time-sensitive data synchronization. FastPath Support: Azure ExpressRoute Direct now supports FastPath for Private Endpoints and Private Link, enabling low-latency, high-throughput connections by bypassing the virtual network gateway. This feature is available only with ExpressRoute Direct circuits (10 Gbps or 100 Gbps) and is in limited general availability. While a gateway is still needed for route exchange, traffic flows directly once FastPath is enabled. Supported gateway ExpressRoute Direct Setup Workflow Before provisioning ExpressRoute Direct resources, proper planning is essential. Key considerations for connectivity include understanding the two connectivity patterns available for ExpressRoute Direct from the customer edge to Microsoft Enterprise Edge (MSEE). Option 1: Colocation of Customer Equipment: This is a common pattern where the customer racks their network device (edge router) in the same third-party data center facility that houses Microsoft's networking gear (e.g., Equinix or NextDC). They install their router or firewall there and then order a short cross-connect from their cage to Microsoft's cage in that facility. The cross-connect is simply a fiber cable run through the facility's patch panel connecting the two parties. This direct colocation approach has the advantage of a single, highly efficient physical link (no intermediate hops) between the customer and Microsoft, completing the layer-1 connectivity in one step. Option 2: Using a Carrier/Exchange Provider: If the customer prefers not to move hardware into a new facility (due to cost or complexity), they can leverage a provider that already has presence in the relevant colocation. In this case, the customer connects from their data center to the provider's network, and the provider extends connectivity into the Microsoft peering location. For instance, the customer could contract with Megaport or a local telco to carry traffic from their on-premises location into Megaport's equipment, and Megaport in turn handles the cross-connection to Microsoft in the target facility. The conversation cited that the customer had already set up connections to Megaport in their data center. Using an exchange can simplify logistics since the provider arranges the cross-connect and often provides an LOA on the customer's behalf. It may also be more cost-effective where the customer's location is far from any Microsoft peering site. Many enterprises find that placing equipment in a well-connected colocation facility works best for their needs. Banks and large organizations have successfully taken this approach, such as placing routers in Equinix Sydney or NextDC Sydney to establish a direct fiber link to Azure. However, we understand that not every organization wants the capital expense or complexity of managing physical equipment in a new location. For those situations, using a cloud exchange like Megaport offers a practical alternative that still delivers the dedicated connectivity you're looking for, while letting someone else handle the infrastructure management. Once the decision on the connectivity pattern is made, the next step is to provision ExpressRoute Direct ports and establish the physical link: Step1: Provisioning Express Route Direct Ports Through the Azure portal (or CLI), the customer creates an ExpressRoute Direct resource. Customer must select an appropriate peering location, which corresponds to the colocation facility housing Azure's routers. For example, the customer would select the specific facility (such as "Vocus Auckland" or "Equinix Sydney SY2") where they intend to connect. Customer also choose the port bandwidth (either 10 Gbps or 100 Gbps) and the encapsulation type (Dot1Q or QinQ) during this setup. Azure then allocates two ports on two separate Microsoft devices in that location – essentially giving the customer a primary and secondary interface for redundancy, to remove a single point of failure affecting their connectivity. ****Critical considerations we need to keep in mind during this step**** Encapsulation: When configuring ExpressRoute Direct ports, the customer must choose an encapsulation method. Dot1Q (802.1Q) uses a single VLAN tag for the circuit, whereas Q-in-Q (802.1ad) uses stacked VLAN tags (an Outer S-Tag and Inner C-Tag). Q-in-Q allows multiple circuits on one physical port with overlapping customer VLAN IDs because Azure assigns a unique outer tag per circuit (making it ideal if the customer needs several ExpressRoute circuits on the same port). Dot1Q, by contrast, requires each VLAN ID to be unique across all circuits on the port, and is often used if the equipment doesn’t support Q-in-Q. (Most modern deployments prefer Q-in-Q for flexibility.) Capacity Planning: This offering allows customers to overprovision and utilize 20Gbps of capacity. Design for 10 Gbps with redundancy, not 20 Gbps total capacity. During Microsoft's monthly maintenance windows, one port may go offline, and your network must handle this seamlessly. Step 2: Generate Letter of Authorization After the ExpressRoute Direct resource is created, Microsoft generates a Letter of Authorization. The LOA is a document (often a PDF) that authorizes the data center operator to connect a specific Microsoft port to the designated port. It includes details like the facility name, patch panel identifier, and port numbers on Microsoft's side. If co-locating your own gear, you will also obtain a corresponding LOA from the facility for your port (or simply indicate your port details on the cross-connect order form). If a provider like Megaport is involved, that provider will generate an LOA for their port as well. Two LOAs are typically needed – one for Microsoft's ports and one for the other party's ports which are then submitted to the facility to execute the cross-connect. Step 3: Complete Cross Connect with data center provider Using the LOAs, the data center’s technicians will perform the cross-connection in the meet-me room. At this point, the physical fiber link is established between the Microsoft router and the customer (or provider) equipment. The link goes through a patch panel in the MMR – Meet me room rather than a direct cable between cages, for security and manageability. After patching, the circuit is in place but typically kept “administratively down” until ready. *****Critical considerations we need to keep in mind during this step. ***** When port allocation conflicts occur, engage Microsoft Support rather than recreating resources. They coordinate with colocation providers to resolve conflicts or issue new LOAs. Step 4: Change Admin Status of each link Once the cross-connect is physically completed, you can head into Azure's portal and flip the Admin State of each ExpressRoute Direct link to "Enabled." This action lights up the optical interface on Microsoft's side and starts your billing meter running, so you'll want to make sure everything is working properly first. The great thing is that Azure gives you visibility into the health of your fiber connection through optical power metrics. You can check the receive light levels right in the portal , a healthy connection should show power readings somewhere between -1 dBm and -9 dBm, which indicates a strong fiber signal. If you're seeing readings outside this range, or worse, no light at all, that's a red flag pointing to a potential issue like a mis-patch or faulty fiber connector. There was a real case where someone had a bad fiber connector that was caught because the light levels were too low, and the facility had to come back and re-patch the connection. So, this optical power check is really your first line of defence , once you see good light levels within the acceptable range, you know your physical layer is solid and you're ready to move on to the next steps. ****Critical considerations we need to keep in mind during this step. **** Proactive Monitoring: Set up alerts for BGP session failures and optical power thresholds. Link failures might not immediately impact users but require quick restoration to maintain full redundancy. At this stage, you've successfully navigated the physical infrastructure challenge, ExpressRoute Direct port pair is provisioned, fiber cross-connects are in place, and those critical optical power levels are showing healthy readings. Essentially, private physical highway directly connecting your network edge to Microsoft's backbone infrastructure has been built Step 5: Create Express Route Circuits ExpressRoute circuits represent the logical layer that transforms your physical ExpressRoute Direct ports into functional network connections. Through the Azure portal, organizations create circuit resources linked to their ExpressRoute Direct infrastructure, specifying bandwidth requirements and selecting the appropriate SKU (Local, Standard, or Premium) based on connectivity needs. A key advantage is the ability to provision multiple circuits on the same physical port pair, provided aggregate bandwidth stays within physical limits. For example, an organization with 10 Gbps ExpressRoute Direct might run a 1 Gbps non-production circuit alongside a 5 Gbps production circuit on the same infrastructure. Azure handles the technical complexity through automatic VLAN management: Step 6: Establish Peering Once your ExpressRoute circuit is created and VLAN connectivity is established, the next crucial step involves setting up BGP (Border Gateway Protocol) sessions between your network and Microsoft's infrastructure. ExpressRoute supports two primary BGP peering types: Private Peering for accessing Azure Virtual Networks and Microsoft Peering for reaching Microsoft SaaS services like Office 365 and Azure PaaS offerings. For most enterprise scenarios connecting data centers to Azure workloads, Private Peering becomes the focal point. Azure provides specific BGP IP addresses for your circuit configuration, defining /30 subnets for both primary and secondary link peering, which you'll configure on your edge router to exchange routing information. The typical flow involves your organization advertising on-premises network prefixes while Azure advertises VNet prefixes through these BGP sessions, creating dynamic route discovery between your environments. Importantly, both primary and secondary links maintain active BGP sessions, ensuring that if one connection fails, the secondary BGP session seamlessly maintains connectivity and keeps your network resilient against single points of failure. Step 7: Routing and Testing Once BGP sessions are established, your ExpressRoute circuit becomes fully operational, seamlessly extending your on-premises network into Azure virtual networks. Connectivity testing with ping, traceroute, and application traffic confirms that your on-premises servers can now communicate directly with Azure VMs through the private ExpressRoute path, bypassing the public internet entirely. The traffic remains completely isolated to your circuit via VLAN tags, ensuring no intermingling with other tenants while delivering the low latency and predictable performance that only dedicated connectivity can provide. At the end of this stage, the customer’s data center is linked to Azure at layer-3 via a private, resilient connection. They can access Azure resources as if they were on the same LAN extension, with low latency and high throughput. All that remains is to connect this circuit to relevant Azure virtual networks (via an ExpressRoute Gateway) and verify end-to-end application traffic. Step by step instructions are available as below Configure Azure ExpressRoute Direct using the Azure portal | Microsoft Learn Azure ExpressRoute: Configure ExpressRoute Direct | Microsoft Learn Azure ExpressRoute: Configure ExpressRoute Direct: CLI | Microsoft LearnProvide a Flat Network Scaling Solution to AKS - Azure CNI Pod Subnet - Static Block Allocation
We are excited to announce the general availability of Azure CNI Pod Subnet - Static Block Allocation – a networking solution that transforms how you scale Azure Kubernetes Service (AKS) clusters! This long-awaited feature is now here, providing enterprise-grade flat networking for clusters in unprecedented capacity. What is Azure CNI Pod Subnet - Static Block Allocation? Azure CNI Pod Subnet - Static Block Allocation revolutionizes AKS networking by expanding cluster capacity from 65K to 1M pods – a game-changing 15x increase that eliminates traditional scaling barriers. Instead of assigning a batch of random individual IP addresses to each node, this innovative approach assigns dedicated Azure subnet CIDR ranges directly to nodes. Every pod scheduled on a node receives its IP address from that node's pre-allocated CIDR block, raising IP limit and simplifying massive deployments. The result is you gain unmatched flexibility with separate node and pod subnets, granular control over NAT and NSG policies, isolated workloads at the pod level, and VNet-native pod networking that maintains peak performance. It also seamlessly works with Azure CNI Powered by Cilium to provide advanced networking capabilities and comprehensive network policy enforcement. Why is Azure CNI Pod Subnet - Static Block Allocation needed? Kubernetes network solutions are challenging to plan due to rapidly evolving business needs. AKS users often face difficulties balancing simplicity, security, and scalability, while environmental changes further increase management costs. Many AKS users need a flat network architecture, pods with direct inbound connectivity, and Azure-native solution integrations, but traditional flat networks couldn't scale beyond 65K pods. Until the launch of static block, customers either choose overlay networks to achieve massive scale or sacrifice the benefits of flat networking. Azure CNI Pod Subnet - Static Block Allocation enables VNet-routed IP addresses that can scale to over 1M pods, providing the simplicity and low latency of a flat network. Each node receives pre-allocated CIDR blocks, and all pods on that node obtain IP addresses from these ranges. This approach delivers massive scale, previously only available with overlay networks (up to 1M pods) while maintaining all the benefits of a flat network architecture. It also works seamlessly alongside Azure CNI Pod Subnet - Dynamic IP Allocation, simply deploy it on new node pools with dedicated subnets. AKS users can scale up AKS network solutions with minimal effort while maintaining enterprise-grade reliability and security. Key Benefits That Matter to You Massive Scale Increase: Break through the 65K pod limitation and scale up to 1M pods per cluster. This isn't just a number—it's about giving you the freedom to build and scale without hitting unexpected networking limits. High Performance: AKS users’ pods get routed on the VNet which is a benefit for ingress/egress, eliminating unnecessary network hops and reducing latency for VNet-native pod networking. Efficient IP Management: AKS users now can allocate CIDR blocks to nodes. This approach raises the IP scalability limit for large-scale deployments. Unmatched Flexibility: Work seamlessly with existing clusters with Azure CNI Pod Subnet - Dynamic IP Allocation Share pod subnets across multiple node pools or even different clusters. Scale your node and pod networks independently Granular Control and Security: Since pods get their own dedicated subnet, AKS users can: Apply different network security policies to pods vs. nodes. Configure customized NAT and NSG policies. Implement isolated workloads at the pod level. Learn more about Azure CNI Pod Subnet - Static Block Allocation Read more in Azure CNI Pod Subnet - Static Block Allocation and try it out in your environment today. Learn more about the solution limitations. Learn more about Azure Kubernetes Service.Inter-Hub Connectivity Using Azure Route Server
By Mays_Algebary shruthi_nair As your Azure footprint grows with a hub-and-spoke topology, managing User-Defined Routes (UDRs) for inter-hub connectivity can quickly become complex and error-prone. In this article, we’ll explore how Azure Route Server (ARS) can help streamline inter-hub routing by dynamically learning and advertising routes between hubs, reducing manual overhead and improving scalability. Baseline Architecture The baseline architecture includes two Hub VNets, each peered with their respective local spoke VNets as well as with the other Hub VNet for inter-hub connectivity. Both hubs are connected to local and remote ExpressRoute circuits in a bowtie configuration to ensure high availability and redundancy, with Weight used to prefer the local ExpressRoute circuit over the remote one. To maintain predictable routing behavior, the VNet-to-VNet configuration on the ExpressRoute Gateway should be disabled. Note: Adding ARS to an existing Hub with Virtual Network Gateway will cause downtime that expect to last 10 minutes. Scenario 1: ARS and NVA Coexist in the Hub Option A: Full Traffic Inspection ARS and NVA Coexist in the Hub In this scenario, ARS is deployed in each Hub VNet, alongside the Network Virtual Appliances (NVAs). NVA1 in Region1 establishes BGP peering with both the local ARS (ARS1) and the remote ARS (ARS2). Similarly, NVA2 in Region2 peers with both ARS2 (local) and ARS1 (remote). Let’s break down what each BGP peering relationship accomplishes. For clarity, we’ll focus on Region1, though the same logic applies to Region2: NVA1 Peering with Local ARS1 Through BGP peering with ARS1, NVA1 dynamically learns the prefixes of Spoke1 and Spoke2 at the OS level, eliminating the need to manually configure these routes. The same applies for NVA2 learning Spoke3 and Spoke4 prefixes via its BGP peering with ARS2. NVA1 Peering with Remote ARS2 When NVA1 peers with ARS2, the Spoke1 and Spoke2 prefixes are propagated to ARS2. ARS2 then injects these prefixes into NVA2 at both the NIC level with NVA1 as the next hop, and at the OS level. This mechanism removes the need for UDRs on the NVA subnets to enable inter-hub routing. Additionally, ARS2 advertises the Spoke1 and Spoke2 prefixes to both ExpressRoute circuits (EXR2 and EXR1 due to bowtie configuration) via GW2, making them reachable from on-premises through either EXR1 or EXR2. 👉Important: To ensure that ARS2 accepts and propagates Spoke1/Spoke2 prefixes received via NVA1, AS-Override must be enabled. Without AS-Override, BGP loop prevention will block these routes at ARS2, since both ARS1 and ARS2 use the default ASN 65515, and ARS2 will consider the route as already originated locally. The same principle applies in reverse for Spoke3 and Spoke4 prefixes being advertised from NVA2 to ARS1. Traffic Flow Inter-Hub Traffic: Spoke VNets are configured with UDRs that contain only a default route (0.0.0.0/0) pointing to the local NVA as the next hop. Additionally, the “Propagate Gateway Routes” setting should be set to False to ensure all traffic, whether East-West (intra-hub/inter-hub) or North-South (to/from internet), is forced through the local NVA for inspection. Local NVAs will have the next hop to the other region spokes injected at the NIC level by local ARS, pointing to the other region NVA, for example NVA2 will have next hop to Spoke1 and Spoke2 as NVA1 (10.0.1.4) and vice versa. Why are UDRs still needed on spokes if ARS handles dynamic routing? Even with ARS in place, UDRs are required to maintain control of the next hop for traffic inspection. For instance, if Spoke1 and Spoke2 do not have UDRs, they will learn the remote spoke prefixes (e.g., Spoke3/Spoke4) injected via ARS1, which received them from NVA2. This results in Spoke1/Spoke2 attempting to route traffic directly to NVA2, a path that is invalid, since the spokes don’t have the path to NVA2. The UDR ensures traffic correctly routes through NVA1 instead. On-Premises Traffic: To explain the on-premises traffic flow, we'll break it down into two directions: Azure to on-premises, and on-premises to Azure. Azure to On-Premises Traffic Flow: As previously noted, Spokes send all traffic, including traffic to on-premises, via NVA1 due to the default route in the UDR. NVA1 then routes traffic to the local ExpressRoute circuit, using Weight to prefer the local path over the remote. Note: While NVA1 learns on-premises prefixes from both local and remote ARSs at the OS level, this doesn’t affect routing decisions. The actual NIC-level route injection determines the next hop, ensuring traffic is sent via the correct path—even if the OS selects a different “best” route internally. The screenshot below from NVA1 shows four next hops to the on-premises network 10.2.0.0/16. These include the local ARS (ARS1: 10.0.2.5 and 10.0.2.4) and the remote ARS (ARS2: 10.1.2.5 and 10.1.2.4). On-Premises to Azure Traffic Flow In a bowtie ExpressRoute configuration, Azure VNet prefixes are advertised to on-premises through both local and remote ExpressRoute circuits. Because of this dual advertisement, the on-premises network must ensure optimal path selection when routing traffic to Azure. From Azure side, to maintain traffic symmetry, add UDRs at the GatewaySubnet (GW1 and GW2) with specific routes to the local Spoke VNets, using the local NVA as the next hop. This ensures return traffic flows back through the same path it entered. 👉How Does the ExpressRoute Edge Router Select the Optimal Path? You might ask: If Spoke prefixes are advertised by both GW1 and GW2, how does the ExpressRoute edge router choose the best path? (e.g., diagram below shows EXR1 learns Region1 prefixes from GW1 and GW2) Here’s how: Edge routers (like EXR1) receive the same Spoke prefixes from both gateways. However, these routes have different AS-Path lengths: - Routes from the local gateway (GW1) have a shorter AS-Path. - Routes from the remote gateway (GW2) have a longer AS-Path because NVA1’s ASN (e.g., 65001) is prepended twice as part of the AS-Override mechanism. As a result, the edge router (EXR1) will prefer the local path from GW1, ensuring efficient and predictable routing. For example: EXR1 receives Spoke1, Spoke2, and Hub1-VNet prefixes from both GW1 and GW2. But because the path via GW1 has a shorter AS-Path, EXR1 will select that as the best route. (Refer to the diagram below for a visual of the AS-Path difference). Final Traffic Flow: Option-A Insights: This design simplifies UDR configuration for inter-hub routing, especially useful when dealing with non-contiguous prefixes or operating across multiple hubs. For simplicity, we used a single NVA in each Hub-VNet while explaining the setup and traffic flow throughout this article. However, a high available (HA) NVA deployment is recommended. To maintain traffic symmetry in an HA setup, you’ll need to enable the next-hop IP feature when peering with Azure Route Server (ARS). When on-premises traffic inspection is required, the UDR setup in the GatewaySubnet becomes more complex as the number of Spokes increases. Additionally, each route table is currently limited to 400 UDR entries. As your Azure network scales, keep in mind that Azure Route Server supports a maximum of 8 BGP peers per instance (as of the time writing this article). This limit can impact architectures involving multiple NVAs or hubs. Option B: Bypass On-Premises Inspection If on-premises traffic inspection is not required, NVAs can advertise a supernet prefix summarizing the local Spoke VNets to the remote ARS. This approach provides granular control over which traffic is routed through the NVA and eliminates the need for BGP peering between the local NVA and local ARS. All other aspects of the architecture remain the same as described in Option A. For example, NVA2 can advertise the supernet 192.168.2.0/23 (supernet of Spoke3 and Spoke4) to ARS1. As a result, Spoke1 and Spoke2 will learn this route with NVA2 as the next hop. To ensure proper routing (as discussed earlier) and inter-hub inspection, you need apply a UDR in Spoke1 and Spoke2 that overrides this exact supernet prefix, redirecting traffic to NVA1 as the next hop. At the same time, traffic destined for on-premises will follow the system route through the local ExpressRoute gateway, bypassing NVA1 altogether. In this setup: UDRs on the Spokes should have "Propagate Gateway Routes" set to True. No UDRs are needed in the GatewaySubnet. 👉Can NVA2 Still Advertise Specific Spoke Prefixes? You might wonder: Can NVA2 still advertise specific prefixes (e.g., Spoke3 and Spoke4) learned from ARS2 to ARS1 instead of a supernet? Yes, this is technically possible, but it requires maintaining BGP peering between NVA2 and ARS2. However, this introduces UDR complexity in Spoke1 and Spoke2, as you'd need to manually override each specific prefix. This also defeats the purpose of using ARS for simplified route propagation, undermining the efficiency and scalability of the design. Bypass On-Premises Inspection Final Traffic Flow: Option B: Bypass on-premises inspection traffic flow Option-B Insights: This approach reduces the number of BGP peerings per ARS. Instead of maintaining two BGP sessions (local NVA and remote NVA) per Hub, you can limit it to just one, preserving capacity within ARS’s 8-peer limit for additional inter-hub NVA peerings. Each NVA should advertise a supernet prefix to the remote ARS. This can be challenging if your Spokes don’t use contiguous IP address spaces, as described in Option B. Scenario 2: ARS in the Hub and the NVA in Transit VNet In Scenario 1, we highlighted that when on-premises inspection is required, managing UDRs at the GatewaySubnet becomes increasingly complex as the number of Spoke VNets grows. This is due to the need for UDRs to include specific prefixes for each Spoke VNet. In this scenario, we eliminate the need to apply UDRs at the GatewaySubnet altogether. In this design, the NVA will be deployed in Transit VNet, where: Transit-VNet will be peered with local Spoke VNets and with the local Hub-VNet to enable intra-Hub and on-premises connectivity. Transit-VNet also peered with remote Transit VNets (e.g., Transit-VNet1 peered with Transit-VNet2) to handle inter-Hub connectivity through the NVAs. Additionally, Transit-VNets are peered with remote Hub-VNets, to establish BGP peering with the remote ARS. NVAs OS will need to add static routes for the local Spoke VNets prefixes, it can be specific or it can supernet prefix, which will later be advertised to ARSs over BGP Peering, then ARS will advertise it to on-premises via ExpressRoute. NVAs will BGP peer with local ARS and also with the remote ARS. To understand the reasoning behind this design, let’s take a closer look at the setup in Region1, focusing on how ARS and NVA are configured to connect to Region2. This will help illustrate both inter-hub and on-premises connectivity. The same concept applies in reverse from Region2 to Region1. Inetr-Hub: To enable NVA1 in Region1 to learn prefixes from Region2, NVA2 will configure static routes at the OS level for Spoke3 and Spoke4 (or their supernet prefix) and advertise them to ARS1 via remote BGP peering. As a result, these prefixes will be received by NVA1, both at the NIC level, with NVA2 as the next hop, and at the OS level for proper routing. Spoke1 and Spoke2 will have a UDR with a default route pointing to NVA1 as the next hop. For instance, when Spoke1 needs to communicate with Spoke3, the traffic will first route through NVA1. NVA1 will then forward the traffic to NVA2 using VNet peering between the two Hubs. A similar configuration will be applied in Region2, where NVA1 will configure static routes at the OS level for Spoke1 and Spoke2 (or their supernet prefix) and advertise them to ARS2 via remote BGP peering, as a result, these prefixes will be received by NVA2, both at the NIC level (injected by ARS2), with NVA1 as the next hop, and at the OS level for proper routing. Note: At the OS level, NVA1 learns Spoke3 and Spoke4 prefixes from both local and remote ARSs. However, the NIC-level route injection determines the actual next hop, so even if the OS selects a different best route, it won’t affect forwarding behavior. same applies to NVA2. On-Premises Traffic: To explain the on-premises traffic flow, we'll break it down into two directions: Azure to on-premises, and on-premises to Azure. Azure to On-Premises Traffic Flow: Spokes in Region1 route all traffic through NVA1 via a default route defined in their UDRs. Because of BGP peering between NVA1 and ARS1, ARS1 advertises the Spoke1 and Spoke2 (or their supernet prefix) to on-premises through ExpressRoute (EXR1). The Transit-VNet1 (hosting NVA1) is peered with Hub1-VNet, with “Use Remote Gateway” enabled. This allows NVA1 to learn on-premises prefixes from the local ExpressRoute gateway (GW1), and traffic to on-premises is routed through the local ExpressRoute circuit (EXR1) due to higher BGP Weight configuration. Note: At the OS level, NVA1 learns on-prem prefixes from both local and remote ARSs. However, the NIC-level route injection determines the actual next hop, so even if the OS selects a different best route, it won’t affect forwarding behavior. same applies to NVA2. On-Premises to Azure Traffic Flow: Through BGP peering with ARS1, NVA1 enables ARS1 to advertise Spoke1 and Spoke2 (or their supernet prefix) to both EXR1 and EXR2 circuits (due to the ExpressRoute bowtie setup). Additionally, due to BGP peering between NVA1 and ARS2, ARS2 also advertises Spoke1 and Spoke2 (or their supernet prefix) to EXR2 and EXR1 circuits. As a result, both ExpressRoute edge routers in Region1 and Region2 learn the same Spoke prefixes (or their supernet prefix) from both GW1 and GW2, with identical AS-Path lengths, as shown below. This causes non-optimal inbound routing, where traffic from on-premises destined to Region1 Spokes may first land in Region2’s Hub2-VNet before traversing to NVA1 in Region1. However, return traffic from Spoke1 and Spoke2 will always exit through Hub1-VNet. To prevent suboptimal routing, configure NVA1 to prepend the AS path for Spoke1 and Spoke2 (or their supernet prefix) when advertising them to the remote ARS2. Likewise, ensure NVA2 prepends the AS path for Spoke3 and Spoke4 (or their supernet prefix) when advertising to ARS1. This approach helps maintain optimal routing under normal conditions and during ExpressRoute failover scenarios. Below diagram shows NVA1 is setting AS-Prepend for Spoke1 and Spoke2 supernet prefix when BGP peer with remote ARS (ARS1), same will apply for NVA2 when advertising Spoke3 and Spoke4 prefixes to ARS1. Final Traffic Flow: Full Inspection: Traffic flow when NVA in Transit-VNet Insights: This solution is ideal when full traffic inspection is required. Unlike Scenario 1 - Option A, it eliminates the need for UDRs in the GatewaySubnet. When ARS is deployed in a VNet (typically in Hub VNets), the VNet will be limited to 500 VNet peerings (as of the time writing this article). However, in this design, Spokes peer with the Transit-VNet instead of directly with the ARS VNet, allowing you to scale beyond the 500-peer limit by leveraging Azure Virtual Network Manager (AVNM) or submitting a support request. Some enterprise customers may encounter the 1,000-route advertisement limit on the ExpressRoute circuit from the ExpressRoute gateway. In traditional hub-and-Spoke designs, there's no native control over what is advertised to ExpressRoute. With this architecture, NVAs provide greater control over route advertisement to the circuit. For simplicity, we used a single NVA in each Hub-VNet while explaining the setup and traffic flow throughout this article. However, a high available (HA) NVA deployment is recommended. To maintain traffic symmetry in an HA setup, you’ll need to enable the next-hop IP feature when peering with Azure Route Server (ARS). This design does require additional VNet peerings, including: Between Transit-VNets (inter-region), Between Transit-VNets and local Spokes, and Between Transit-VNets and both local and remote Hub-VNets.
