A Guide to Azure Data Transfer Pricing
Understanding Azure networking charges is essential for businesses aiming to manage their budgets effectively. Given the complexity of Azure networking pricing, which involves various influencing factors, the goal here is to bring a clearer understanding of the associated data transfer costs by breaking down the pricing models into the following use cases: VM to VM VM to Private Endpoint VM to Internal Standard Load Balancer (ILB) VM to Internet Hybrid connectivity Please note this is a first version, with a second version to follow that will include additional scenarios. Disclaimer: Pricing may change over time, check the public Azure pricing calculator for up-to-date pricing information. Actual pricing may vary depending on agreements, purchase dates, and currency exchange rates. Sign in to the Azure pricing calculator to see pricing based on your current program/offer with Microsoft. 1. VM to VM 1.1. VM to VM, same VNet Data transfer within the same virtual network (VNet) is free of charge. This means that traffic between VMs within the same VNet will not incur any additional costs. Doc. Data transfer across Availability Zones (AZ) is free. Doc. 1.2. VM to VM, across VNet peering Azure VNet peering enables seamless connectivity between two virtual networks, allowing resources in different VNets to communicate with each other as if they were within the same network. When data is transferred between VNets, charges apply for both ingress and egress data. Doc: VM to VM, across VNet peering, same region VM to VM, across Global VNet peering Azure regions are grouped into 3 Zones (distinct from Avaialbility Zones within a specific Azure region). The pricing for Global VNet Peering is based on that geographic structure. Data transfer between VNets in different zones incurs outbound and inbound data transfer rates for the respective zones. When data is transferred from a VNet in Zone 1 to a VNet in Zone 2, outbound data transfer rates for Zone 1 and inbound data transfer rates for Zone 2 will be applicable. Doc. 1.3. VM to VM, through Network Virtual Appliance (NVA) Data transfer through an NVA involves charges for both ingress and egress data, depending on the volume of data processed. When an NVA is in the path, such as for spoke VNet to spoke VNet connectivity via an NVA (firewall...) in the hub VNet, it incurs VM to VM pricing twice. The table above reflects only data transfer charges and does not include NVA/Azure Firewall processing costs. 2. VM to Private Endpoint (PE) Private Endpoint pricing includes charges for the provisioned resource and data transfer costs based on traffic direction. For instance, writing to a Storage Account through a Private Endpoint incurs outbound data charges, while reading incurs inbound data charges. Doc: 2.1. VM to PE, same VNet Since data transfer within a VNet is free, charges are only applied for data processing through the Private Endpoint. Cross-region traffic will incur additional costs if the Storage Account and the Private Endpoint are located in different regions. 2.2. VM to PE, across VNet peering Accessing Private Endpoints from a peered network incurs only Private Link Premium charges, with no peering fees. Doc. VM to PE, across VNet peering, same region VM to PE, across VNet peering, PE region != SA region 2.3. VM to PE, through NVA When an NVA is in the path, such as for spoke VNet to spoke VNet connectivity via a firewall in the hub VNet, it incurs VM to VM charges between the VM and the NVA. However, as per the PE pricing model, there are no charges between the NVA and the PE. The table above reflects only data transfer charges and does not include NVA/Azure Firewall processing costs. 3. VM to Internal Load Balancer (ILB) Azure Standard Load Balancer pricing is based on the number of load balancing rules as well as the volume of data processed. Doc: 3.1. VM to ILB, same VNet Data transfer within the same virtual network (VNet) is free. However, the data processed by the ILB is charged based on its volume and on the number load balancing rules implemented. Only the inbound traffic is processed by the ILB (and charged), the return traffic goes direct from the backend to the source VM (free of charge). 3.2. VM to ILB, across VNet peering In addition to the Load Balancer costs, data transfer charges between VNets apply for both ingress and egress. 3.3. VM to ILB, through NVA When an NVA is in the path, such as for spoke VNet to spoke VNet connectivity via a firewall in the hub VNet, it incurs VM to VM charges between the VM and the NVA and VM to ILB charges between the NVA and the ILB/backend resource. The table above reflects only data transfer charges and does not include NVA/Azure Firewall processing costs. 4. VM to internet 4.1. Data transfer and inter-region pricing model Bandwidth refers to data moving in and out of Azure data centers, as well as data moving between Azure data centers; other transfers are explicitly covered by the Content Delivery Network, ExpressRoute pricing, or Peering. Doc: 4.2. Routing Preference in Azure and internet egress pricing model When creating a public IP in Azure, Azure Routing Preference allows you to choose how your traffic routes between Azure and the Internet. You can select either the Microsoft Global Network or the public internet for routing your traffic. Doc: See how this choice can impact the performance and reliability of network traffic: By selecting a Routing Preference set to Microsoft network, ingress traffic enters the Microsoft network closest to the user, and egress traffic exits the network closest to the user, minimizing travel on the public internet (“Cold Potato” routing). On the contrary, setting the Routing Preference to internet, ingress traffic enters the Microsoft network closest to the hosted service region. Transit ISP networks are used to route traffic, travel on the Microsoft Global Network is minimized (“Hot Potato” routing). Bandwidth pricing for internet egress, Doc: 4.3. VM to internet, direct Data transferred out of Azure to the internet incurs charges, while data transferred into Azure is free of charge. Doc. It is important to note that default outbound access for VMs in Azure will be retired on September 30 2025, migration to an explicit outbound internet connectivity method is recommended. Doc. 4.4. VM to internet, with a public IP Here a standard public IP is explicitly associated to a VM NIC, that incurs additional costs. Like in the previous scenario, data transferred out of Azure to the internet incurs charges, while data transferred into Azure is free of charge. Doc. 4.5. VM to internet, with NAT Gateway In addition to the previous costs, data transfer through a NAT Gateway involves charges for both the data processed and the NAT Gateway itself, Doc: 5. Hybrid connectivity Hybrid connectivity involves connecting on-premises networks to Azure VNets. The pricing model includes charges for data transfer between the on-premises network and Azure, as well as any additional costs for using Network Virtual Appliances (NVAs) or Azure Firewalls in the hub VNet. 5.1. H&S Hybrid connectivity without firewall inspection in the hub For an inbound flow, from the ExpressRoute Gateway to a spoke VNet, VNet peering charges are applied once on the spoke inbound. There are no charges on the hub outbound. For an outbound flow, from a spoke VNet to an ER branch, VNet peering charges are applied once, outbound of the spoke only. There are no charges on the hub inbound. Doc. The table above does not include ExpressRoute connectivity related costs. 5.2. H&S Hybrid connectivity with firewall inspection in the hub Since traffic transits and is inspected via a firewall in the hub VNet (Azure Firewall or 3P firewall NVA), the previous concepts do not apply. “Standard” inter-VNet VM-to-VM charges apply between the FW and the destination VM : inbound and outbound on both directions. Once outbound from the source VNet (Hub or Spoke), once inbound on the destination VNet (Spoke or Hub). The table above reflects only data transfer charges within Azure and does not include NVA/Azure Firewall processing costs nor the costs related to ExpressRoute connectivity. 5.3. H&S Hybrid connectivity via a 3rd party connectivity NVA (SDWAN or IPSec) Standard inter-VNet VM-to-VM charges apply between the NVA and the destination VM: inbound and outbound on both directions, both in the Hub VNet and in the Spoke VNet. 5.4. vWAN scenarios VNet peering is charged only from the point of view of the spoke – see examples and vWAN pricing components. Next steps with cost management To optimize cost management, Azure offers tools for monitoring and analyzing network charges. Azure Cost Management and Billing allows you to track and allocate costs across various services and resources, ensuring transparency and control over your expenses. By leveraging these tools, businesses can gain a deeper understanding of their network costs and make informed decisions to optimize their Azure spending.Inspection Patterns in Hub-and-Spoke and vWAN Architectures
By shruthi_nair Mays_Algebary Inspection plays a vital role in network architecture, and each customer may have unique inspection requirements. This article explores common inspection scenarios in both Hub-and-Spoke and Virtual WAN (vWAN) topologies. We’ll walk through design approaches assuming a setup with two Hubs or Virtual Hubs (VHubs) connected to on-premises environments via ExpressRoute. The specific regions of the Hubs or VHubs are not critical, as the same design principles can be applied across regions. Scenario1: Hub-and-Spoke Inspection Patterns In the Hub-and-Spoke scenarios, the baseline architecture assumes the presence of two Hub VNets. Each Hub VNet is peered with its local spoke VNets as well as with the other Hub VNet (Hub2-VNet). Additionally, both Hub VNets are connected to both local and remote ExpressRoute circuits to ensure redundancy. Note: In Hub-and-Spoke scenarios, connectivity between virtual networks over ExpressRoute circuits across Hubs is intentionally disabled. This ensures that inter-Hub traffic uses VNet peering, which provides a more optimized path, rather than traversing the ExpressRoute circuit. In Scenario 1, we present two implementation approaches: a traditional method and an alternative leveraging Azure Virtual Network Manager (AVNM). Option1: Full Inspection A widely adopted design pattern is to inspect all traffic, both east-west and north-south, to meet security and compliance requirements. This can be implemented using a traditional Hub-and-Spoke topology with VNet Peering and User-Defined Routes (UDRs), or by leveraging AVNM with Connectivity Configurations and centralized UDR management. In the traditional approach: VNet Peering is used to connect each spoke to its local Hub, and to establish connectivity between the two Hubs. UDRs direct traffic to the firewall as the next hop, ensuring inspection before reaching its destination. These UDRs are applied at the Spoke VNets, the Gateway Subnet, and the Firewall Subnet (especially for inter-region scenarios), as shown in the below diagram. As your environment grows, managing individual UDRs and VNet Peerings manually can become complex. To simplify deployment and ongoing management at scale, you can use AVNM. With AVNM: Use the Hub-and-Spoke connectivity configuration to manage routing within a single Hub. Use the Mesh connectivity configuration to establish Inter-Hub connectivity between the two Hubs. AVNM also enables centralized creation, assignment, and management of UDRs, streamlining network configuration at scale. Connectivity Inspection Table Connectivity Scenario Inspected On-premises ↔ Azure ✅ Spoke ↔ Spoke ✅ Spoke ↔ Internet ✅ Option2: Selective Inspection Between Azure VNets In some scenarios, full traffic inspection is not required or desirable. This may be due to network segmentation based on trust zones, for example, traffic between trusted VNets may not require inspection. Other reasons include high-volume data replication, latency-sensitive applications, or the need to reduce inspection overhead and cost. In this design, VNets are grouped into trusted and untrusted zones. Trusted VNets can exist within the same Hub or across different Hubs. To bypass inspection between trusted VNets, you can connect them directly using VNet Peering or AVNM Mesh connectivity topology. It’s important to note that UDRs are still used and configured as described in the full inspection model (Option 1). However, when trusted VNets are directly connected, system routes (created by VNet Peering or Mesh connectivity) take precedence over custom UDRs. As a result, traffic between trusted VNets bypasses the firewall and flows directly. In contrast, traffic to or from untrusted zones follows the UDRs, ensuring it is routed through the firewall for inspection. t Connectivity Inspection Table Connectivity Scenario Inspected On-premises ↔ Azure ✅ Spoke ↔ Internet ✅ Spoke ↔ Spoke (Same Zones) ❌ Spoke ↔ Spoke (Across Zones) ✅ Option3: No Inspection to On-premises In cases where a firewall at the on-premises or colocation site already inspects traffic from Azure, customers typically aim to avoid double inspection. To support this in the above design, traffic destined for on-premises is not routed through the firewall deployed in Azure. For the UDRs applied to the spoke VNets, ensure that "Propagate Gateway Routes" is set to true, allowing traffic to follow the ExpressRoute path directly without additional inspection in Azure. Connectivity Inspection Table Connectivity Scenario Inspected On-premises ↔ Azure ❌ Spoke ↔ Spoke ✅ Spoke ↔ Internet ✅ Option4: Internet Inspection Only While not generally recommended, some customers choose to inspect only internet-bound traffic and allow private traffic to flow without inspection. In such cases, spoke VNets can be directly connected using VNet Peering or AVNM Mesh connectivity. To ensure on-premises traffic avoids inspection, set "Propagate Gateway Routes" to true in the UDRs applied to spoke VNets. This allows traffic to follow the ExpressRoute path directly without being inspected in Azure. Scenario2: vWAN Inspection Options Now we will explore inspection options using a vWAN topology. Across all scenarios, the base architecture assumes two Virtual Hubs (VHubs), each connected to its respective local spoke VNets. vWAN provides default connectivity between the two VHubs, and each VHub is also connected to both local and remote ExpressRoute circuits for redundancy. It's important to note that this discussion focuses on inspection in vWAN using Routing Intent. As a result, bypassing inspection for traffic to on-premises is not supported in this model. Option1: Full Inspection As noted earlier, inspecting all traffic, both east-west and north-south, is a common practice to fulfill compliance and security needs. In this design, enabling Routing Intent provides the capability to inspect both, private and internet-bound traffic. Unlike the Hub-and-Spoke topology, this approach does not require any UDR configuration. Connectivity Inspection Table Connectivity Scenario Inspected On-premises ↔ Azure ✅ Spoke ↔ Spoke ✅ Spoke ↔ Internet ✅ Option2: Using Different Firewall Flavors for Traffic Inspection Using different firewall flavors inside VHub for traffic inspection Some customers require specific firewalls for different traffic flows, for example, using Azure Firewall for East-West traffic while relying on a third-party firewall for North-South inspection. In vWAN, it’s possible to deploy both Azure Firewall and a third-party network virtual appliance (NVA) within the same VHub. However, as of this writing, deploying two different third-party NVAs in the same VHub is not supported. This behavior may change in the future, so it’s recommended to monitor the known limitations section for updates. With this design, you can easily control which firewall handles East-West versus North-South traffic using Routing Intent, eliminating the need for UDRs. Using different firewall flavors inside VHub for traffic inspection Deploying third-party firewalls in spoke VNets when VHub limitations apply If the third-party firewall you want to use is not supported within the VHub, or if the managed firewall available in the VHub lacks certain required features compared to the version deployable in a regular VNet, you can deploy the third-party firewall in a spoke VNet instead, while using Azure Firewall in the VHub. In this design, the third-party firewall (deployed in a spoke VNet) handles internet-bound traffic, and Azure Firewall (in the VHub) inspects East-West traffic. This setup is achieved by peering the third-party firewall VNet to the VHub, as well as directly peering it with the spoke VNets. These spoke VNets are also connected to the VHub, as illustrated in the diagram below. UDRs are required in the spoke VNets to forward internet-bound traffic to the third-party firewall VNet. East-West traffic routing, however, is handled using the Routing Intent feature, directing traffic through Azure Firewall without the need for UDRs. Deploying third-party firewalls in spoke VNets when VHub limitations apply Note: Although it is not required to connect the third-party firewall VNet to the VHub for traffic flow, doing so is recommended for ease of management and on-premises reachability. Connectivity Inspection Table Connectivity Scenario Inspected On-premises ↔ Azure ✅ Inspected using Azure Firewall Spoke ↔ Spoke ✅ Inspected using Azure Firewall Spoke ↔ Internet ✅ Inspected using Third Party Firewall Option3: Selective Inspection Between Azure VNets Similar to the Hub-and-Spoke topology, there are scenarios where full traffic inspection is not ideal. This may be due to Azure VNets being segmented into trusted and untrusted zones, where inspection is unnecessary between trusted VNets. Other reasons include large data replication between specific VNets or latency-sensitive applications that require minimizing inspection delays and associated costs. In this design, trusted and untrusted VNets can reside within the same VHub or across different VHubs. Routing Intent remains enabled to inspect traffic between trusted and untrusted VNets, as well as internet-bound traffic. To bypass inspection between trusted VNets, you can connect them directly using VNet Peering or AVNM Mesh connectivity. Unlike the Hub-and-Spoke model, this design does not require UDR configuration. Because trusted VNets are directly connected, system routes from VNet peering take precedence over routes learned through the VHub. Traffic destined for untrusted zones will continue to follow the Routing Intent and be inspected accordingly. Connectivity Inspection Table Connectivity Scenario Inspected On-premises ↔ Azure ✅ Spoke ↔ Internet ✅ Spoke ↔ Spoke (Same Zones) ❌ Spoke ↔ Spoke (Across Zones) ✅ Option4: Internet Inspection Only While not generally recommended, some customers choose to inspect only internet-bound traffic and bypass inspection of private traffic. In this design, you only enable the Internet Inspection option within Routing Intent, so private traffic bypasses the firewall entirely. The VHub manages both intra-and inter-VHub routing directly. Internet Inspection Only Connectivity Inspection Table Connectivity Scenario Inspected On-premises ↔ Azure ❌ Spoke ↔ Internet ✅ Spoke ↔ Spoke ❌Understanding ExpressRoute private peering to address ExpressRoute resiliency
This article provides an overview of Microsoft ExpressRoute, including its various components such as the Circuit, the Gateway and the Connection, and different connectivity models like ExpressRoute Service Provider and ExpressRoute Direct. It also covers the resilience and failure scenarios related to ExpressRoute, including geo-redundancy, Availability Zones, and route advertisement limits. If you're looking to learn more about ExpressRoute and its implementation, this article is a great resource.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.Network Redundancy from On-Premises to Azure VMware and VNETs in a Single-Region Design
By shruthi_nair Mays_Algebary 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 guide presents common architectural patterns for building redundant connectivity between on-premises datacenters, Azure Virtual Networks (VNets), and Azure VMware Solution (AVS) within a single-region deployment. AVS allows organizations to run VMware-based workloads directly on Azure infrastructure, offering a streamlined path for migrating existing VMware environments to the cloud without the need for significant re-architecture or modification. Connectivity Between AVS, On-Premises, and Virtual Networks The diagram below illustrates a common network design pattern using either a Hub-and-Spoke or Virtual WAN (vWAN) topology, deployed within a single Azure region. ExpressRoute is used to establish connectivity between on-premises environments and VNets. The same ExpressRoute circuit is extended to connect AVS to the on-premises infrastructure through ExpressRoute Global Reach. Consideration: This design presents a single point of failure. If the ExpressRoute circuit (ER1-EastUS) experiences an outage, connectivity between the on-premises environment, VNets, and AVS will be disrupted. Let’s examine some solutions to establish redundant connectivity in case the ER1-EastUS experiences an outage. Solution1: Network Redundancy via VPN In this solution, one or more VPN tunnels are deployed as a backup to ExpressRoute. If ExpressRoute becomes unavailable, the VPN provides an alternative connectivity path from the on-premises environment to VNets and AVS. 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. 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. Latency: The VPN tunnel introduces additional latency due to its reliance on the public internet and the overhead associated with encryption. Bandwidth Considerations: Multiple VPN tunnels might be needed to achieve bandwidth comparable to a high-capacity ExpressRoute circuit (e.g., over 10G). For details on VPN gateway SKU and tunnel throughput, refer to this link. Solution2: Network Redundancy via SD-WAN In this solution, SDWAN tunnels are deployed as a backup to ExpressRoute. If ExpressRoute becomes unavailable, SDWAN provides an alternative connectivity path from the on-premises environment to VNets and AVS. In a Hub-and-Spoke topology, a backup path to and from AVS can be established by deploying ARS in the hub VNet. ARS enables seamless transit routing between ExpressRoute and the SDWAN appliance. In vWAN topology, ARS is not required. The vHub's built-in routing service automatically provides transitive routing between the SDWAN and ExpressRoute. Note: In vWAN topology, to ensure optimal convergence from the VNets when failing back to ExpressRoute, prepend the prefixes advertised from on-premises over the SDWAN to make sure it's longer that ExpressRoute learned routes. If you don't prepend, VNets will continue to use SDWAN path to on-prem as primary path. In this design using Azure vWAN, the SD-WAN can be deployed either within the vHub or in a spoke VNet connected to the vHub the same principle applies in both cases. Solution Insights: If you have an existing SDWANs no additional deployment is needed. Bandwidth Considerations: Vendor specific. Management consideration: Third party dependency and need to manage the HA deployment, except for SD-WAN SaaS solution. Solution3: Network Redundancy via ExpressRoute in Different Peering Locations Deploy an additional ExpressRoute circuit at a different peering location and enable Global Reach between ER2-peeringlocation2 and AVS-ER. To use this circuit as a backup path, prepend the on-premises prefixes on the second circuit; otherwise, AVS or VNet will perform Equal-Cost Multi-Path (ECMP) routing across both circuits to on-prem. Note: Use public ASN to prepend the on-premises prefix as AVS-ER will strip the private ASN toward AVS. Refer to this link for more details. Solution Insights: Ideal for mission-critical applications, providing predictable throughput and bandwidth for backup. Could be cost prohibitive depending on the bandwidth of the second circuit. Solution4: Network Redundancy via Metro ExpressRoute Metro ExpressRoute is the new ExpressRoute configuration. This configuration allows you to benefit from a dual-homed setup that facilitates diverse connections to two distinct ExpressRoute peering locations within a city. This configuration offers enhanced resiliency if one peering location experiences an outage. Solution Insights Higher Resiliency: Provides increased reliability with a single circuit. Limited regional availability: Availability is restricted to specific regions within the metro area. Cost-effective Conclusion: The choice of failover connectivity should be guided by the specific latency and bandwidth requirements of your workloads. Ultimately, achieving high availability and ensuring continuous operations depend on careful planning and effective implementation of network redundancy strategies.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 600 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. EXR1 learns Region1 Spokes's supernet prefixes from GW1 and GW2 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.
