Microsoft Unveils Outbound Network Segmentation for Azure App Service v3
Microsoft has introduced a new feature, Outbound Network Segmentation, for App Service Environment v3 on Azure. This feature, currently in public preview, enhances auditability and compliance for regulated workloads by offering precise control over outbound traffic routing from apps.
To utilise this feature, users must first create a new App Service Environment and enable the 'AlternateSubnetJoinEnabled' cluster setting during its creation. Once enabled, apps can be joined to alternate subnets at any time, provided the subnet is empty and delegated to Microsoft.web/serverfarms beforehand.
Outbound Network Segmentation allows for the definition of the subnet for outbound traffic, assignment of dedicated outbound IPs per app, routing of traffic through custom firewalls, and application of Network Security Groups with greater precision. Each plan in App Service Environment v3 can have up to 4 connections, and each app from a plan can only integrate with 1 alternate subnet. Microsoft, through the Azure App Service team, announced this feature on the official Microsoft Apps on Azure Blog on October 1, 2025.
Previously, all outbound traffic from an App Service Environment v3 originated from the full subnet range, making per-app restrictions challenging. This new feature enables fine-grained egress control at the app level, aligning with enterprise security policies and compliance requirements. However, application traffic routing must be enabled for the app to ensure all traffic is routed through the alternate subnet.
Outbound Network Segmentation, now in public preview and available in all Azure regions, offers enhanced control and precision in managing outbound traffic from apps in App Service Environment v3. By enabling this feature, users can better align with enterprise security policies and compliance requirements.
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