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In this lesson we cover Azure ExpressRoute FastPath, a data-plane optimization that increases throughput and lowers latency between your on-premises network and Azure Virtual Machines by bypassing bottlenecks at the virtual network gateway. FastPath accelerates packet forwarding for application traffic by creating a more direct data path between on-premises routers and Azure VMs. Control plane operations (gateway configuration, management, status) continue to use the virtual network gateway; only high-volume user/application data can take the FastPath route. Key benefits:
  • Higher packets-per-second and connections-per-second for application workloads.
  • Lower end-to-end latency for traffic between on-premises and Azure VMs.
  • Reduced data-plane load on the virtual network gateway.
How FastPath works:
  • The control plane still interacts with the virtual network gateway.
  • When enabled and supported by the gateway SKU, user/application data takes a bypass path (FastPath) that reduces the number of packet copies and context switches at the gateway.
  • FastPath is a property of the virtual network gateway connection and requires a compatible gateway SKU.
FastPath is a data-plane optimization — control-plane operations (gateway configuration, status, etc.) still flow through the virtual network gateway. Verify your gateway SKU supports FastPath before enabling it.
A screenshot of an Azure portal "ER-VNet-Connection | Configuration" page showing the Routing weight field and the FastPath checkbox checked, with the Save button highlighted. The left menu shows options like Overview, Activity log, Access control (IAM), Tags, and Configuration highlighted.
Prerequisites and compatibility
RequirementDetailsExample / Notes
Supported virtual network gateway SKUFastPath must be advertised by the gateway SKUFor example: UltraPerformance or ERGW3-AZ (confirm your subscription/region supports the SKU)
ExpressRoute connectionThe connection (VNet gateway connection under the ExpressRoute circuit) is the resource that has the FastPath optionThe connection links the virtual network gateway to the ExpressRoute circuit
Network configurationEnsure supported BGP and routing configurations are in placeAvoid conflicting policies that may steer traffic away from FastPath route
Before enabling FastPath, confirm the gateway SKU explicitly advertises FastPath support and that any virtual appliance, NVA, or firewall in the path supports the optimized data path. Enabling FastPath on an unsupported SKU will not produce the expected improvements.
How to enable FastPath
  • In the Azure portal:
    1. Open the ExpressRoute connection resource (this is the connection under your ExpressRoute circuit that links the virtual network gateway to the VNet).
    2. Go to the Configuration blade.
    3. Select the FastPath checkbox and Save.
  • Using Azure PowerShell:
    1. Retrieve the virtual network gateway connection resource.
    2. Set the ExpressRoute gateway bypass property to $true.
    3. Update the connection resource.
Example PowerShell to enable FastPath on a connection: 
$connection = Get-AzVirtualNetworkGatewayConnection -Name "labConnection" -ResourceGroupName "lab-rg"
$connection.ExpressRouteGatewayBypass = $true
Set-AzVirtualNetworkGatewayConnection -VirtualNetworkGatewayConnection $connection
Verify FastPath is enabled
  • PowerShell: check the connection property
$connection = Get-AzVirtualNetworkGatewayConnection -Name "labConnection" -ResourceGroupName "lab-rg"
$connection.ExpressRouteGatewayBypass  # should return True when FastPath is enabled
  • Azure portal: revisit the ExpressRoute connection Configuration blade to confirm the FastPath checkbox is checked.
Monitor and validate performance
  • Measure application throughput and latency before and after enabling FastPath to quantify improvements.
  • Monitor gateway metrics: packets-per-second, tunnel/connection status, and CPU/network counters where available.
  • Use Network Watcher tools (connection monitor, topology, packet capture) to validate traffic flows and latency.
Troubleshooting checklist
  • Confirm the gateway SKU supports FastPath and is available in your region/subscription.
  • Verify that no NVAs, firewalls, or intermediary devices are altering traffic in a way that prevents the FastPath data route.
  • Check for configuration issues in BGP or routing that might cause traffic to follow a different path.
  • If expected gains are not observed, roll back (disable FastPath) and re-run tests, then open a support case with Azure if necessary.
References and further reading After enabling FastPath, continue to validate application performance and monitor the gateway to ensure the change delivers the expected throughput and latency improvements.

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