Enhancing Network Performance with MS Azure ExpressRoute FastPath

In today’s cloud-centric world, efficient and high-performance network connectivity is crucial for businesses. Microsoft Azure’s ExpressRoute FastPath is designed to significantly improve the data path performance between your on-premises network and your virtual network. This article delves into the features, configuration, and limitations of ExpressRoute FastPath.

What is ExpressRoute FastPath?
ExpressRoute FastPath is a feature that enhances the performance of data transfer between your on-premises network and your Azure virtual network. When enabled, FastPath sends network traffic directly to virtual machines (VMs) in the virtual network, bypassing the ExpressRoute virtual network gateway. This direct path reduces latency and improves throughput, making it ideal for performance-sensitive applications.

Availability and Support
FastPath is available on all ExpressRoute circuits. It supports virtual network peering and user-defined routes (UDR) over FastPath, which is now generally available in all regions within the public cloud. However, this support is only for connections associated with ExpressRoute Direct circuits. Additionally, limited general availability (GA) support for Private Endpoint/Private Link connectivity is available for connections associated with ExpressRoute Direct circuits, but only within limited regions and for specific services behind a private endpoint.

Configuration Requirements
To configure FastPath, you must have an ExpressRoute virtual network gateway. The gateway must be one of the following SKUs:

• Ultra Performance
• ErGw3AZ

For FastPath to function correctly, the hub virtual network and any peered spoke virtual networks must reside within the same region. It’s important to note that FastPath does not support globally peered virtual networks.

Limitations of FastPath
While FastPath offers significant performance improvements, it has some limitations:

• Load Balancers: If you deploy an Azure internal load balancer or an Azure PaaS service in your virtual network, network traffic from your on-premises network to the virtual IPs hosted on the load balancer is sent to the virtual network gateway.
• Gateway Transit: If you deploy two peered hub virtual networks connected to one circuit, you must set the Allow Gateway Transit on the virtual network peering to false. Otherwise, you will experience connectivity issues.
• Use Remote Gateway: If you deploy a spoke virtual network peered to two hub virtual networks, you can only use one hub gateway as the remote gateway. Using both as remote gateways will cause connectivity issues.
• Private Link: FastPath connectivity to a private endpoint or Private Link service over an ExpressRoute Direct circuit is supported for limited scenarios. It is not supported for ExpressRoute partner provider circuits.
• DNS Private Resolver: FastPath does not support connectivity to DNS Private Resolver.

IP Address Limits
FastPath has specific IP address limits based on the type of ExpressRoute circuit:

• ExpressRoute 100 Gbps Direct Port: 200,000 IP addresses
• ExpressRoute 10 Gbps Direct Port: 100,000 IP addresses
• ExpressRoute provider circuit (10 Gbps and lower): 25,000 IP addresses

Supported Regions and Services
FastPath support for Private Endpoint/Private Link connectivity is available for limited scenarios for 100/10Gbps ExpressRoute Direct connections. The supported Azure regions include:

• Australia East
• East Asia
• East US
• East US 2
• North Central US
• North Europe
• South Central US
• South East Asia
• UK South
• West Central US
• West Europe
• West US
• West US 2
• West US 3

FastPath Private Endpoint/Private Link connectivity is supported for the following Azure services:

• Azure Cosmos DB
• Azure Key Vault
• Azure Storage
• Third Party Private Link Services

Conclusion
ExpressRoute FastPath is a powerful feature that enhances the performance of data transfer between your on-premises network and your Azure virtual network. By understanding its configuration requirements and limitations, you can effectively leverage FastPath to optimize your network performance and support your business-critical applications.