Connect an on-premises network to Azure

ExpressRoute
Virtual Network
VPN Gateway

This article compares three options for connecting an on-premises network to an Azure Virtual Network (VNet). For each option, a more detailed reference architecture is available.

VPN connection

A VPN gateway is a type of virtual network gateway that sends encrypted traffic between an Azure virtual network and an on-premises location. The encrypted traffic goes over the public Internet.

This architecture is suitable for hybrid applications where the traffic between on-premises hardware and the cloud is likely to be light, or you're willing to trade slightly extended latency for the flexibility and processing power of the cloud.

Diagram of a VPN gateway.

Benefits

  • Simple to configure.
  • Much higher aggregate bandwidth available; up to 10 Gbps depending on the VPN Gateway SKU.

Challenges

  • Requires an on-premises VPN device.
  • Although Microsoft guarantees 99.9% availability for each VPN Gateway, this SLA only covers the VPN gateway, and not your network connection to the gateway.

Reference architecture

Azure ExpressRoute connection

ExpressRoute connections use a private, dedicated connection through a third-party connectivity provider. The private connection extends your on-premises network into Azure.

This architecture is suitable for hybrid applications running large-scale, mission-critical workloads that require a high degree of scalability.

Diagram of a VPN gateway.

Note

In the context of ExpressRoute, the Microsoft Edge describes the edge routers on the Microsoft side of the ExpressRoute circuit. This is the ExpressRoute circuit's point of entry into Microsoft's network.

Benefits

  • Much higher bandwidth available; up to 10 Gbps depending on the connectivity provider.
  • Lower and more consistent latencies compared to typical connections over the Internet.
  • Supports dynamic scaling of bandwidth to help reduce costs during periods of lower demand. However, not all connectivity providers have this option.
  • May allow your organization direct access to national clouds, depending on the connectivity provider.
  • 99.9% availability SLA across the entire connection.

Challenges

  • Can be complex to set up. Creating an ExpressRoute connection requires working with a third-party connectivity provider. The provider is responsible for provisioning the network connection.
  • Requires high-bandwidth routers on-premises.

Reference architecture

ExpressRoute with VPN failover

This option combines the previous two, using ExpressRoute in normal conditions, but failing over to a VPN connection if there's a loss of connectivity in the ExpressRoute circuit.

This architecture is suitable for hybrid applications that need the higher bandwidth of ExpressRoute, and also require highly available network connectivity.

Benefits

  • High availability if the ExpressRoute circuit fails, although the fallback connection is on a lower bandwidth network.

Challenges

  • Complex to configure. You need to set up both a VPN connection and an ExpressRoute circuit.
  • Requires redundant hardware (VPN appliances), and a redundant Azure VPN Gateway connection for which you pay charges.

Reference architecture

Reference architectures