Azure ExpressRoute and VPN Gateway offer distinct ways to connect your on-premises network to Azure, each with unique trade-offs in performance, cost, and complexity.
Let’s see ExpressRoute in action, provisioning a basic circuit.
az network express-route create \
--name MyExpressRouteCircuit \
--resource-group MyResourceGroup \
--location eastus \
--sku Standard_UltraLowLatency \
--allow-global-reach True \
--bandwidth 100 \
--tags Environment=Production
This command establishes a dedicated, private connection. The sku dictates performance and pricing, while allow-global-reach enables access to Azure services across all regions, not just the one where the circuit is provisioned. The bandwidth is provisioned in Mbps.
Now, let’s provision a comparable VPN Gateway.
az network vnet-gateway create \
--name MyVpnGateway \
--resource-group MyResourceGroup \
--location eastus \
--sku VpnGw2 \
--gateway-type Vpn \
--vpn-type RouteBased \
--vnet-name MyVnet \
--public-ip-address MyVpnGatewayIp \
--enable-Bgp True
This creates a Virtual Private Network gateway. The sku here (e.g., VpnGw2) determines throughput and concurrent connection limits. vpn-type RouteBased is generally preferred for Azure VPN Gateways as it offers more flexibility. enable-Bgp allows for dynamic routing.
The core difference lies in the underlying network path. ExpressRoute leverages dedicated, private fiber optic connections through a Microsoft-approved network provider. This bypasses the public internet entirely, offering consistent, high-bandwidth, low-latency connectivity. Think of it as having a private leased line into Azure’s datacenter.
VPN Gateway, on the other hand, establishes a secure, encrypted tunnel over the public internet. While it uses IPsec/IKE protocols to ensure data confidentiality and integrity, its performance is subject to the inherent variability and potential congestion of the internet. It’s akin to a secure, encrypted tunnel through a public highway.
Here’s a practical scenario. A financial institution requires guaranteed bandwidth and sub-50ms latency for real-time trading applications connecting to their Azure-hosted trading platforms. They would choose ExpressRoute for its predictable performance and dedicated capacity. The cost is higher, but the SLA and reliability are paramount.
Conversely, a small business needing to connect their office to a few Azure virtual machines for file sharing and basic application access might opt for VPN Gateway. The cost is significantly lower, and the internet’s variability is acceptable for their use case. They would configure a Site-to-Site VPN connection, establishing an IPsec tunnel between their on-premises firewall/router and the Azure VPN Gateway.
The configuration for ExpressRoute involves coordinating with a connectivity provider (e.g., Equinix, AT&T, Verizon) to provision a physical circuit to an Azure ExpressRoute location. You then create an ExpressRoute circuit in Azure and associate a virtual network gateway with it.
For VPN Gateway, you create a Virtual Network Gateway within your Azure Virtual Network and then create a local network gateway representing your on-premises network. Finally, you establish a connection resource in Azure linking the Virtual Network Gateway to the Local Network Gateway, specifying shared keys for authentication.
A common misconception is that VPN Gateway is always "cheaper." While the upfront Azure gateway cost might appear lower, consider the total cost of ownership. VPN Gateway relies on your internet bandwidth, and if you need to upgrade your internet circuit to achieve higher throughput for your VPN, that cost is separate. ExpressRoute’s bandwidth is provisioned directly and often comes with a Service Level Agreement (SLA) for uptime and performance, which VPN Gateway does not provide.
ExpressRoute has different peering types: Azure Private, Azure Public, and Microsoft. Azure Private peering is used for accessing resources within your Azure Virtual Networks. Azure Public peering allows access to Microsoft’s public IP address ranges (like Office 365). Microsoft peering is for accessing Microsoft 365 services directly, bypassing the public internet for those specific services.
When troubleshooting connectivity issues with VPN Gateway, a common pitfall is mismatched IKE/IPsec parameters between the on-premises device and the Azure VPN Gateway. Ensure the Phase 1 (IKE) and Phase 2 (IPsec) encryption, hashing, Diffie-Hellman group, and SA lifetimes are identical on both ends. The az network vpn-connection show --gateway-name MyVpnGateway --name MyConnection --resource-group MyResourceGroup --output table command can show the current connection status and negotiated parameters.
For ExpressRoute, a frequent cause of performance degradation is exceeding the provisioned bandwidth. Monitoring the ExpressRoute circuit utilization in the Azure portal is crucial. Also, ensure your network provider is meeting their SLAs for the physical circuit.
The next step after establishing robust connectivity is often optimizing traffic flow and security policies between your on-premises and Azure environments.