What are AWS Direct Connect and Azure ExpressRoute, and why would an enterprise use dedicated cloud connectivity instead of VPN over the internet?

Question

Accepted Answer

AWS Direct Connect and Azure ExpressRoute are dedicated network connections between an enterprise data center and the respective cloud provider. Instead of routing traffic over the public internet through an encrypted VPN tunnel, these services establish a private physical connection that provides more consistent performance, higher bandwidth, and often lower data transfer costs.

Direct Connect and ExpressRoute work by extending a private circuit from the enterprise network to a cloud provider point of presence, typically located in a colocation facility. The enterprise either deploys equipment in the same colocation facility or works with a network service provider to establish a connection from their data center to the colocation. At the meet-me point, the enterprise router peers with the cloud provider router using BGP to exchange routes between the on-premises network and the cloud VPCs or virtual networks.

The primary advantage is performance consistency. Internet-based VPN connections traverse the public internet where latency, jitter, and packet loss vary based on internet congestion, peering relationships, and the specific path traffic takes. These variations can degrade application performance unpredictably. Direct Connect and ExpressRoute bypass the public internet entirely, providing consistent latency and bandwidth because the traffic stays on private infrastructure managed by the enterprise and the cloud provider. For latency-sensitive applications like real-time databases, VoIP between on-premises and cloud, or financial trading systems, this consistency is essential.

Higher bandwidth is the second advantage. Internet VPN connections are limited by the enterprise internet circuit capacity and the overhead of VPN encryption. Direct Connect supports connection speeds from 1 Gbps to 100 Gbps, and ExpressRoute supports up to 100 Gbps. For workloads that transfer large amounts of data between on-premises and cloud, such as backup, replication, large-scale analytics, and migration, dedicated connections provide the bandwidth needed without competing with internet traffic.

Cost optimization is a significant factor for data-heavy workloads. Cloud providers charge for data transfer out of their network, and the per-gigabyte cost for traffic over the internet is typically higher than over dedicated connections. For organizations transferring terabytes of data monthly between on-premises and cloud, the reduced data transfer costs can offset the monthly cost of the dedicated connection.

Security is sometimes cited as an advantage, though it requires nuance. Direct Connect and ExpressRoute traffic does not traverse the public internet, which reduces exposure to internet-based attacks. However, the traffic is not encrypted by default on either service. If encryption is required for compliance or security policy, you must layer IPsec VPN on top of the dedicated connection or use provider-specific encryption features like MACsec on Direct Connect.

Most enterprises use a hybrid connectivity approach. Direct Connect or ExpressRoute provides the primary path for production traffic with its performance and cost advantages. A site-to-site VPN over the internet provides a backup path that activates if the dedicated connection fails. This combination provides the reliability of redundant paths with the performance of dedicated connectivity for normal operations.

Both services support virtual interfaces or peering configurations that allow access to multiple cloud services over a single physical connection. Direct Connect virtual interfaces can access VPCs in the same region, while a Direct Connect Gateway extends access to VPCs in other regions. ExpressRoute uses peering types for private connectivity to virtual networks and Microsoft peering for Microsoft 365 and Azure public services.