How VNet Peering Connects VNets Privately

What Azure VPN Gateway Is

Azure VPN Gateway is a specific type of virtual network gateway used to send encrypted network traffic between an Azure virtual network and an on-premises location, or between multiple virtual networks, across the public internet using IPsec/IKE VPN tunnels.

Why It Doesn't Meet the Requirement

While a VNet-to-VNet VPN gateway connection can connect virtual networks across regions, it fails to meet the scenario's constraints:

• Gateway requirement: It requires provisioning dedicated VPN gateway resources in each VNet.
• Bandwidth and latency constraints: VPN tunnels introduce encryption/decryption overhead and throughput limits (typically capped based on the gateway SKU).
• Unnecessary complexity: It is designed for encrypted site-to-site connectivity rather than the native, line-rate performance provided by VNet peering.

Key Characteristics and Limitations

• Throughput limits: Performance is bounded by gateway SKU throughput rather than VM network interface speeds.
• Encrypted tunnel overhead: Adds compute and packet encapsulation latency.
• Higher provisioning cost: Incurs continuous hourly costs for active gateway compute instances.

This Answer Would Be Correct If

The organization required encrypted site-to-site connectivity between an on-premises datacenter and Azure, or explicitly needed encrypted IPsec tunnels between VNets across non-peered environments.

Additional Context

For VNet-to-VNet communication within Azure, VNet peering is always preferred over VPN Gateways due to higher performance and lower operational cost.

What Azure DNS Private Zones Is

Azure DNS Private Zones is a managed Domain Name System (DNS) service that provides name resolution for virtual machines and services within and across virtual networks without needing custom DNS servers.

Why It Doesn't Meet the Requirement

• Name resolution only: Azure DNS Private Zones translates hostnames (like db.internal.contoso.com) into private IP addresses, but it does not provide the actual network routing or packet transport between VNets.
• No data path routing: Without an underlying network link such as VNet peering, virtual machines cannot route network packets across different VNets even if they can resolve each other's IP addresses.

Key Characteristics and Limitations

• Layer 7/Application service: Handles DNS queries and record management.
• Does not route traffic: Has no role in packet encapsulation, routing tables, or network interface forwarding.
• Complementary role: Used alongside VNet peering to allow VMs to find each other by name rather than hardcoded IPs.

This Answer Would Be Correct If

The organization already had network connectivity established between the VNets and specifically needed a service to resolve custom private domain names across those networks.

Additional Context

In production architectures, Azure DNS Private Zones are frequently linked to peered VNets to provide seamless name resolution across both networks.

What Azure ExpressRoute Is

Azure ExpressRoute is a dedicated, private connection service that extends on-premises networks directly into the Microsoft cloud over a private connection facilitated by a connectivity provider.

Why It Doesn't Meet the Requirement

• Wrong connectivity target: ExpressRoute connects on-premises datacenters or corporate offices to Azure cloud services; it is not the standard or direct mechanism for connecting two Azure VNets to each other.
• Requires physical circuits: ExpressRoute relies on dedicated physical telecom circuits and partner infrastructure.
• Cost and complexity: Implementing ExpressRoute for VNet-to-VNet traffic introduces extreme financial and architectural overhead.

Key Characteristics and Limitations

• Hybrid networking focus: Designed specifically for enterprise-to-cloud private connectivity.
• Provider dependent: Requires co-location facilities or network service providers.
• Complex provisioning: Involves ordering physical circuits, BGP peering, and ExpressRoute gateways.

This Answer Would Be Correct If

The requirement called for connecting an on-premises enterprise data center directly to Azure virtual networks over a dedicated private circuit without traversing the public internet.

Additional Context

While ExpressRoute circuits can connect multiple VNets via ExpressRoute FastPath/Gateway attachments in hybrid scenarios, VNet peering remains the native and optimal method for direct Azure-to-Azure VNet interconnection.