Final answer:
Azure Virtual Network (VNet) is the service that integrates multiple virtual networks in Azure. It utilizes services such as Virtual Network Peering and VPN Gateways for connectivity both within the Azure cloud and with on-premises networks.
Step-by-step explanation:
The service in Azure that integrates multiple virtual networks is Azure Virtual Network (VNet). Azure VNet allows customers to create isolated networks within the Azure cloud, as well as securely link these with on-premises data centers. By using services like Virtual Network Peering and VPN Gateways, Azure VNets can be connected and networked together, allowing for intercommunication among resources located across different VNets or hybrid environments.
Virtual Network Peering is a mechanism that connects two VNets in the same region directly, through Microsoft's backbone network, without using a VPN gateway, which can result in high-bandwidth connections with low latencies. Likewise, VPN Gateways can connect VNets located in different regions or connect an Azure VNet with an on-premises network over the internet.
The integration of VNets enables advanced scenarios like complex routing, shared services, and more, embracing a multi-region, multi-account architecture that is generally required by large-scale implementations.