Alibaba Cloud Express Connect is a service that enables high-bandwidth, reliable, secure, and private connections between different networks, such as VPC networks across regions, Alibaba Cloud accounts, and on-premise data centers1. It supports different connection methods, such as physical connections, virtual border routers, and Express Cloud Connect1.

Scenario A: Intranet communication between VPCs and Smart Access Gateway in customers different branch offices. This scenario can be achieved by using Express Cloud Connect, which is based on the hardware capacities of Smart Access Gateway and provides SD-WAN capabilities1. Express Cloud Connect allows you to connect your branch offices to Alibaba Cloud through a dedicated partner backbone network, and access VPC networks in all regions1.

Scenario B: Intranet communication between a VPC and servers in an external IDC. This scenario can be achieved by using physical connections, which are dedicated network connections between on-premise data centers and VPC networks1. You can lease a line from your ISP or work with an Alibaba Cloud partner to establish a physical connection to Alibaba Cloud1. This way, you can access VPC networks in all regions with high bandwidth and low latency1.

Scenario C: Intranet communication between two VPCs in different accounts and different CIDR Blocks. This scenario can be achieved by using peering connections, which are logical connections that enable communication between VPC networks2. Peering connections support cross-region and cross-account scenarios, and allow you to connect VPC networks with different CIDR blocks2. However, peering connections are not part of Alibaba Cloud Express Connect, but a separate service called Cloud Enterprise Network2.

Scenario D: Intranet communication between two VPCs under the same account in the same region. This scenario can also be achieved by using peering connections, which are logical connections that enable communication between VPC networks2. Peering connections support intra-region and same-account scenarios, and allow you to connect VPC networks with different CIDR blocks2. However, peering connections are not part of Alibaba Cloud Express Connect, but a separate service called Cloud Enterprise Network2. References: 1: Express Connect - Alibaba Cloud 2: Introduction to Cloud Enterprise Network - Alibaba Cloud Document Center