If you need to transmit data between two ECS instances in the same region, use an intranet connection. Intranet connections can also be used to connect any combination of ECS, RDS, SLB, and OSS if they are deployed in the same region. However, the network speed is limited to one gigabit of shared bandwidth for non I/O optimized instances.

Alibaba Cloud instances can communicate over an intranet. The instances use one gigabit of shared bandwidth for non I/O optimized instances, and 10 gigabits of shared bandwidth for I/O optimized instances, with no special restrictions. However, because the intranet is a shared network, the bandwidth may fluctuate.

The following table describes how to enable intranet communication between ECS instances across different network types, depending on the number of accounts and whether the target regions and security groups are the same or different.
Network type Accounts used Regions Security groups How to enable intranet communication
VPC, same VPC One account or multiple accounts Same Same Enabled by default.
Different Authorize security groups for each other.
VPC, different VPCs One account or multiple accounts Same Either the same or different Use Express Connect. For more information, see Application scenarios from Product Introduction to Express Connect.
Different Different
Classic One account Same Same Enabled by default.
Multiple accounts Either the same or different Authorize security groups for each other. For more information, see Scenarios of security groups.

Private IP addresses are used for intranet communication. You cannot change the private IP address of an instance of the Classic network type, but you can change the private IP address of a VPC-Connected ECS instance. Private and public addresses of ECS instances do not support virtual IP (VIP) configuration.

By default, instances of different network types cannot communicate with one another in one intranet. However, VPC provides the ClassicLink function, which allows you to link an ECS instance in the classic network to cloud resources in a VPC through the intranet.