Each VPC-Connected ECS instance can communicate within an intranet by using a private IP address, or communicate over the Internet by using a public IP address.

Private IP addresses

Each VPC-Connected ECS instance is assigned a private IP address when it is created. That address is determined by the VPC and the CIDR block of the VSwitch to which the instance is connected.

A private IP address can be used in the following scenarios:
  • Load balancing
  • Communication among ECS instances within an intranet
  • Communication between an ECS instance and other cloud products (such as OSS and RDS) within an intranet

For more information, see Intranet.

Modify a private IP address

You can modify the private IP address of a VPC-Connected ECS instance in the ECS console. For more information, see Change the private IP of an ECS instance.

Public IP addresses

VPC-Connected ECS instances support two public IP address types:

  • NatPublicIp, which is assigned to a VPC-Connected ECS instance, can be released only, and cannot be disassociated from the instance.
  • Elastic public IP (EIP). For more information, see What is an EIP address.

When a VPC-Connected ECS instance accesses the Internet, its public IP address is mapped to its private IP address through network address translation (NAT). 

You cannot find a network interface for Internet access by running commands within the operating system.

NatPublicIp and EIP are applicable to different scenarios:
  • NatPublicIp: If you want to assign a public IP address to a VPC-Connected ECS instance when creating the instance, and do not want to retain the public IP address when the instance is released, you can use a NatPublicIp address.

  • EIP: If you want to keep a public IP address and associate it to any of your VPC-Connected ECS instances in the same region, you can use an EIP address.

Obtain a public IP address
  • NatPublicIp: When creating a VPC-Connected ECS instance, if you select Assign a public IP, a NatPublicIp is assigned to the instance when it is created.

  • EIP: You can apply for an EIP address and bind it to a VPC-Connected ECS instance. In this case, do not assign a NatPublicIp to an instance. For more information, see Apply for an EIP address.

Release a public IP address
  • NatPublicIp: When a NatPublicIp address is assigned to an instance, you can only release the IP address, but cannot disassociate it. Only a NatPublicIp address that is assigned to a Subscription instance can be released. For more information, see Renew for configuration downgrade.
  • EIP: If you do not need an EIP address, disassociate it from a VPC-Connected ECS instance and release it in the EIP console. For more information, see Unbind and release an EIP address.


You are billed for outbound Internet traffic usage only. For more information, see Billing of Internet bandwidth.