An elastic IP address (EIP) is a public IP address that you can purchase and use as an independent resource. EIPs can be retained independently and associated with or disassociated from Elastic Compute Service (ECS) instances in virtual private clouds (VPCs).


EIPs are NAT IP addresses that are located in the public gateway of Alibaba Cloud. By means of NAT, EIPs are mapped to the primary elastic network interfaces (ENIs) of the ECS instances that are associated with the EIPs. You can associate EIPs with ECS instances that are located in VPCs to enable the instances to communicate over the Internet. Similar to system-assigned public IP addresses (PublicIP addresses), EIPs remain invisible inside the operating systems of ECS instances.

Differences between EIPs and public IP addresses

ECS instances located in VPCs support both public IP addresses and EIPs. The following table describes the differences between EIPs and public IP addresses in several aspects.

Item PublicIP address EIP
Scenario If you want an instance to have a public IP address that will not be retained when the instance is released, you can configure a PublicIP address to be automatically assigned when you create the instance. If you want to retain a public IP address after its associated instance is released for use with other ECS instances, use an EIP. Each EIP can be associated with or disassociated from different ECS instances. After an instance is released, its associated EIP is retained.
Description If you select Assign Public IPv4 Address when you create an ECS instance, a PublicIP address is assigned to the instance. After an EIP is created, it can be associated with an ECS instance that is not assigned a PublicIP address. For more information, see Apply for an EIP and Associate an EIP with an instance.
Maximum number of IP addresses that can be assigned to or associated with a single ECS instance Only a single PublicIP address can be assigned to each ECS instance. Multiple EIPs can be associated with a single ECS instance in multi-EIP-to-ENI mode. For more information, see Associate EIPs with secondary ENIs in multi-EIP-to-ENI mode (new applications are not accepted).
Method to disassociate an IP address After a PublicIP address is assigned to an ECS instance, the address can only be released along with the instance but cannot be disassociated from the instance. You can convert PublicIP addresses into EIPs as needed. EIPs can be associated with or disassociated from ECS instances at any time. For more information, see Convert the public IP address of a VPC-type instance to an EIP. EIPs can be disassociated from ECS instances. For more information, see Disassociate an EIP from an instance.
Method to release an IP address For more information, see Release a pay-as-you-go EIP.
Method to view a media access control (MAC) address ECS instances in VPCs are connected to the Internet by using the mapping of public IP addresses to internal network interface controllers (NICs). Therefore, the public NICs of ECS instances in VPCs cannot be discovered from within the instances regardless of whether the instances are assigned PublicIP addresses or associated with EIPs.

Billing methods

EIPs support the subscription and pay-as-you-go billing methods. For more information, see Overview.


EIPs can be associated with ECS instances or ENIs. An EIP can be associated only with an ECS instance that meets the following requirements:

  • The ECS instance is located in a VPC.
  • The ECS instance is located in the same region as the EIP.
  • The ECS instance is in the Running or Stopped state.
  • No public IP addresses are associated with the primary ENI of the ECS instance.


For more information, see EIP overview.