This topic answers the frequently asked questions about Elastic IP Address (EIP).

What is an EIP?

An EIP is a public IP address that you can purchase and own independently. You can associate EIPs with Elastic Compute Service (ECS) instances, internal Server Load Balancer (SLB) instances, secondary Elastic Network Interfaces (ENIs), NAT Gateway instances, and High-Availability Virtual IP Addresses (HAVIPs). The ECS instances, private network SLB instances, and secondary ENIs must be deployed in Virtual Private Cloud (VPC) networks.

An EIP is also a type of Network Address Translation (NAT) IP address that is deployed in the public-facing gateway of Alibaba Cloud, and is mapped to the associated cloud resource through NAT. After an EIP is associated with a cloud resource, the cloud resource can access the Internet through the EIP.

What are the benefits of EIP?

EIP has the following benefits:
  • Independently purchased and owned

    You can purchase and hold an EIP as an independent resource. You do not need to purchase it together with other computing or storage resources.

  • Flexible association

    You can associate an EIP with a cloud resource or disassociate the EIP as needed.

  • Flexible bandwidth

    You can adjust the bandwidth of an EIP at any time. The new bandwidth takes effect immediately.

What are the differences between an EIP and an ECS public IP address?

The following table lists the differences between an EIP and an ECS public IP address.
Item EIP ECS public IP address
Supported networks VPC networks VPC and classic networks
Whether you can independently hold the IP address Yes No
Whether the IP address can be associated with and disassociated from an ECS instance as needed Yes No
Whether you can view the IP address on the ENI of the ECS instance You can view the IP address on the ENI in Cut-Through Mode or Multi-EIP to ENI Mode.

Classic networks: Yes

VPC networks: No

Why does the system prompt "eip frequent purchase" when I apply for an EIP?

Cause: Alibaba Cloud has noticed that you have been frequently applying for and changing EIPs recently, which triggers security alerts, and therefore temporarily restricts your purchase of EIPs.

Solution: Make sure that the number of EIPs that you apply for in the next seven days does not exceed your account quota. This way, the restriction will be automatically removed after seven days. For more information about how to view the quota of your account, see Manage quotas.

Why am I unable to access an EIP?

Possible causes:
  • The EIP is not associated with a cloud resource.
  • If the EIP is associated with an ECS instance, check the security policies of the ECS instance. For example, if the ECS instance is added to a security group that denies the access requests to port 80, you cannot access port 80 of the EIP.
  • The EIP has an overdue payment.

How are newly created EIPs assigned?

By default, newly created EIPs are assigned at random. However, if you release EIPs frequently, you may be re-assigned with the released EIPs instead of new ones.

Why are fees still incurred after I have already released a pay-as-you-go EIP?

For a pay-by-data-transfer EIP, the bill is generated within the next hour. You will receive the bill after the EIP is released. Upon its release, the system stops charging the EIP. Example:

After you release a pay-by-data-transfer EIP instance at 10:30, you will receive the bill for the data usage from 10:00 to 11:00.

Why should I set a maximum bandwidth for a pay-by-data-transfer EIP?

For a pay-by-data-transfer EIP, we recommend that you set a maximum bandwidth to avoid unnecessary fees that incur due to excessive outbound traffic.

Note that the maximum bandwidth is not guaranteed for a pay-by-data-transfer EIP. For example, if the maximum bandwidth of a pay-by-data-transfer EIP is set to 200 Mbit/s, the peak bandwidth may not necessarily reach 200 Mbit/s. If you want to use an EIP that functions at a guaranteed maximum bandwidth, you must purchase a pay-by-bandwidth EIP or an EIP bandwidth plan.

How many EIPs can I create under one account?

You can create up to 20 EIPs under one account. To create more EIPs, apply for a quota increase. For more information, see Manage quotas.

Can I associate an EIP with multiple cloud resources?

No. You can only associate an EIP with one cloud resource.

Is the number of EIP operations that I can call limited?

Yes. If you call the EIP API more than 500 times within one day, the system will set a low priority for your requests.

If an ECS instance is associated with an EIP, can I use the DNAT feature of NAT Gateway to provide service to the Internet?

No. Limits:
  • If an ECS instance is associated with an EIP, you cannot use the Destination Network Address Translation (DNAT) feature of NAT Gateway to provide service to the Internet.

    Before you can use the DNAT feature, you must disassociate the EIP from the ECS instance. After you disassociate the EIP, you can add DNAT entries to the ECS instance. For more information, see Unbind an Elastic IP address from a cloud instance and Create a DNAT entry.

  • If you have already added DNAT entries to an ECS instance, you cannot associate an EIP with the ECS instance.

    Before you can associate an EIP with the ECS instance, you must delete the DNAT entries. After you delete the DNAT entries, you can associate an EIP with the ECS instance. For more information, see Delete a DNAT entry and Bind an EIP to a NAT Gateway.

Note If you have added DNAT entries to an ECS instance that is associated with an EIP, the EIP prevails when the ECS instance communicates with the Internet.

What are the cloud resources with which I can associate EIPs?

You can associate EIPs with ECS instances, private network SLB instances, secondary ENIs, NAT Gateway instances, and HAVIPs. The ECS instances, private network SLB instances, and secondary ENIs must be deployed in VPC networks.

Why am I unable to associate an EIP with a NAT Gateway instance?

If you purchased a NAT bandwidth plan before January 26, 2018, you must use the NAT bandwidth plan to provide Internet IP addresses to the NAT Gateway instance. To associate an EIP with the NAT Gateway instance, submit a ticket.

Why am I unable to associate an EIP with an ECS instance?

Possible causes:

  • You can associate an EIP only with an ECS instance that is deployed in a VPC network. If the ECS instance is not deployed in a VPC network, you cannot associate an EIP with the ECS instance.
  • The region of the EIP is different from that of the ECS instance.
  • The status of the ECS instance does not support the association action. You can associate an EIP only with an ECS instance that is in the running or stopped status.
  • The ECS instance is already assigned to an Internet IP address or associated with another EIP.

Why am I unable to view the EIP on the ENI of an ECS instance after I disassociate the EIP from the ECS instance?

An EIP is configured on the Internet gateway and mapped to the private ENI of the ECS instance through NAT. Therefore, you cannot view the EIP on the private ENI of the ECS instance.

When you associate an EIP with a secondary ENI, you can select the cut-through mode or multi-EIP to ENI mode.
  • Cut-through mode

    In this mode, the EIP replaces the private IP address of the secondary ENI. The secondary ENI becomes a pure Internet network interface controller (NIC) and its private network function is no longer available. You can view the EIP on the ENI of the operating system and run the ifconfig or ipconfig command to obtain the Internet IP address of the ENI. For more information, see Set the cut-through mode.

  • Multi-EIP to ENI mode

    In this mode, the private network function of the secondary ENI is available. You can view the EIP on the ENI. After the operating system is configured with a static IP address, you can run the ifconfig or ipconfig command to obtain the Internet IP address of the ENI. For more information, see Set the multi-EIP to ENI mode.

How can I associate multiple EIPs with one ECS instance?

You can associate multiple EIPs with one ECS instance in the following ways:
  • Associate an EIP with a secondary ENI, repeat the preceding step, and then associate the secondary ENIs with an ECS instance. The number of secondary ENIs that can be associated with an ECS instance varies based on the specification of the ECS instance. For more information, see Instance families.
  • If you associate an EIP with a secondary ENI in NAT Mode, you can associate multiple EIPs with the secondary private IP address of the secondary ENI. Then, you can associate the secondary ENI with an ECS instance. For more information, see Associate multiple Elastic IP addresses with an ENI in the NAT mode.
  • If you associate an EIP with a secondary ENI in Multi-EIP to ENI Mode, you can associate multiple EIPs with the secondary ENI. Then, you can associate the secondary ENI with an ECS instance. For more information, see Set the multi-EIP to ENI mode.