This topic lists frequently asked questions about Elastic IP addresses (EIPs) and corresponding solutions.

What is an Elastic IP address (EIP)?

An Elastic IP address is a public IP address resource that you can purchase and own independently. Currently, you can associate EIPs with ECS instances, private network 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 belong to VPC networks.

An EIP is also a type of NAT IP address that is located in the public network gateway of Alibaba Cloud, and is mapped to the associated cloud resource through NAT. After an EIP is associated with the cloud resource, the cloud resource can access the public network by using the EIP.

What are the benefits of EIPs?

EIPs have the following benefits:
  • Independently purchased and owned

    You can purchase an EIP as an independent resource, instead of purchasing it together with other computing or storage resources.

  • Flexible association

    You can associate an EIP with a cloud resource as needed and release the EIP whenever it is not needed.

  • Configurable network capabilities

    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 VPC and classic network
Can the IP address be independently held? Yes No
Can the IP address be associated with and disassociated from the ECS instance at any time? Yes No
Can the IP address be viewed on the ENI of the ECS instance? The IP address can be viewed on the ENI in the Cut-Through Mode or Multi-EIP to ENI Mode.

Classic network: Yes

VPC: No

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

Cause: Alibaba Cloud has noticed that you have been frequently creating and changing EIPs recently, which triggered security alerts to temporarily restrict your purchase of EIPs.

Solution: Make sure that you do not exceed the quota for created EIPs for your account in the next seven days. The restrictions 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 a created EIP?

Possible causes are as follows:
  • The EIP is not associated with any cloud resources.
  • 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 from port 80, you cannot access the EIP over port 80.
  • The EIP has an overdue payment.

How are newly created EIPs allocated?

By default, newly created EIPs are allocated at random. However, if you release EIPs too frequently, you are likely to be re-allocated with the released EIPs rather than new ones.

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

For a pay-as-you-go 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. Examples:

After you release a pay-by-traffic EIP instance at 10:30, you will receive a bill for traffic usage of the EIP instance between the hours of 10:00 and 11:00.

Why shall I set a peak bandwidth for a pay-as-you-go EIP that incurs fees on a pay-by-traffic basis?

For a pay-as-you-go EIP that incurs fees on a pay-by-traffic basis, we recommend that you set a peak bandwidth value to avoid incurring excessive charges related to outbound traffic.

Note that the peak bandwidth is not guaranteed for a pay-as-you-go EIP that incurs fees on a pay-by-traffic basis. For example, the peak bandwidth of a pay-by-traffic 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 peak bandwidth, you must purchase a pay-by-bandwidth EIP or shared bandwidth instead.

How many EIPs can I create under one account?

You can create up to 20 EIPs under one account. If you need 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.

How many EIP API calls can I make in one day?

Yes. The number of EIP API calls that you can make on a daily basis is limited. Each user can make up to 500 EIP API calls per day.

What cloud resources can I associate an EIP with?

Currently, you can associate an EIP with an ECS instance of the VPC network, a private network SLB instance of the VPC network, a secondary ENI of the VPC network, a NAT Gateway, or an HaVip.

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

If you have purchased a NAT bandwidth plan before January 26, 2018, you must use the NAT bandwidth plan to associate public IP addresses with the NAT gateway. To associate an EIP with the NAT gateway, open a ticket.

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

Possible causes are as follows:

  • An EIP can only be associated with an ECS instance of the VPC network. If an ECS instance is not in the VPC network, it cannot be associated with an EIP.
  • The regions of the EIP and the ECS instance are not the same.
  • 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 with a public IP address or associated with an EIP.

How do I view the EIP on the ENI of an ECS instance after I have associated the EIP with 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.

However, if you associate an EIP with a secondary ENI, you can select the cut-through mode or multi-EIP to ENI mode, which allows you to view the EIP in the network interface information of the operating system.
  • Cut-through mode

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

  • Multi-EIP to ENI mode

    In the multi-EIP to ENI mode, the private network function of the secondary ENI is still available. The EIPs are visible to the ENI. After the operating system is configured with a static IP address, you can run the ifconfig or ipconfig command to obtain the public IP address of the ENI. For more information, see Set the multi-EIP to ENI mode.

How do I use multiple EIPs for an ECS instance if each ECS instance can only be associated with one EIP?

You can use multiple EIPs for an ECS instance in the following ways:
  • Associate an EIP with a secondary ENI and associate the ENI with the ECS instance. The number of secondary ENIs that can be associated with an ECS instance varies according to the specification of the ECS instance. For more information, see Instance families.
  • If you associate the EIP with the secondary ENI in the NAT Mode, you can associate multiple EIPs with one secondary private IP address of the secondary ENI respectively. Then, you can associate the secondary ENI with the ECS instance. In this way, the ECS instance can use multiple EIPs. For more information, see Associate multiple EIPs with an ENI in the NAT mode.
  • If you associate the EIP with the secondary ENI in the Multi-EIP to ENI Mode, you can directly associate multiple EIPs with the secondary ENI. Then, you can associate the secondary ENI with the ECS instance. In this way, the ECS instance can use multiple EIPs. For more information, see Set the multi-EIP to ENI mode.