An Elastic Network Interface (ENI) is a virtual network interface that can be attached to an ECS instance in a VPC.


ENIs can be used in the following scenarios:

  • Deploying a high-availability cluster

    An ENI is suitable for high-availability architecture for multiple network interfaces on a single instance.

  • Providing a low-cost failover solution

    You can detach an ENI from a failed ECS instance and then attach it to another ECS instance to quickly redirect the failed instance’s traffic to a backup instance, thereby quickly restoring your services.

  • Managing the network with refined controls

    You can configure multiple ENIs for an instance in any Alibaba Cloud region. For example, you can use some ENIs for internal management and other ENIs for Internet business access, so as to isolate confidential data from business data. You can also configure specific security group rules for each ENI based on the source IP address, protocols, ports, and more to achieve secured traffic control.

ENI types

ENIs are classified into two types:

  • Primary ENI

    The ENI created by default upon the creation of an instance in a VPC. The life cycle of the primary ENI is the same as that of the instance, and you cannot remove the primary ENI from the instance.

  • Secondary ENI

    You can create a secondary ENI and attach it to an instance or detach it from the instance. Multiple private IPs are supported for each secondary ENI. The maximum number of ENIs that you can attach to one instance varies with the instance type. For more information, see Instance type families.

ENI attributes

The following table displays ENI attributes.

Attribute Quantity
Primary private IP addresses 1
MAC address 1
Security group Up to 5
Description 1
ENI name 1


ENIs have the following limitations:

  • By default, one account can own up to 100 ENIs per region. The quota increases with the membership level. If you require a higher quota, open a ticket.

  • The ECS instance must be in the same zone of the same region as the ENI, but they do not have to be in the same VSwitch.

  • The number of ENIs that can be attached to an ECS instance is determined by the instance type. For more information, see Instance type families.

  • Only I/O optimized instance types support ENIs.

  • Attaching multiple ENIs does not increase the instance bandwidth.

    Note The instance bandwidth capability varies with the instance type.

Related operations

For images that cannot identify ENIs, log on to the instance to configure the ENI.

Console operations

You can complete the following operations in the ECS console:

API operations

You can complete the following operations by using APIs: