Before using an ENI, you need to understand the following concepts:
Primary ENIs and Secondary ENIs
The ENI that is automatically created when a CVM is created in a VPC instance is the primary ENI.
ENIs created by users are secondary ENIs.
The primary ENI cannot be unbound, while secondary ENIs can.
Primary Private IP Addresses
When an ENI is created:
The primary private IP address of the primary ENI is randomly assigned, which can be modified.
The primary private IP address of the secondary ENI is randomly assigned or customized, which cannot be modified.
Secondary Private IP Addresses
A secondary private IP address is any private IP address other than the primary private IP address. You can configure secondary private IP addresses when you create or edit an ENI.
A secondary private IP address can be bound and unbound.
EIPs
EIPs are bound to the ENI private IP addresses one to one.
Security Groups
You can bind a security group or security groups to an ENI as required by your business.
MAC Addresses
An ENI has a globally unique MAC address.