Overview

An elastic network interface (referred to as a network interface in this documentation) is a virtual network card. You can create and configure network interfaces and attach them to your instances (ECSs and BMSs) to obtain flexible and highly available network configurations.

Network Interface Types

A primary network interface is created together with an instance by default, and cannot be detached from the instance.
An extended network interface is created on the Network Interfaces console, and can be attached to or detached from an instance.

Application Scenarios

Flexible migration
You can detach a network interface from an instance and then attach it to another instance. The network interface retains its private IP address, EIP, and security group rules. In this way, service traffic on the faulty instance can be quickly migrated to the standby instance, implementing quick service recovery.
Traffic management
You can attach multiple network interfaces that belong to different subnets in a VPC to the same instance, and configure the network interfaces to carry the private network traffic, public network traffic, and management network traffic of the instance. You can configure access control policies and routing policies for each subnet, and configure security group rules for each network interface to isolate networks and service traffic.

Constraints on Using Network Interfaces

The number of network interfaces that can be attached to an ECS is determined by the ECS specifications. For details, see ECS Specifications.

**Table 1** Constraints on using different types of network interfaces
Network Interface Type	Creation	Attachment	Communication with External Networks	Communication with Public Service Zone
Primary network interface	Created along with the instance by default and cannot be created separately.	Cannot be detached from the instance.	Supported	Supported
Extension network interface	Can be created separately on the Network Interface console.	Can be attached to or detached from the instance.	Not supported. Policy-based routes need to be configured for external network access. How Do I Configure Policy-Based Routes for an ECS with Multiple NICs?	Not supported

Extension network interfaces cannot be used to directly access Huawei Cloud services, such as DNS. You can use VPC Endpoint (VPCEP) to access these services. For details, see Buying a VPC Endpoint for Accessing Interface VPC Endpoint Services.