Help Center/ Elastic Cloud Server/ Drawer/ Purchasing an ECS/ Network Configurations/ Network Parameters
Updated on 2025-10-30 GMT+08:00
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Network Parameters

Description

  • VPC

    Virtual Private Cloud (VPC) allows you to create logically isolated, configurable, and manageable virtual networks for ECSs. You can define security groups, virtual private networks (VPNs), CIDR blocks and bandwidth for a VPC. This makes it easy for you to manage and configure private networks and improves network security. It improves resource security and simplifies network deployment on the cloud.

    ECSs in different VPCs cannot communicate with each other by default.

  • Subnet

    A subnet is a unique CIDR block with a range of IP addresses in a VPC. All resources in a VPC must be deployed on subnets. Subnets in a VPC cannot overlap with each other.

    By default, all instances in different subnets of the same VPC can communicate with each other and the subnets can be located in different AZs. If you have a VPC with two subnets in it and the subnets are located in different AZs, they can communicate with each other by default.

    Figure 1 Subnet
  • NIC

    A network interface card (NIC) is a virtual network adapter that can be bound to an ECS in a VPC. You can manage the ECS network with a NIC. A NIC can be a primary NIC or an extension NIC.

    The number of extension NICs that can be attached to an ECS is determined by the ECS specifications.

    Table 1 NICs

    Type

    Creation

    Attachment

    Communication with External Networks

    Communication with Public Service Zone

    Primary NIC

    Created along with the instance by default and cannot be created separately.

    Cannot be detached from the instance.

    Supported

    Supported

    Extension NIC

    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
  • IPv4

    By default, IPv4 addresses only support communication over private networks. You can configure an EIP or a public NAT gateway to enable communication over public networks. For details, see Binding an EIP and Using a Public NAT Gateway to Enable Servers to Share One or More EIPs to Access the Internet.

  • IPv6

    IPv6 addresses can effectively address the issue of limited IPv4 address resources. Once IPv6 is enabled, the instance can run in dual-stack mode, which means the instance has two versions of IP addresses: IPv4 and IPv6. They both can be used to access the private and public networks.

FAQs

Will I Be Billed for Using the VPC Service?

The VPC service is free of charge, but you need to pay for the bandwidth you use.

Can Subnets Communicate with Each Other?

Subnets in the same VPC can communicate with each other, but those in different VPCs cannot by default. You can create VPC peering connections to enable subnets in different VPCs to communicate with each other.

For more information, see VPC Help Center.

What Can I Do If My ECS with Multiple NICs Cannot Communicate with the Network?

Generally, the default route of an OS will preferentially select the primary NIC. If an extension NIC is selected in a route and the network malfunctions, this issue is typically caused by incorrect route configuration.

  • If the ECS has multiple NICs, check whether the default route is available.
    1. Log in to the ECS and run the following command to check whether the default route is available:

      ip route

      Figure 2 Default route
    2. If the route is unavailable, run the following command to add it:

      ip route add default via XXXX dev eth0

      In the preceding command, XXXX specifies a gateway IP address.

Parent Topic: Network Configurations