IPv4 and IPv6 Dual-Stack Network

What Is an IPv4 and IPv6 Dual-Stack Network?

An IPv4 and IPv6 dual-stack network allows your resources, such as ECSs, to use both IPv4 and IPv6 addresses for private and public network communications. Figure 1 shows how an IPv4 and IPv6 dual-stack network works.

Figure 1 An IPv4 and IPv6 dual-stack network

**Table 1** Steps for deploying a dual-stack network
Step	Description
1	If you enable IPv6 when adding a VPC subnet, an IPv6 CIDR block is automatically assigned to the subnet. You cannot customize the IPv6 CIDR block.
2	Subnets in the same VPC can communicate with each other by default. Network ACLs protect subnets, and security groups protect the instances in it. Subnets in different network ACLs are isolated from each other. To connect these subnets, you need to add inbound and outbound rules to allow traffic in and out of the subnets. Security groups are isolated from each other. If two instances are associated with different security groups, you need to add inbound and outbound rules to allow the instances to communicate with each other. As shown in Figure 1, if allow rules are configured for network ACLs Fw-A and Fw-B and security groups Sg-A and Sg-B, ECS-A and ECS-B can communicate with each other: Using private IPv4 addresses (192.168.0.10 and 192.168.1.20). Using IPv6 addresses (2407:c080:1200:2075::a and 2407:c080:1200:1668::b).
3	To enable instances to communicate with the Internet using IPv4 addresses, you need to buy an EIP and bind it to the instance. An EIP can be bound to only one instance. As shown in Figure 1, you can bind EIP-A to ECS-A and EIP-B to ECS-B so that ECS-A and ECS-B can communicate with the Internet.
4	To enable instances to communicate with the Internet using an IPv6 address, you need to add the IPv6 address to a shared bandwidth. You can add multiple IPv6 addresses to a shared bandwidth. As shown in Figure 1, you can add the IPv6 addresses of ECS-A and ECS-B to a shared bandwidth so that ECS-A and ECS-B can communicate with the Internet.

Notes and Constraints

The IPv4/IPv6 dual-stack function is free for now, but will be billed at a later date (price yet to be determined).
Only certain ECS specifications support IPv6 networks and can use IPv4/IPv6 dual-stack networks. You need to select such ECSs in supported regions.
To check which ECSs support IPv6:
- On the ECS console: Click Buy ECS. On the displayed page, view the ECS specifications.
  If there is the IPv6 parameter with the value of Yes, the ECS specifications support IPv6.

IPv4 and IPv6 Dual-Stack Application Scenarios

If your ECS supports IPv6, you can build an IPv4 and IPv6 dual-stack network. Table 2 shows where IPv4 and IPv6 dual-stack networks can be used.

**Table 2** Application scenarios of IPv4 and IPv6 dual-stack networks
Application Scenario	Scenario	Subnet	ECS
Private communication using IPv6 addresses	Your applications deployed on ECSs need to communicate with other systems (such as databases) through private networks using IPv6 addresses.	IPv4 CIDR block IPv6 CIDR block	Private IPv4 address: used for private communication IPv6 address: used for private communication.
Public communication using IPv6 addresses	Your applications deployed on ECSs need to provide services accessible from the Internet using IPv6 addresses.	IPv4 CIDR block IPv6 CIDR block	Private IPv4 address + IPv4 EIP: used for public network communication IPv6 address + shared bandwidth: used for public network communication
Public communication using IPv6 addresses	Your applications deployed on ECSs need to both provide services accessible from the Internet and analyze the access request data using IPv6 addresses.	IPv4 CIDR block IPv6 CIDR block

If your ECS flavor does not support IPv6 addresses, you can enable the IPv6 EIP function to allow communications using IPv6 addresses. For details, see Table 3.

**Table 3** Application scenarios of IPv6 EIPs
Application Scenario	Description	Subnet	ECS
Public communication using IPv6 addresses	Your applications deployed on ECSs need to provide services accessible from the Internet using IPv6 addresses.	IPv4 CIDR block	Private IPv4 address IPv4 EIP (with IPv6 function enabled): used for public communication using IPv4 and IPv6 EIPs

Figure 2 Application scenarios of IPv6 networks

Operation Guide on IPv6 Networks

Operations on an IPv6 network are similar to those on an IPv4 network. Only some functions are configured in a different way. Table 4 describes how you can build and use an IPv6 network.

**Table 4** Operation guide on IPv6 networks
Scenario	Description	Reference
Creating an IPv6 subnet	Select Enable for IPv6 CIDR Block when creating a subnet. An IPv6 CIDR block will be automatically assigned to the subnet. You cannot customize an IPv6 CIDR block. IPv6 cannot be disabled after the subnet is created. You can enable IPv6 for existing subnets.	Creating a Subnet for the VPC
Viewing in-use IPv6 addresses	In the subnet list, click the subnet name. On the displayed page, view in-use IPv4 and IPv6 addresses on the IP Addresses tab.	Viewing IP Addresses in a Subnet
Adding a security group rule (IPv6)	Add a security group rule with Type set to IPv6 and Source or Destination set to an IPv6 address or IPv6 CIDR block.	Adding a Security Group Rule
Adding a network ACL rule (IPv6)	Add a network ACL rule with Type set to IPv6 and Source or Destination set to an IPv6 address or IPv6 CIDR block.	Adding a Network ACL Rule (Default Effective Sequence)
Adding an IPv6 route to the VPC route table	Add a route with Destination and Next Hop set to an IPv4 or IPv6 CIDR block. If the destination is an IPv6 CIDR block, the next hop can only be an IP address in the same VPC as the IPv6 CIDR block. If the destination is an IPv6 CIDR block, the next hop type can only be ECS, extension NIC, or virtual IP address. They must also have IPv6 addresses.	Adding a Custom Route
Assigning a virtual IPv6 address	If IPv6 is enabled for a VPC subnet, you can set IP Address Type to IPv6 when assigning for a virtual IP address.	Assigning a Virtual IP Address