If you want to allow IPv6 clients to access your IPv4 services, you can create an IPv6 Classic Load Balancer (CLB) instance and add IPv4 backend servers to the CLB instance. If your IPv4 services are deployed on an IPv4 CLB instance, you can add an IPv6 gateway to the IPv4 CLB instance and scale out backend servers as network traffic increases. This solution does not require changes to existing systems and allows you to migrate services to IPv6 CLB instances without impacts on the IPv4 services. After an IPv6 CLB instance is created, a public IPv6 address is assigned to the CLB instance. The IPv6 address is used to forward IPv6 requests.
Characteristics of IPv6 CLB instances
Switch from IPv4 to IPv6 without service interruptions
IPv6 CLB instances support backend servers that use IPv4 addresses. You can migrate services to IPv6 CLB instances without changes to existing systems.
When network traffic increases, you can add an IPv6 gateway to the CLB instance and scale out backend servers without impacts on the IPv4 services.
More secure and reliable workload deployment
You can configure a blacklist for CLB to block network traffic from malicious IP addresses.
You can also configure a whitelist for CLB to allow network traffic only from specified IP addresses.
Limits
Only Internet-facing CLB instances support IPv6.
For more information about the regions where IPv6 instances are supported, see Regions supported by CLB.
IPv6 packets have longer IP headers than IPv4 packets. When an IPv6 CLB instance uses a UDP listener, make sure that the following requirement is met: The maximum transmission unit (MTU) supported by the elastic network interface (ENI) that each backend server uses to communicate with CLB is equal to or greater than 1,200 bytes. Otherwise, oversized packets may be discarded. You must modify the MTU setting in the configuration files of some applications accordingly. TCP supports the Maximum Segment Size (MSS) announcement. You do not need to modify the configurations of applications if a CLB instance uses a TCP listener.