IP addresses of ECS instances within the classic network - Network| Alibaba Cloud Documentation Center

IP addresses are used to connect to ECS instances or their deployed services. ECS instances within the classic network can be assigned two types of IP addresses: internal IP addresses and public IP addresses.

Internal IP addresses

Each new ECS instance within the classic network is assigned an internal IP address for communication over the internal network. For more information about internal network communication, see Intranet.

Internal IP addresses can be used in the following scenarios:

Load balancing
Communication over the internal network between ECS instances within the same LAN
Communication over the internal network between an ECS instance and other cloud services such as OSS and ApsaraDB RDS within the same LAN

Public IP addresses

If you select a public network bandwidth greater than 0 Mbit/s when you purchase an ECS instance within the classic network, the system assigns a public IP address to the instance.

Public IP addresses can be used in the following scenarios:

Communication between ECS instances and the Internet
Communication between an ECS instance and other cloud services that are not within the same LAN

Note After the system assigns a public IP address, you cannot release or disassociate the public IP address. If you set the public bandwidth of an instance to 0 Mbit/s by downgrading configurations during renewal or changing the bandwidth of a pay-as-you-go instance, the instance cannot be connected to the Internet but the public IP address is retained.

Billing

Communication traffic generated by using internal IP addresses is free of charge.

You are billed only for outbound Internet traffic. For more information, see Public bandwidth.

Configurations

Internal IP addresses
The internal IP addresses of ECS instances within the classic network are assigned by the system and cannot be modified. Do not change an internal IP address within the operating system. Otherwise, communication within the internal network may be interrupted.
Public IP addresses
- If you select Assign Public IP Address when you create an ECS instance within the classic network, the system assigns a public IP address to the instance. For more information, see Create an instance by using the wizard.
- You can modify the public IP address within six hours after you create an instance. For more information, see Change the public IP address of an ECS instance.
- If you do not select Assign Public IP Address when you create an ECS instance within the classic network, you can assign a public IP address by modifying the outbound public bandwidth. For more information about how to modify the public bandwidth of a subscription ECS instance, see Modify the bandwidth configurations of subscription instances. For more information about how to modify the public bandwidth of a pay-as-you-go ECS instance, see Modify the bandwidth configurations of pay-as-you-go instances.

Multicasting and broadcasting

Internal IP addresses of ECS instances within the classic network do not support multicasting or broadcasting.