Basic Concepts

EIP

An EIP is a static, public IP address.

An EIP can be directly accessed over the Internet. A private IP address is an IP address on a local area network (LAN) and cannot be routed through the Internet.

You can bind an EIP to an ECS in your subnet to enable the ECS to communicate with the Internet.

Each EIP can be used by only one ECS at a time. To enable servers across AZs in a VPC to share an EIP, use a NAT gateway.

SNAT Connections

An SNAT connection consists of a source IP address, source port, destination IP address, destination port, and a transport layer protocol. The source IP address is the EIP, and the source port is the EIP port. An SNAT connection uniquely identifies a session.

DNAT Connections

DNAT connections enable servers in a private network to share an EIP to provide services accessible from the Internet.