<p>This article describes the main functions of NAT gateway, including SNAT, DNAT, and bandwidth package.</p> <p><strong><span style="font-size:18px">SNAT</span></strong></p> <p>NAT gateway features SNAT to provide active Internet access ability for ECS instances in the VPC. At the same time, SNAT can protect the backend servers of the intranet from exposing to the Internet, and only allows external servers to access backend servers actively connected to the external servers.</p> <p><img src="https://obs-cn-shanghai.yun.pingan.com/pcp-portal/20201707111719-12d1a9c09555.png" style="height:525px; width:435px" /></p> <p><strong><span style="font-size:18px">DNAT</span></strong></p> <p>NAT gateway features DNAT, which can map the public IP addresses applied in the NAT gateway to ECS instances to allow ECS instances to provide services for or access the Internet.</p> <p>DNAT supports two modes, including IP mapping and port mapping.</p> <p>&bull;&nbsp;<strong>IP mapping</strong></p> <p>IP mapping maps the private IP to the public IP address to allow designated ECS instances to access the Internet through the designated public IP address.</p> <p><img src="https://obs-cn-shanghai.yun.pingan.com/pcp-portal/20201707111800-1e53150b931c.png" style="height:521px; width:437px" /></p> <p>&bull;&nbsp;<strong>Port mapping</strong></p> <p>Port mapping maps a port of the public IP address to the ECS of the intranet and allows the designated port of designated ECS instance to access the Internet through designated public IP address and port.</p> <p><img src="https://obs-cn-shanghai.yun.pingan.com/pcp-portal/20201707111818-114d077e9fef.png" style="height:531px; width:435px" /></p> <p><strong><span style="font-size:18px">Bandwidth Package</span></strong></p> <p>NAT gateway features bandwidth package and provides bandwidth sharing and multiplexing. Each bandwidth package supports a maximum of five public IP addresses.</p>