NAT Gateway is an enterprise-class Internet gateway that provides NAT proxy services (SNAT and DNAT) with of up to 10 Gbps forwarding capacity. It also features high-availability and better disaster recovery.

As an Internet gateway, public IP addresses are required to make NAT Gateway fucntion normally. You can bind an Elastic IP Address (EIP) to a NAT Gateway as a public IP to use.
 If your account has a purchased NAT bandwidth package before January 26, 2018, you still need to use the bandwidth package to provide public IPs. Open a ticket if you want to bind an EIP to NAT Gateway.