What Is NAT Gateway?

Public NAT Gateways

A public NAT gateway enables cloud and on-premises servers in a private subnet to share an EIP to access the Internet or provide services accessible from the Internet. Cloud servers are ECSs and BMSs in a VPC. On-premises servers are servers in on-premises data centers that connect to a VPC through Direct Connect or Virtual Private Network (VPN). A public NAT gateway supports up to 20 Gbit/s of bandwidth.

Public NAT gateways offer source NAT (SNAT) and destination NAT (DNAT).

• SNAT translates private IP addresses into EIPs so that traffic from a private network can go out to the Internet.

  Figure 1 shows how an SNAT rule works.

  Figure 1 NAT gateway with an SNAT rule
  
• DNAT enables servers within an AZ or across AZs in a VPC to share an EIP to provide services accessible from the Internet. With an EIP, a NAT gateway forwards the Internet requests from only a specific port and over a specific protocol to a specific port of a server, or it can forward all requests to the server regardless of which port they originated on.

  Figure 2 shows how a DNAT rule works.

  Figure 2 NAT gateway with a DNAT rule
  

Private NAT Gateways

Private NAT gateways provide network address translation, allowing ECSs and BMSs in a VPC to communicate with servers in other VPCs or on-premises data centers. You can configure SNAT and DNAT rules for a NAT gateway to translate the source and destination IP addresses of originating packets into a transit IP address.

Specifically,

• SNAT enables servers within one AZ or across AZs in a VPC to share a transit IP address to access on-premises data centers or other VPCs.
• DNAT enables servers that share the same transit IP address in a VPC to provide services accessible from on-premises data centers or other VPCs.

Transit Subnet

A transit subnet is a transit network and is the subnet to which the transit IP address belongs.

Transit IP Address

A transit IP address is a private IP address that can be assigned from a transit subnet. Cloud servers in your VPC can share a transit IP address to access on-premises networks or other VPCs.

Transit VPC

A transit VPC is where a transit subnet belongs to.

Figure 3 Private NAT gateway

How Do I Access the NAT Gateway Service?