Adding a DNAT Rule to a Public NAT Gateway to Enable Servers to Be Accessed by the Internet

Scenarios

When one or more servers in a VPC need to provide services accessible from the Internet, you can add DNAT rules for a public NAT gateway, as introduced in this section.

Operation Process

Preparations

Before using NAT gateways, you need to:

• Complete real-name authentication.
• Top up your account.

Step 1: Assign an EIP

1. Go to the Buy EIP page.
2. On the Buy EIP page, set the EIP name to EIP-A.

   You can configure other EIP parameters as required. For details, see Assigning an EIP.

3. Click Next.

   Return to the EIP list to view EIP-A you have assigned.

Step 2: Create a Public NAT Gateway

1. Go to the Buy Public NAT Gateway page.
2. On the Buy Public NAT Gateway page, configure required parameters.

   Table 1 Parameters for creating a public NAT gateway

   Parameter	Example	Description
   Region	CN North-Beijing4	The region where the public NAT gateway is located.
   Specifications	Small	The specifications of the public NAT gateway. The value can be Extra-large, Large, Medium, or Small. To view more details about specifications, click Learn more on the page.
   Name	public-nat-01	The name of the public NAT gateway. Enter up to 64 characters. Only letters, digits, underscores (_), hyphens (-), and periods (.) are allowed.
   VPC	VPC-A	The VPC that the public NAT gateway belongs to. The VPC cannot be changed after the public NAT gateway is created. NOTE: To allow traffic to pass through the public NAT gateway, a route pointing to the public NAT gateway in the VPC route table is required. When you create a public NAT gateway, a default route with the destination of 0.0.0.0/0 pointing to the public NAT gateway is automatically added to the default route table of the VPC. If the route table already has a route with the destination of 0.0.0.0/0, the default route that points to the public NAT gateway will fail to be added. In this case, manually add a route that points to the gateway or create a custom route table and add a route with the destination of 0.0.0.0/0 pointing to the gateway to the new route table.
   Subnet	Subnet-A01	The subnet that the public NAT gateway belongs to. The subnet must have at least one available IP address. The subnet cannot be changed once the public NAT gateway is created. The NAT gateway will be deployed in the selected subnet and work for the entire VPC where it is deployed. To enable communications over the Internet, add SNAT or DNAT rules.
   Enterprise Project	default	The enterprise project that the public NAT gateway belongs to. If you do not specify an enterprise project, the default enterprise project will be used. You can configure an enterprise project for a public NAT gateway only after the enterprise project function is enabled.
   Advanced Settings (Optional)	-	Click the drop-down arrow to configure advanced parameters of the public NAT gateway.
   SNAT Connection TCP Timeout (s)	900	The timeout period of a TCP connection established using the SNAT rule. If no data is exchanged within this period, the TCP connection will be closed. Value range: 40 to 7200
   SNAT Connection UDP Timeout (s)	300	The timeout period of a UDP connection established using the SNAT rule. If no data is exchanged within this period, the UDP connection will be closed. Value range: 40 to 7200
   SNAT Connection ICMP Timeout (s)	10	The timeout period of an ICMP connection established using the SNAT rule. If no data is exchanged within this period, the ICMP connection will be closed. Value range: 10 to 7200
   TCP TIME_WAIT (s)	5	How long the side that actively closed the TCP connection is in the TIME_WAIT state. Value range: 0 to 1800
   Description	Not required	Supplementary information about the public NAT gateway. Enter up to 255 characters. Angle brackets (<>) are not allowed.
   Tag	Not required	The identifier of the public NAT gateway. A tag is a key-value pair. You can add up to 20 tags to each NAT gateway.

3. Click Create Now. On the page displayed, confirm the public NAT gateway specifications.
4. Click Submit.

   On the Public NAT Gateways page, you can view the purchased public NAT gateway in the list.

Step 3: Add a Default Route Pointing to the Public NAT Gateway

1. Go to the route table list page.
2. On the Route Tables page, click Create Route Table in the upper right corner.

   VPC: Select the VPC that the public NAT gateway belongs to.

3. After the custom route table is created, click its name. The Summary page is displayed.
4. Click Add Route and configure parameters as follows:

   Destination: Set it to 0.0.0.0/0.

   Next Hop Type: Select NAT gateway.

   Next Hop: Select the created NAT gateway.

   Figure 1 Add Route
   
5. Click OK.

Step 4: Add a DNAT Rule

1. Go to the public NAT gateway list page.
2. On the displayed page, click the name of the public NAT gateway on which you need to add a DNAT rule.
3. On the public NAT gateway details page, click the DNAT Rules tab.
4. Click Add DNAT Rule.
5. Configure required parameters. For details, see Table 2.

   Table 2 Descriptions of DNAT rule parameters

   Parameter	Example	Description
   Scenario	VPC	Select VPC if your servers in a VPC will use the DNAT rule to share an EIP to provide services accessible from the Internet. Direct Connect/Cloud Connect: Select this scenario if your on-premises servers or servers in another VPC will use the DNAT rule to provide services accessible from the Internet.
   Port Type	Specific port	The port type. Specific port: The public NAT gateway forwards requests intended for the EIP over specified ports and protocol to specified ports of the destination cloud server. All ports: The public NAT gateway directs all requests received by the EIP to the private IP address of the destination cloud server.
   Protocol	TCP	The protocol can be TCP or UDP. This parameter is available if you select Specific port for Port Type. If you select All ports, this parameter is All by default.
   Public IP Address Type	EIP	The EIP of the public NAT gateway.
   Public Port	80-100	The port of the EIP used by the NAT gateway. The port number ranges from 1 to 65535. You can enter a specific port number or a port range, for example, 80 or 80-100.
   Instance Type	Server	The type of the instance that will be providing services accessible from the Internet. Possible values are: Server Virtual IP address Custom
   NIC	-	The network interface attached to the server.
   Private Port	80-100	The port of the server that provides services accessible from the Internet through the DNAT rule. This parameter is available if you select Specific port for Port Type. The port number ranges from 1 to 65535. You can enter a specific port number or a port range, for example, 80 or 80-100.
   Description	Not required	Supplementary information about the DNAT rule. Enter up to 255 characters. Angle brackets (<>) are not allowed.

6. Click OK.

After you add a DNAT rule, add rules to the security group associated with the servers to allow inbound traffic. Otherwise, the DNAT rule will not work. For details, see section "Adding a Security Group Rule" in the Virtual Private Cloud User Guide.

Step 5: Verify that the DNAT Rule Has Been Added

In the DNAT Rules tab, you can view the details of the DNAT rule and check whether the DNAT rule has been added.

If the rule status is Running, the DNAT rule is created.

Step 6: Verify Whether the Server in a VPC Can Be Accessed from the Internet Through the NAT Gateway

1. Go to the ECS list page.
2. Log in to ECS 02 with an EIP bound.
3. On ECS 02, ping the EIP (120.46.131.153) to check whether ECS 01 on the private network can be accessed by ECS 02 on the public network through the NAT gateway.