This topic describes how to configure SNAT for a NAT gateway. SNAT allows Elastic Compute Service (ECS) instances that do not have public IP addresses to access the Internet.

Scenarios

The following scenario is used as an example. An enterprise has created a virtual private cloud (VPC) and a vSwitch on Alibaba Cloud. Multiple ECS instances are created in the vSwitch. The ECS instances are not assigned static public IP addresses, and are not associated with elastic IP addresses (EIPs). To meet business requirements, the ECS instances must access the Internet.

You can configure SNAT for a NAT gateway. SNAT allows ECS instances that do not have public IP addresses in a VPC to access the Internet by using the EIP that is associated with the NAT gateway. Scenarios

Prerequisites

  • An Alibaba Cloud account is created. For more information, see create an Alibaba Cloud account .
  • A VPC and a vSwitch are created. For more information, see Create a VPC and Create a vSwitch.
  • The VPC that you created meets the following requirements:
    • The VPC does not have a custom route whose destination CIDR block is 0.0.0.0/0. If the custom route exists, delete it.
    • If you want to configure SNAT as a Resource Access Management (RAM) user, make sure that the RAM user has access and read permissions on the VPC. Otherwise, contact the Alibaba Cloud account owner to acquire the permissions.

Procedure

Procedure

Step 1: Create a NAT gateway

  1. Log on to the NAT Gateway console.
  2. On the NAT Gateway page, click Create NAT Gateway.
  3. The first time you purchase an enhanced NAT gateway, you must create a service-linked role for NAT Gateway. At the bottom of the Create NAT Gateway panel, click Create in the Notes on Creating Service-linked Roles section. After the service-linked role is created, you can purchase a NAT gateway.
  4. In the Create NAT Gateway panel, set the following parameters and click Buy Now:
    • Region and Zone: Select the region where you want to deploy the NAT gateway.
    • Zone: Select the zone where you want to deploy the NAT gateway.
    • VPC ID: Select the VPC where you want to deploy the NAT gateway. After the NAT gateway is created, you cannot change the VPC where the NAT gateway is deployed.
    • VSwitch ID: Select the vSwitch to which the NAT gateway is attached.
    • Gateway Type: By default, Enhanced is selected.
    • Billing Method: Select a billing method for the NAT gateway.

      Only the pay-by-data-transfer billing method is supported. For more information, see Pay-by-data-transfer.

    • Billing Cycle: By default, By Hour is selected. Bills are generated on an hourly basis. If you use a NAT gateway for less than one hour, the usage duration is rounded up to one hour.
  5. On the Confirm Order page, confirm the configuration of the NAT gateway, select the service agreement, and then click Activate Now.
    When the message Order complete. appears, the purchase is completed.

After you create a NAT gateway, you can find the NAT gateway on the NAT Gateway page.

Step 2: Associate the NAT gateway with an EIP

A NAT gateway works as expected only when you associate an EIP with the NAT gateway. After you create a NAT gateway, you can associate EIPs with the NAT gateway.

  1. Log on to the NAT Gateway console.
  2. In the top navigation bar, select the region where the NAT gateway is deployed.
  3. On the NAT Gateway page, find the NAT gateway that you want to manage and click Associate Now in the Elastic IP Address column.
  4. In the Associate EIP dialog box, set the parameters and click OK. The following table describes the parameters.
    Parameter Description
    Resource Group Select the resource group to which the EIP belongs.
    EIPs Select the EIP that you want to associate with the NAT gateway.

    Purchase EIPs is selected in this example. The system automatically creates a pay-by-data-transfer EIP and associates the EIP with the NAT gateway.

    After you associate an EIP with the NAT gateway, the EIP is displayed in the Elastic IP Address column.

Step 3: Create an SNAT entry

You can create an SNAT entry for a NAT gateway. This way, the ECS instances that do not have public IP addresses in the VPC can access the Internet by using the EIP that is associated with the NAT gateway.

  1. Log on to the NAT Gateway console.
  2. In the top navigation bar, select the region where the NAT gateway is deployed.
  3. On the NAT Gateway page, find the NAT gateway and click Configure SNAT in the Actions column.
  4. On the SNAT Management tab, click Create SNAT Entry.
  5. On the Create SNAT Entry page, set the following parameters and click Confirm.
    Parameter Description
    SNAT Entry Specify whether you want to create an SNAT entry for an ECS instance or a vSwitch. Specify vSwitch: The ECS instances that are attached to the specified vSwitch use the EIP to access the Internet. This option is selected in this example.
    • Select VSwitch: Select a vSwitch from the drop-down list.
      Note If you select multiple vSwitches, the system creates multiple SNAT entries that use the same EIP.
    • VSwitch CIDR Block: displays the CIDR block of the vSwitch.
    Select Public IP Address Select a public IP address to access the Internet. You can select an EIP from the drop-down list. Use One IP Address is specified in this example.
    Entry Name Enter a name for the SNAT entry.

    The name must be 2 to 128 characters in length, and can contain letters, digits, periods (.), underscores (_), and hyphens (-). The name must start with a letter.

Step 4: Test the network connectivity

After you create an SNAT entry, you can test the network connectivity of the ECS instances. In this example, an ECS instance that runs a Linux operating system is used to test the network connectivity.
Note Make sure that the security group rule of the ECS instance allows the ECS instance to access the Internet. For more information, see Overview.
  1. Log on to an ECS instance that is attached to the vSwitch.
  2. To test the network connectivity, run the ping command to ping www.aliyun.com, the domain name of Alibaba Cloud. If you can receive echo reply packets, it indicates that the connection is established.
    The result shows that the ECS instance passes the connectivity test and can access the Internet. Test the network connectivity

FAQ

How many SNAT entries can I add to a NAT gateway?

By default, you can add up to 40 SNAT entries to a NAT gateway.

How many EIPs can I specify in an SNAT entry?

You can specify up to 64 elastic IP addresses (EIPs) in an SNAT entry. The quota cannot be increased.

For more information about SNAT, see FAQ about SNAT.