Binding an EIP to the Extension NIC of an ECS to Enable Internet Access

Scenarios

As shown in Figure 1, the ECS has two NICs, one primary NIC and one extension NIC. You can bind an EIP to the extension NIC of the ECS and configure policy-based routes to ensure that the ECS can access the Internet through the EIP.

Figure 1 Accessing the Internet through the EIP bound to the extension NIC

This section uses a Linux ECS as an example.

Step 1: Create Cloud Resources and Attach an Extension NIC

Create a VPC and two subnets in the VPC.
In this example, the primary and extension NICs of the ECS are in different subnets.

For details, see Creating a VPC and Subnet.
Create an ECS in the VPC subnet.
For details about how to purchase an ECS, see Purchasing an ECS.
Create a network interface and attach it to the ECS as an extension NIC.
When creating a network interface, select a different subnet from where the primary NIC is created. For details, see Creating a Network Interface.

Attach the network interface to the ECS. For details, see section Attaching a Network Interface to a Cloud Server.
Assign an EIP and bind it to the extension NIC of the ECS.
For details, see Assigning an EIP.

Bind the EIP to the extension NIC of the ECS. For details, see Binding an EIP to a Network Interface.

Step 2: Obtain the ECS Network Information

Before configuring policy-based routes for the extension NIC, you need to obtain the network information in Table 1.

**Table 1** Required ECS network information
Item	Primary NIC	Extension NIC
Private IP address of the NIC	192.168.11.42	192.168.17.191
Subnet gateway address	192.168.11.1	192.168.17.1

Obtain the private IP addresses of the ECS NICs.
1. Log in to the management console.
1. Click in the upper left corner and select the desired region and project.
1. Click Service List and choose Compute > Elastic Cloud Server.
2. In the ECS list, locate the target ECS and click its name.
  The Summary tab page of the ECS is displayed.
3. Click the Network Interfaces tab and view the private IP addresses of the primary and extension NICs of the ECS.
Obtain the gateway address of the subnet.
1. Log in to the management console.
1. Click in the upper left corner and select the desired region and project.
1. Click Service List and choose Compute > Elastic Cloud Server.
2. In the ECS list, locate the target ECS and click its name.
  The Summary tab page of the ECS is displayed.
1. In the ECS Information area, click the VPC name.
  The Virtual Private Cloud page is displayed.
2. In the VPC list and click the number in the Subnets column.
  The Subnets page is displayed.
3. In the subnet list, click the subnet name.
  The Summary page is displayed.
4. In the Gateway and DNS Information area, view the gateway address of the subnet.
  Figure 2 Viewing the gateway address of the subnet

Step 3: Configure Policy-based Routes for the Extension NIC

ECS Remotely log in to the ECS.
For details, see Logging In to an ECS.
Run the following command to query the route information of the NIC:
route -n
The following figure is displayed. In this figure:
- The destination of the route for the primary NIC is 192.168.11.0/24.
- The destination of the route for the extension NIC is 192.168.17.0/24.
Run the following command to query the NIC names of the ECS:
ifconfig
The following figure is displayed. Search for the NIC name based on the NIC address. In this figure:
- 192.168.11.42 is the IP address of the primary NIC, and the NIC name is eth0.
- 192.168.17.191 is the IP address of the extension NIC, and the NIC name is eth1.
Configure the default route for the ECS so that it can access the Internet through the extension NIC.
1. Run the following command to delete the default route of the primary NIC:
  route del -net 0.0.0.0 gw Subnet-gateway-IP-address dev NIC-name
  
  The parameters are described as follows:
  - 0.0.0.0: destination IP address, indicating that multiple IP addresses are matched. Do not change the value.
  - Subnet gateway IP address: Enter the subnet gateway address of the primary NIC collected in section Table 1.
  - NIC name: Enter the name of the primary NIC obtained in 3.
  Example command:
  
  route del -net 0.0.0.0 gw 192.168.11.1 dev eth0
  
  This operation will interrupt ECS traffic.
2. Run the following command to configure the default route for the extension NIC:
  route add default gw Subnet-gateway-IP-address
  
  The parameters are described as follows:
  
  Subnet gateway IP address: Enter the subnet gateway address of the extension NIC collected in section Table 1.
  
  Example command:
  
  route add default gw 192.168.17.1

Verify network connectivity.

Run the following command to check whether the ECS can access the Internet:

ping Public-IP-address-or-domain-name

Example command:

ping support.huaweicloud.com

If information similar to the following is displayed, the ECS can communicate with the Internet.

[root@ecs-a01 ~]# ping support.huaweicloud.com
PING hcdnw.cbg-notzj.c.cdnhwc2.com (203.193.226.103) 56(84) bytes of data.
64 bytes from 203.193.226.103 (203.193.226.103): icmp_seq=1 ttl=51 time=2.17 ms
64 bytes from 203.193.226.103 (203.193.226.103): icmp_seq=2 ttl=51 time=2.13 ms
64 bytes from 203.193.226.103 (203.193.226.103): icmp_seq=3 ttl=51 time=2.10 ms
64 bytes from 203.193.226.103 (203.193.226.103): icmp_seq=4 ttl=51 time=2.09 ms
...
--- hcdnw.cbg-notzj.c.cdnhwc2.com ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3004ms
rtt min/avg/max/mdev = 2.092/2.119/2.165/0.063 ms

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