Kingsoft Cloud-Documentation-Configure an elastic network interface

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Configure ENIs for instances that run CentOS

Open the configuration file of an ENI.

vi /etc/sysconfig/network-scripts/ifcfg-eth1

Press the I key to enter the edit mode and add the configuration information to the ENI configuration file. Example:
```
DEVICE=eth1  # The new ENI.
BOOTPROTO=dhcp
ONBOOT=yes
TYPE=Ethernet
```
Press the Esc key, enter :wq, and then press the Enter key to save the file and exit the edit mode.
Check the ENI configuration file and confirm the modification.
```
cat /etc/sysconfig/network-scripts/ifcfg-eth1
```
Start ETH1.
```
ifup eth1
```
If an error is reported, run the service network restart command to restart the network service.

Configure ENIs for instances that run Ubuntu or Debian

Open the configuration file of an ENI.
```
vi /etc/network/interfaces
```
Press the I key to enter the edit mode and add the configuration information to the ENI configuration file. Take ETH1 as an example:
```
auto eth0 
iface eth0 inet dhcp 

auto eth1 # The new ENI.
iface eth1 inet dhcp
```
Press the Esc key, enter :wq, and then press the Enter key to save the file and exit the edit mode.
Check the ENI configuration file and confirm the modification.
```
cat /etc/network/interfaces
```
Start ETH1.
```
ifup eth1
```

Configure routes for ENIs

Take ETH1 as an example.

Start ENIs.

i. Run the ifup [ENI name] command to start the dhclient process and initiate a DHCP request.
```
ifup eth1
```
Set the metric parameter of the default route for each ENI in the route table as needed.

i. Set the metric parameter based on the gateway address of the subnet where the target ENI resides. You can query the gateway address of subnets in the VPC console or on the target KEC instance. To query the gateway addresses of subnets on the target KEC instance, run the ip addr command.

To query the gateway address of subnets in the VPC console, go to the Subnet page, as shown in the following figure.
```
ip -4 route add default via 10.1.2.1 dev eth1 metric 1001
```
Run the preceding commands to map the gateway address and metric parameter for ETH1. The mappings are as follows:

eth1: gw: 10.1.2.1 metric: 1001

ii. Check whether the values in the Gateway and Metric columns are the same as configured to verify whether the configuration is successful.
```
[root@ecshost~ ]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 10.0.0.253 0.0.0.0 UG 0 0 0 eth0
0.0.0.0 10.1.2.1 0.0.0.0 UG 1001 0 0 eth1
10.0.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
10.0.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
169.254.0.0 0.0.0.0 255.255.0.0 U 1002 0 0 eth0
169.254.0.0 0.0.0.0 255.255.0.0 U 1003 0 0 eth1
```
Create route tables.

i. Create route tables.
```
ip -4 route add default via 10.1.2.1 dev eth1 table 1001
```
Note: We recommend that you keep the names of route tables the same as the metric values of the default routes for ENIs. In this example, 1001 is used.

ii. Check whether the route tables are created.
```
[root@ecshost~ ]# ip route list table 1001
default via 10.0.0.253 dev eth1
```

Create policy-based routes.

i. Create policy-based routes based on the private IP addresses of the ENI.

ip -4 rule add from 10.1.2.66 lookup 1001

ii. View the routing rules.

[root@ecshost~ ]# ip rule list
0: from all lookup local
32765: from 10.1.2.66 lookup 1001
32766: from all lookup main
32767: from all lookup default

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