How to configure the network to use DHCP in a Linux instance -

You can configure an Elastic Compute Service (ECS) Linux instance to obtain its network settings through Dynamic Host Configuration Protocol (DHCP). With DHCP, your instance automatically receives its IP address and related network configuration, which simplifies setup and prevents manual configuration errors.

You must configure DHCP before you create a custom image from an instance. If the instance uses a static IP address, new instances launched from that image inherit the same static configuration, which can cause IP address conflicts or network connectivity issues.

Quick reference

The following table lists the configuration file path and restart command for each supported distribution.

Distribution	Config file path	Restart command
Alibaba Cloud Linux 3	`/etc/sysconfig/network-scripts/ifcfg-eth0`	`sudo nmcli c reload` then `sudo nmcli d connect eth0`
Alibaba Cloud Linux 4	`/etc/NetworkManager/system-connections/*.nmconnection`	`sudo nmcli c reload` then `sudo nmcli d connect eth0`
Alibaba Cloud Linux 2	`/etc/sysconfig/network-scripts/ifcfg-eth0`	`sudo systemctl restart network`
CentOS 6	`/etc/sysconfig/network-scripts/ifcfg-eth0`	`sudo service network restart`
CentOS 7	`/etc/sysconfig/network-scripts/ifcfg-eth0`	`sudo systemctl restart network`
CentOS 8	`/etc/sysconfig/network-scripts/ifcfg-eth0`	`sudo nmcli c reload` then `sudo nmcli d connect eth0`
Ubuntu 16 and earlier	`/etc/network/interfaces`	`sudo systemctl restart networking` (Ubuntu 14: `sudo reboot`)
Ubuntu 18 and later	`/etc/netplan/*.yaml`	`sudo netplan apply`
Debian 11 and earlier	`/etc/network/interfaces`	`sudo systemctl restart networking`
Debian 12	`/etc/netplan/*.yaml`	`sudo netplan apply`
Red Hat 6	`/etc/sysconfig/network-scripts/ifcfg-eth0`	`sudo service network restart`
Red Hat 7	`/etc/sysconfig/network-scripts/ifcfg-eth0`	`sudo systemctl restart network`
Red Hat 8 and 9	`/etc/sysconfig/network-scripts/ifcfg-eth0`	`sudo nmcli c reload` then `sudo nmcli d connect eth0`
Red Hat 10	`/etc/NetworkManager/system-connections/*.nmconnection`	`sudo nmcli c reload` then `sudo nmcli d connect eth0`
SUSE and OpenSUSE	`/etc/sysconfig/network/ifcfg-eth0`	`sudo systemctl restart wicked`

Step 1: Log on to the ECS instance

This step applies to all distributions.

Go to ECS console - Instance. In the top navigation bar, select the target region and resource group.
Go to the details page of the target instance. Click Connect and select Workbench. Follow the prompts on the page to log on to the terminal.

Step 2: Configure DHCP

Select the section that matches your Linux distribution and version.

Alibaba Cloud Linux

Alibaba Cloud Linux 3

Edit the network configuration file.

sudo vi /etc/sysconfig/network-scripts/ifcfg-eth0

Set the following parameters, then save and exit.

BOOTPROTO=dhcp
DEVICE=eth0
ONBOOT=yes
TYPE=Ethernet

Restart the network service.
1. Reload all NIC configurations.
```
sudo nmcli c reload
```
2. Activate the network interface.
```
sudo nmcli d connect eth0
```

Alibaba Cloud Linux 4

Identify the active connection name. Example output: In this example, eth0 is the NAME of the active network connection.

sudo nmcli connection show --active

NAME  UUID                                  TYPE      DEVICE
eth0  1dd9a779-d327-56e1-8454-c65e2556c12c  ethernet  eth0
lo    0973d353-93a1-41f8-8b7b-5922ade582c6  loopback  lo

Find the configuration file for that connection. Replace <id_name> with the NAME from the previous step. Example output:

sudo find /etc/NetworkManager/system-connections/ -type f -exec grep -l "id=<id_name>" {} \;

/etc/NetworkManager/system-connections/1.nmconnection

Open the file and verify that method under [ipv4] is set to auto. Replace <network_configuration_file_path> with the path from the previous step.
```
sudo vi <network_configuration_file_path>
```
Restart the network service.
1. Reload all NIC configurations.
```
sudo nmcli c reload
```
2. Activate the network interface.
```
sudo nmcli d connect eth0
```

Alibaba Cloud Linux 2

Edit the network configuration file.

sudo vi /etc/sysconfig/network-scripts/ifcfg-eth0

Set the following parameters, then save and exit.

BOOTPROTO=dhcp
DEVICE=eth0
ONBOOT=yes
TYPE=Ethernet

Restart the network service.
```
sudo systemctl restart network
```

CentOS

CentOS 6

Edit the network configuration file.

sudo vi /etc/sysconfig/network-scripts/ifcfg-eth0

Set the following parameters, then save and exit.

BOOTPROTO=dhcp
DEVICE=eth0
ONBOOT=yes
TYPE=Ethernet

Restart the network service.
```
sudo service network restart
```

CentOS 7

Edit the network configuration file.

sudo vi /etc/sysconfig/network-scripts/ifcfg-eth0

Set the following parameters, then save and exit.

BOOTPROTO=dhcp
DEVICE=eth0
ONBOOT=yes
TYPE=Ethernet

Restart the network service.
```
sudo systemctl restart network
```

CentOS 8

Edit the network configuration file.

sudo vi /etc/sysconfig/network-scripts/ifcfg-eth0

Set the following parameters, then save and exit.

BOOTPROTO=dhcp
DEVICE=eth0
ONBOOT=yes
TYPE=Ethernet

Restart the network service.
1. Reload all NIC configurations.
```
sudo nmcli c reload
```
2. Activate the network interface.
```
sudo nmcli d connect eth0
```

Ubuntu

Ubuntu 16 and earlier

Edit the network configuration file.
```
sudo vi /etc/network/interfaces
```

Set the following parameters, then save and exit.

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet dhcp

Restart the network service.
- For Ubuntu 14, run sudo reboot to restart the system and apply the configuration.
- For other versions, run sudo systemctl restart networking.

Ubuntu 18 and later

Find the active network configuration file. Example output: Netplan applies configurations alphabetically. In this example, the last file, /etc/netplan/99-eth0.yaml, overrides earlier ones and is the active configuration.
```
ls /etc/netplan/*.yaml | sort
```
```
/etc/netplan/100-eth0.yaml
/etc/netplan/50-cloud-init.yaml
/etc/netplan/99-eth0.yaml
```
Edit the active configuration file. Replace <network_configuration_file_path> with the path from the previous step.
```
sudo vi <network_configuration_file_path>
```

Set the following parameters, then save and exit.

network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      dhcp4: yes
      dhcp6: no

Apply the configuration.
```
sudo netplan apply
```

Debian

Debian 11 and earlier

Edit the network configuration file.
If the interfaces file contains source /etc/network/interfaces.d/*, edit the network configuration in /etc/network/interfaces.d/<network_config_file>.
```
sudo vi /etc/network/interfaces
```

Set the following parameters, then save and exit.

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet dhcp

Restart the network service.
```
sudo systemctl restart networking
```

Debian 12

Find the active network configuration file. Example output: Netplan applies configurations alphabetically. In this example, the last file, /etc/netplan/99-eth0.yaml, overrides earlier ones and is the active configuration.
```
ls /etc/netplan/*.yaml | sort
```
```
/etc/netplan/100-eth0.yaml
/etc/netplan/50-cloud-init.yaml
/etc/netplan/99-eth0.yaml
```
Edit the active configuration file. Replace <network_configuration_file_path> with the path from the previous step.
```
sudo vi <network_configuration_file_path>
```

Set the following parameters, then save and exit.

network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      dhcp4: yes
      dhcp6: no

Apply the configuration.
```
sudo netplan apply
```

Red Hat

Red Hat 6

Edit the network configuration file.

sudo vi /etc/sysconfig/network-scripts/ifcfg-eth0

Set the following parameters, then save and exit.

BOOTPROTO=dhcp
DEVICE=eth0
ONBOOT=yes
TYPE=Ethernet

Restart the network service.
```
sudo service network restart
```

Red Hat 7

Edit the network configuration file.

sudo vi /etc/sysconfig/network-scripts/ifcfg-eth0

Set the following parameters, then save and exit.

BOOTPROTO=dhcp
DEVICE=eth0
ONBOOT=yes
TYPE=Ethernet

Restart the network service.
```
sudo systemctl restart network
```

Red Hat 8 and 9

Edit the network configuration file.

sudo vi /etc/sysconfig/network-scripts/ifcfg-eth0

Set the following parameters, then save and exit.

BOOTPROTO=dhcp
DEVICE=eth0
ONBOOT=yes
TYPE=Ethernet

Restart the network service.
1. Reload all NIC configurations.
```
sudo nmcli c reload
```
2. Activate the network interface.
```
sudo nmcli d connect eth0
```

Red Hat 10

Identify the active connection name. Example output: In this example, eth0 is the NAME of the active network connection.

sudo nmcli connection show --active

NAME  UUID                                  TYPE      DEVICE
eth0  1dd9a779-d327-56e1-8454-c65e2556c12c  ethernet  eth0
lo    0973d353-93a1-41f8-8b7b-5922ade582c6  loopback  lo

Find the configuration file for that connection. Replace <id_name> with the NAME from the previous step. Example output:

sudo find /etc/NetworkManager/system-connections/ -type f -exec grep -l "id=<id_name>" {} \;

/etc/NetworkManager/system-connections/1.nmconnection

Open the file and verify that method under [ipv4] is set to auto. Replace <network_configuration_file_path> with the path from the previous step.
```
sudo vi <network_configuration_file_path>
```
Restart the network service.
1. Reload all NIC configurations.
```
sudo nmcli c reload
```
2. Activate the network interface.
```
sudo nmcli d connect eth0
```

SUSE and OpenSUSE

Edit the network configuration file.

sudo vi /etc/sysconfig/network/ifcfg-eth0

Set the following parameters, then save and exit.
```
BOOTPROTO='dhcp'
STARTMODE='auto'
```
Restart the network service.
```
sudo systemctl restart wicked
```

Verify the configuration

After you restart the network service, verify that the instance obtained an IP address through DHCP.

Run the following command to check the IP address assigned to the network interface:

ip addr show eth0

In the output, look for an inet line that shows the assigned IP address. If an IP address is displayed, DHCP is working correctly.

You can also check network connectivity:

ping -c 4 100.100.2.136

A successful response confirms that the instance can communicate over the network.