Configuring Network Interfaces in CentOS (original) (raw)

Last Updated : 11 Jun, 2026

A network interface is a connection point between a computer and a network (private or public). It is typically implemented using a Network Interface Card (NIC), which can be physical hardware or software-based. For example, loopback addresses like 127.0.0.1 (IPv4) and ::1 (IPv6) are virtual interfaces used internally by the system.

• Network interfaces can be physical (hardware NIC) or virtual (loopback, VLAN, etc.)
• CentOS 9 uses NetworkManager with keyfile format instead of older ifcfg files
• Interfaces can be configured using Static IP (manual) or DHCP (automatic)
• Interface names are based on hardware location and type, making them predictable
• Configuration can be done via CLI (nmcli) or GUI (nmtui) tools

Network Interface naming

Network interface names are assigned based on both their physical and virtual characteristics.

1. Physical Interfaces

Physical interfaces are associated with actual hardware (NICs) installed in the system. Their names are based on the slot number and port number of the adapter.

**Format:

e

**Examples:

• **e0, e1: Single-port adapters
• **e0c, e0d: Multi-port adapters

2. Virtual Interfaces

Virtual interfaces are software-based and do not correspond to physical hardware. These are commonly used for internal communication or advanced networking setups like VLANs.

**VLAN Interface Format

-
-

• VLAN interfaces are created by combining a base interface name with a VLAN ID.

**Examples:

• e7-2
• ifgrp1-2

3. Interface group names

Interface groups are user-defined and must follow these rules:

• Must begin with a letter
• Spaces are not allowed
• Maximum length is 15 characters
• Must be unique (not already in use)

**Examples:

• web_ifgrp
• ifgrp3

Method 1: Network Configuration via Command Line (CentOS 9)

We will configure network interfaces for Static IP and DHCP using the command line. It is important to note that in older versions of CentOS (below 9), network configuration files used the ifcfg format, which is now deprecated.

• CentOS 9 uses the keyfile format, managed by NetworkManager.

Configuration of a static IP and DHCP

Step 1: List Available Network Devices

Before configuring the network, you need to identify available network interfaces.

**Command:

nmcli d

• **nmcli: Command-line tool for NetworkManager
• **d: Displays all network devices

**Output:

**Note: Before configuring the network, you need to identify available network interfaces.

Step 2: Locate Network Configuration Files

Access existing network configuration files stored by NetworkManager. There you can see the current information about your network.

**Command:

cd /etc/NetworkManager/system-connections
ls

• ****/etc/NetworkManager/system-connections:** Directory where keyfile-based configurations are stored
• **ls: Lists available configuration files

**Output:

Step 3: Configure Network Interface

In this step, we configure key network parameters such as IP address, gateway, DNS, and interface mode.

**Example 1: Set Static IP Address (IPv4 Address)

Assign a fixed IP address to the interface

**Command:

nmcli connection modify enp0s3 ipv4.addresses 10.0.2.15/24

• **connection modify: Modifies an existing connection
• **enp0s3: Interface name (may vary on your system)
• **ipv4.addresses: Sets the IP address
• ****/24:** Subnet mask (equivalent to 255.255.255.0)

**Output:

**Example 2: Set Gateway

Define the default gateway for outbound traffic

**Command:

nmcli connection modify enp0s3 ipv4.gateway 10.0.2.2

**Output:

**Example 3: Configure DNS Server

Set DNS server for domain name resolution

**Command:

nmcli connection modify enp0s3 ipv4.dns "8.8.8.8"

**For multiple DNS:

nmcli connection modify enp0s3 ipv4.dns "8.8.8.8 8.8.4.4"

• **ipv4.dns: Specifies DNS server(s)
• Multiple DNS values are separated by space

**Example 4: Set Interface Mode (Static or DHCP)

Define whether IP configuration is manual or automatic

**Static IP (Manual) Command:

nmcli connection modify enp0s3 ipv4.method manual

**DHCP (Automatic) Command:

nmcli connection modify enp0s3 ipv4.method auto

• **manual: Requires IP, gateway, DNS to be set manually
• **auto: Uses DHCP to automatically assign network settings

**Output:

Step 4: Restart Network Connection

Apply the changes by restarting the connection.

**Command:

nmcli connection down enp0s3
nmcli connection up enp0s3

• **connection down: Deactivates the network connection
• **connection up: Reactivates it with updated settings

**Output:

Step 5: Verify the Configuration

Ensure that the network settings have been applied correctly

**Command:

nmcli device show enp0s3

• Displays detailed information about the interface

**Output:

Method 2: GUI( Graphical user interface way)

CentOS also allows network configuration using a graphical interface through the nmtui tool. This is a terminal-based text GUI that simplifies setting IP addresses, gateways, DNS, and switching between static and DHCP modes.

Install NetworkManager TUI (if not installed)

Ensure the GUI tool is available for configuration

**Command:

sudo yum -y install NetworkManager-tui

• Installs the nmtui tool via the YUM package manager

• Now that the Network Manager tool is installed follow the below steps to set the interface through GUI.

Step 1: Open Network Manager (nmtui)

Open the text-based GUI interface for network management

**Command:

nmtui

• nmtui launches a terminal-based GUI for NetworkManager
• Provides menus to edit connections, activate interfaces, and set system hostname

**Output:

Step 2: Choose “Edit a Connection”

• Select “Edit a connection” and press Enter
• Choose your network interface (like enp0s3)
• Press Enter to edit

**Output:

**Note: Interface names may vary depending on your system. This menu allows configuration of IP address, gateway, DNS, and connection method (Static or DHCP)

Step 3: Configure Network Interface

Set IP address, gateway, DNS, and connection method through GUI

**For Static IP:

• **Set IPv4 Configuration: Manual

**Enter:

• IP Address (with subnet, like 10.0.2.15/24)
• Gateway (like 10.0.2.2)
• DNS servers (like 8.8.8.8, 8.8.4.4)

**Output:

**DHCP Configuration:

• Set IPv4 Configuration: Automatic
• No need to manually enter IP, gateway, or DNS

**Output:

**Note: Make sure to select the correct method depending on whether you want manual or automatic IP assignment

Step 4: Enable Required Options

Ensure the following options are enabled, these settings ensure stable and automatic network connectivity.

• **Automatically connect: Enables auto-connection at system boot
• **Available to all users: Optional but recommended for shared systems

**Output:

Step 5: Save and Apply Changes

Apply and persist all configuration changes

• Select OK to save changes in the nmtui interface
• Exit the nmtui tool

Step 6: Restart Network Connection

Apply the changes by restarting the connection

**Command:

service network restart

**Output:

Step 7: Verify the Configuration

Confirm that the network settings have been applied correctly

**Commands Using nmcli:

nmcli device show enp0s3

• **nmcli device show: Displays detailed information about the selected interface

**Commands Using ip:

ip addr show enp0s3

• **ip addr show: Shows IP addresses and network state