15 Practical Examples of the ifconfig Command in Linux

The ifconfig (interface configuration) command is a powerful utility in Linux used for managing and displaying network interface settings.

While it has been largely replaced by the ip command in newer Linux distributions, ifconfig remains an essential tool for network administrators and users who need to configure network interfaces manually.

Syntax of ifconfig

ifconfig [interface] [options]

• interface: Specifies the network interface to configure.
• options: Includes commands to enable, disable, modify, or inspect interface parameters.

If ifconfig is run without any arguments, it displays details of the active network interfaces on the system.

Practical Examples of ifconfig

Below are some common use cases of the ifconfig command:

1. Display Active Network Interfaces
2. Show All Network Interfaces (Including Inactive Ones)
3. View Details of a Specific Network Interface
4. Enable a Network Interface
5. Disable a Network Interface
6. Assign an IP Address to an Interface
7. Assign an IP Address with a Subnet Mask
8. Assign an IP Address Using CIDR Notation
9. Restart a Network Interface
10. Change the MAC Address of an Interface
11. Set the MTU (Maximum Transmission Unit) Value
12. Enable Promiscuous Mode
13. Disable Promiscuous Mode
14. Create an Alias Interface
15. Remove an Alias Interface

1. Display Active Network Interfaces

To see all currently active network interfaces and their details:

ifconfig

This command outputs information such as IP addresses, MAC addresses, and interface statistics.

2. Show All Network Interfaces (Including Inactive Ones)

To list both active and inactive network interfaces:

ifconfig -a

This is useful for troubleshooting inactive or down interfaces.

3. View Details of a Specific Network Interface

To check the configuration of a particular interface, such as ens33:

ifconfig ens33

This displays specific details like assigned IP addresses and network statistics.

4. Enable a Network Interface

To bring a network interface online:

ifconfig ens33 up

This is useful if the interface is down or disabled.

5. Disable a Network Interface

To deactivate a network interface:

ifconfig ens33 down

This will disconnect the interface from the network until re-enabled.

6. Assign an IP Address to an Interface

To manually set an IP address for an interface:

ifconfig ens33 192.168.1.110

This is useful for static IP configurations.

7. Assign an IP Address with a Subnet Mask

To set an IP address along with a subnet mask:

ifconfig ens33 192.168.1.100 netmask 255.255.255.0

This command ensures that the device operates within the specified subnet.

8. Assign an IP Address Using CIDR Notation

ifconfig ens33 192.168.1.100/24

CIDR notation simplifies network configuration by specifying the subnet mask in a compact form.

9. Restart a Network Interface

To restart a network interface, bringing it down and back up:

ifconfig ens33 down && ifconfig ens33 up

This is a common troubleshooting step when experiencing connectivity issues.

10. Change the MAC Address of an Interface

To modify the MAC address of an interface temporarily:

ifconfig ens33 hw ether 00:11:22:33:44:55

This can be useful for privacy or bypassing MAC address filtering on networks.

11. Set the MTU (Maximum Transmission Unit) Value

To adjust the MTU size for an interface:

ifconfig ens33 mtu 1500

This helps in optimizing network performance and troubleshooting fragmentation issues.

12. Enable Promiscuous Mode

To enable promiscuous mode, allowing the interface to capture all packets:

ifconfig ens33 promisc

This is used in network monitoring and packet capture tools like Wireshark.

13. Disable Promiscuous Mode

ifconfig ens33 -promisc

Turning off promiscuous mode ensures that the interface only processes packets intended for it.

14. Create an Alias Interface

To create an alias (ens33:1) with a new IP address:

ifconfig ens33:1 192.168.1.101/24

Network aliasing allows multiple IP addresses on a single physical interface.

15. Remove an Alias Interface

To delete an alias interface:

ifconfig ens33:1 down

Removing an alias can be necessary when decommissioning a temporary network configuration.

Conclusion

Although ifconfig is no longer the default tool for managing network interfaces in modern Linux distributions, it remains a valuable utility for users managing older systems or requiring simple interface configurations. Understanding and using ifconfig effectively can help in network troubleshooting, configuration, and security assessments.

For more advanced networking features, consider using the ip command, which offers greater functionality and flexibility.