In this article, we want to teach you How To Use the ifconfig command on Linux.
The ifconfig command can be used from the command line either to assign an address to a network interface or to configure or display the current network interface configuration information.
It must be used at system startup to define the network address of each interface present on a machine.
Also, it can be used at a later time to redefine an interface’s address or other operating parameters.
The network interface configuration is held on the running system and must be reset at each system restart.
How To Use ifconfig command on Linux
To use the ifconfig command, you need to log in to your Linux server as a root user or a non-root user with sudo privileges.
Now follow the steps below to learn the usage of the ifconfig command on Linux.
Usage of the ifconfig command on Linux
To view all the active interfaces details and check the assigned IP address of a server, you can use the following command with no arguments:
In your output you will see something similar to this:
Output eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500 inet netmask broadcast inet6 2a04:9dc0:c1:144:0:1:907:c40b prefixlen 26 scopeid 0x0<global> inet6 fe80::216:3eff:fe76:a15a prefixlen 64 scopeid 0x20<link> ether 00:16:3e:76:a1:5a txqueuelen 1000 (Ethernet) RX packets 1586380 bytes 222116758 (211.8 MiB) RX errors 26061 dropped 0 overruns 0 frame 26061 TX packets 206445 bytes 32345008 (30.8 MiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536 inet 127.0.0.1 netmask 255.0.0.0 inet6 ::1 prefixlen 128 scopeid 0x10<host> loop txqueuelen 1000 (Local Loopback) RX packets 19 bytes 2360 (2.3 KiB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 19 bytes 2360 (2.3 KiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
Also, you can use the ifconfig command on Linux with the -a option to view information of all active or inactive network interfaces on the server:
Now, you can use the command below to display details of a specific network interface. For example:
To enable a network interface, you can use the following command with the “up” or “ifup” options. For example:
# ifconfig eth0 up Or # ifup eth0
This command will activate the eth0 network interface.
On the other hand, you can use the ifconfig command on Linux to disable a network interface with the “down” or “ifdown” options:
# ifconfig eth0 down Or # ifdown eth0
Next, you can assign an IP address to a network interface. For example:
ifconfig eth0 172.16.25.125
This will set the IP address to the eth0 network interface.
Also, you can assign a Netmask to a network interface. For example, you can set a netmask to a given interface eth0:
ifconfig eth0 netmask 255.255.255.224
You can assign a broadcast to a network interface too. For example, you can use the ifconfig command on Linux to set the broadcast address to an interface eth0:
ifconfig eth0 broadcast 172.16.25.63
At this point, you can use three commands in a single command to assign an IP, a Netmask, and broadcast to a network interface. For example:
ifconfig eth0 172.16.25.125 netmask 255.255.255.224 broadcast 172.16.25.63
To change the MAC address of a network interface you can use the following command with the “hw ether“ option. For example:
ifconfig eth0 hw ether AA:BB:CC:DD:EE:FF
Change MTU for a Network Interface with the ifconfig command
The maximum transmission unit (MTU) is the largest size frame or packet — in bytes or octets (eight-bit bytes) — that can be transmitted across a data link. It is mostly used in reference to packet size on an Ethernet network using the Internet Protocol (IP).
For example, you can use the ifconfig command on Linux to set the MTU to a given set (i.e. 1000):
ifconfig eth0 mtu 1000
Enable Promiscuous Mode with the ifconfig command
Promiscuous mode is a type of computer networking operational mode in which all network data packets can be accessed and viewed by all network adapters operating in this mode. It is a network security, monitoring, and administration technique that enables access to entire network data packets by any configured network adapter on a host system.
For example, to set the promiscuous mode for the eth0 network interface, use the following command:
ifconfig eth0 promisc
Also, you can disable the promiscuous mode with the command below:
ifconfig eth0 -promisc
Add New Alias to Network Interface
The ifconfig command allows you to configure additional network interfaces using the alias feature.
Note: the alias network address is in the same subnet mask.
For example, if your eth0 network ip address is 172.16.25.125, then the alias ip address must be 172.16.25.127.
To add the alias network interface of eth0, use the following command:
ifconfig eth0:0 172.16.25.127
You can verify your new alias network interface address with the command below:
Also, you can remove it with the command below:
ifconfig eth0:0 down
At this point, you learn How to Use the ifconfig command on Linux.
With the Linux commands you learn to assign an IP address, netmask, broadcast to a network interface and etc.
Hope you enjoy it.