Linux ifconfig set ip

Linux ifconfig command

On some Unix-like operating systems, ifconfig is used to configure, or view the configuration of, a network interface.

This page covers the GNU/Linux version of ifconfig.

On modern Linux systems, the ip command has replaced ifconfig.

Description

ifconfig stands for «interface configuration.» It is used to view and change the configuration of the network interfaces on your system.

Running the ifconfig command with no arguments, like this:

. displays information about all network interfaces currently in operation. The output resembles the following:

Here, eth0, lo and wlan0 are the names of the active network interfaces on the system.

• eth0 is the first Ethernet interface. (Additional Ethernet interfaces would be named eth1, eth2, etc.) This type of interface is usually a NIC connected to the network by a category 5 cable.
• lo is the loopback interface. This is a special network interface that the system uses to communicate with itself.
• wlan0 is the name of the first wireless network interface on the system. Additional wireless interfaces would be named wlan1, wlan2, etc.

These are the traditional naming conventions for network interfaces under Linux; other operating systems may have different names. For instance, under many BSD operating systems, Ethernet interfaces are named em0, em1, etc. Check your configuration, or consult your documentation, to determine the exact names of your interfaces.

Viewing the configuration of all interfaces

If you’d like to view the configuration of all network interfaces on the system (not just the ones that are currently active), you can specify the -a option, like this:

This produces output similar to running ifconfig, but if there are any inactive interfaces on the system, their configuration is also shown.

Viewing the configuration of a specific interface

To view the configuration of a specific interface, specify its name as an option. For instance,

. displays the configuration of device eth0 only.

Enabling and disabling an interface

When a network interface is active, it can send and receive data; when it is inactive, it is not able to transmit or receive. You can use ifconfig to change the status of a network interface from inactive to active, or vice versa.

To enable an inactive interface, provide ifconfig with the interface name followed by the keyword up.

Enabling or disabling a device requires superuser permissions, so you either have to be logged in as root, or prefix your command with sudo to run it with superuser privileges.

For instance, if network interface eth1 is inactive, you can activate it with the command:

Similarly, you can disable an active network interface using the down keyword. For instance, to disable the wireless network interface wlan0, use the command:

Configuring an interface

ifconfig can be used at the command line to configure (or re-configure) a network interface. This is often unnecessary since this configuration is often handled by a script when you boot the system. If you’d like to do so manually, you need superuser privileges, so we’ll use sudo again when running these commands.

To assign a static IP address to an interface, specify the interface name and the IP address. For example, to assign the IP address 69.72.169.1 to the interface wlan0, use the command:

To assign a network mask to an interface, use the keyword netmask and the netmask address. For instance, to configure the interface eth1 to use a network mask of 255.255.255.0, the command would be:

To assign a broadcast address to an interface, use the keyword broadcast and the broadcast address. For instance, to configure the interface wlan1 to use a broadcast address of 172.16.25.98, the command would be:

These configurations can combined in a single command. For instance, to configure interface eth0 to use the static IP address 192.168.2.5, the network mask 255.255.255.0, and the broadcast address 192.168.2.7, the command would be:

These are the most commonly-used configuration options for ifconfig. A complete list is provided below.

What about DHCP?

ifconfig can only assign a static IP address to a network interface. If you want to assign a dynamic IP address using DHCP, use the dhclient command.

Syntax

Technical description

ifconfig is used to configure the system’s kernel-resident network interfaces. It is used at boot time to set up interfaces as necessary. After that, it is usually only needed when debugging, or when system tuning is needed.

If no arguments are given, ifconfig displays the status of the system’s active interfaces.

If a single interface argument is given, it displays the status of the given interface only.

If a single -a argument is given, it displays the status of all interfaces, even those that are «down» (inactive).

In all other cases, ifconfig configures an interface according to the options provided.

About address families

If the first argument after the interface name is recognized as the name of a supported address family, that address family is used for decoding and displaying all protocol addresses. Currently supported address families include, inet (TCP/IP; this is the default), inet6 (IPv6), ax25 (AMPR Packet Radio), ddp (Appletalk Phase 2), ipx (Novell IPX) and netrom (AMPR Packet Radio).

Options

-a	Display information for all network interfaces, even if they are down.
-s	Display a short list in a format identical to the command «netstat -i«.
-v	Verbose mode; display additional information for certain error conditions.
interface	The name of the interface. This is usually a driver name followed by a unit number, for example «eth0» for the first Ethernet interface. If your kernel supports alias interfaces, you can specify them with eth0:0 for the first alias of eth0. You can use them to assign a second address. To delete an alias interface, use ifconfig eth0:0 down. Note: for every scope (i.e., same net with address/netmask combination) all aliases are deleted, if you delete the first (primary).
up	This flag causes the interface to be activated. It is implicitly specified if an address is assigned to the interface.
down	This flag causes the driver for this interface to be shut down.
[—]arp	Enable (or disable, if the «—» prefix is specified) the use of the ARP protocol on this interface.
[—]promisc	Enable (or disable, if the «—» prefix is specified) the promiscuous mode of the interface. If promiscuous mode is enabled, all packets on the network will be received by the interface.
[—]allmulti	Enable or disable all-multicast mode. If multicast mode is enabled, all multicast packets on the network will be received by the interface.
metric N	This parameter sets the interface metric, which is used by the interface to make routing decisions. N must be an integer between 0 and 4294967295. If you’re not sure what a network metric is, or whether to change it, you can safely leave this setting alone.
mtu N	This parameter sets the MTU (maximum transfer unit) of an interface. This setting is used to limit the maximum packet size transferred by the interface. If you’re not sure about it, you can safely leave this setting alone.
dstaddr address	Set the remote IP address for a point-to-point link (such as PPP). This keyword is now obsolete; use the pointopoint keyword instead.
netmask address	Set the IP network mask for this interface. This value defaults to the usual class A, B or C network mask (as derived from the interface IP address), but it can be set to any value.
add address/prefixlen	Add an IPv6 address to an interface.
del address/prefixlen	Remove an IPv6 address from an interface.
tunnel aa.bb.cc.dd	Create a new SIT (IPv6-in-IPv4) device, tunnelling to the given destination.
irq address	Set the interrupt line used by this device. Not all devices can dynamically change their IRQ setting.
io_addr address	Set the start address in I/O space for this device.
mem_start address	Set the start address for shared memory used by this device. Only a few devices need this.
media type	Set the physical port or medium type to be used by the device. Not all devices can change this setting, and those that can vary in what values they support. Typical values for type are 10base2 (thin Ethernet), 10baseT (twisted-pair 10 Mbps Ethernet), AUI (external transceiver), etc. The special medium type of auto tells the driver to auto-sense the media. Again, not all drivers can do this.
[—]broadcast [address]	If the address argument is given, this sets the protocol broadcast address for this interface. Otherwise, it sets (or clear, if the «—» prefix is used) the IFF_BROADCAST flag for the interface.
[—]pointopoint [address]	This keyword enables the point-to-point mode of an interface, meaning that it is a direct link between two machines with nobody else listening on it. If the address argument is also given, set the protocol address of the other side of the link, just like the obsolete dstaddr keyword does. Otherwise, set or clear the IFF_POINTOPOINT flag for the interface.
hw class address	Set the hardware address of this interface, if the device driver supports this operation. The keyword must be followed by the name of the hardware class and the printable ASCII equivalent of the hardware address. Hardware classes currently supported include ether (Ethernet), ax25 (AMPR AX.25), ARCnet and netrom (AMPR NET/ROM).
multicast	Set the multicast flag on the interface. This should not normally be needed as the drivers set the flag correctly themselves.
address	The IP address to be assigned to this interface.
txqueuelen length	Set the length of the transmit queue of the device. It is useful to set this to small values for slower devices with a high latency (such as a connection over a modem, or over ISDN) to prevent fast bulk transfers from disturbing interactive traffic like telnet too much.

Examples

Running ifconfig with no options displays the configuration of all active interfaces.

Displays the configuration of all interfaces, both active and inactive.

View the network settings on the interface eth0, which (under Linux) is the first Ethernet adapter installed in the system.

Activate the network interface eth1.

Deactivate the network interface wlan0.

Configure the network interface wlan1 to use the static IP address 122.140.201.66.

Configure the network interface wlan0 to use the network mask 255.255.255.0.

Configure eth0 to use the static IP address 192.168.1.102 using the network mask 255.255.255.0, and the broadcast address 192.168.1.255.

Related commands

arp — Manipulate the system ARP cache.
dhclient — Communicate with a DHCP server to obtain a dynamic IP address.
ifup/ifdown — Enable/Disable a network interface.
ifquery — Parse information about a network interface.
ip — Display and manipulate information about routing, devices, policy routing and tunnels.
iwconfig — Configure a wireless network interface.
ping — Send ICMP ECHO_REQUEST packets to network hosts.
netstat — Print information about network connections, routing tables, interface statistics, masquerade connections, and multicast memberships.
route — Display and manipulate the IP routing table.

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15 Useful “ifconfig” Commands to Configure Network Interface in Linux

ifconfig in short “interface configuration” utility for system/network administration in Unix/Linux operating systems to configure, manage and query network interface parameters via command-line interface or in a system configuration scripts.

The “ifconfig” command is used for displaying current network configuration information, setting up an ip address, netmask, or broadcast address to a network interface, creating an alias for the network interface, setting up hardware address, and enable or disable network interfaces.

15 Useful ifconfig Commands

This article covers “15 Useful “ifconfig” Commands” with their practical examples, which might be very helpful to you in managing and configuring network interfaces in Linux systems.

Update: The networking command ifconfig is deprecated and replaced by the ip command (Learn 10 Examples of IP Command) in most Linux distributions.

1. View All Network Interface Settings

The “ifconfig” command with no arguments will display all the active interfaces details. The ifconfig command is also used to check the assigned IP address of a server.

2. Display Information of All Network Interfaces

The following ifconfig command with the -a argument will display information of all active or inactive network interfaces on the server. It displays the results for eth0, lo, sit0 and tun0.

3. View Network Settings of Specific Interface

Using interface name (eth0) as an argument with the “ifconfig” command will display details of the specific network interface.

4. How to Enable a Network Interface

The “up” or “ifup” flag with interface name (eth0) activates a network interface if it is not inactive state and allowing to send and receive information. For example, “ifconfig eth0 up” or “ifup eth0” will activate the eth0 interface.

5. How to Disable a Network Interface

The “down” or “ifdown” flag with interface name (eth0) deactivates the specified network interface. For example, the “ifconfig eth0 down” or “ifdown eth0” command deactivates the eth0 interface if it is in an inactive state.

6. How to Assign an IP Address to Network Interface

To assign an IP address to a specific interface, use the following command with an interface name (eth0) and ip address that you want to set. For example, “ifconfig eth0 172.16.25.125” will set the IP address to interface eth0.

7. How to Assign a Netmask to Network Interface

Using the “ifconfig” command with the “netmask” argument and interface name as (eth0) allows you to define a netmask to a given interface. For example, “ifconfig eth0 netmask 255.255.255.224” will set the network mask to a given interface eth0.

8. How to Assign a Broadcast to Network Interface

Using the “broadcast” argument with an interface name will set the broadcast address for the given interface. For example, the “ifconfig eth0 broadcast 172.16.25.63” command sets the broadcast address to an interface eth0.

9. How to Assign an IP, Netmask, and Broadcast to Network Interface

To assign an IP address, Netmask address, and Broadcast address all at once using the “ifconfig” command with all arguments as given below.

10. How to Change MTU for a Network Interface

The “mtu” argument sets the maximum transmission unit to an interface. The MTU allows you to set the limit size of packets that are transmitted on an interface. The MTU is able to handle a maximum number of octets to an interface in one single transaction.

For example, “ifconfig eth0 mtu 1000” will set the maximum transmission unit to a given set (i.e. 1000). Not all network interfaces support MTU settings.

11. How to Enable Promiscuous Mode

What happens in normal mode, when a packet is received by a network card, it verifies that it belongs to itself. If not, it drops the packet normally, but in the promiscuous mode is used to accept all the packets that flow through the network card.

Today’s network tools use the promiscuous mode to capture and analyze the packets that flow through the network interface. To set the promiscuous mode, use the following command.

12. How to Disable Promiscuous Mode

To disable promiscuous mode, use the “-promisc” switch that drops back the network interface in normal mode.

13. How to Add New Alias to Network Interface

The ifconfig utility allows you to configure additional network interfaces using the alias feature. To add the alias network interface of eth0, use the following command. Please note that 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.

Next, verify the newly created alias network interface address, by using the “ifconfig eth0:0” command.

14. How to Remove Alias to Network Interface

If you no longer required an alias network interface or you incorrectly configured it, you can remove it by using the following command.

15. How to Change the MAC address of Network Interface

To change the MAC (Media Access Control) address of an eth0 network interface, use the following command with the argument “hw ether“. For example, see below.

These are the most useful commands for configuring network interfaces in Linux, for more information and usage of the ifconfig command use the manpages like “man ifconfig” at the terminal. Check out some other networking utilities below.

Other Networking Utilities

• nmcli – a command-line client that is used to control NetworkManager and report network information.
• Tcmpdump – is a command-line packet capture and analyzer tool for monitoring network traffic.
• Netstat – is an open-source command-line network monitoring tool that monitors incoming and outgoing network packets traffic.
• ss (socket statistics) – a tool that prints network socket-related information on a Linux system.
• Wireshark – is an open-source network protocol analyzer that is used to troubleshoot network-related issues.
• Munin – is a web-based network and system monitoring application that is used to display results in graphs using rrdtool.
• Cacti – is a complete web-based monitoring and graphing application for network monitoring.

To get more information and options for any of the above tools, see the man pages by entering “man toolname” at the command prompt. For example, to get the information for the “netstat” tool, use the command “man netstat“.

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