ifconfig

Configure and display network interface parameters for Linux systems.

Description

The ifconfig command is used to configure or display network interface parameters for the Linux kernel. Changes made with ifconfig are not persistent across reboots or interface restarts. To make permanent changes, you must edit the network configuration files.

Syntax

ifconfig [interface] [options] [address]

Parameters

add <address> : Set an IPv6 address for the network interface.
del <address> : Remove an IPv6 address from the network interface.
down : Deactivate the specified network interface.
hw <type> <address> : Set the hardware type and address (MAC) of the interface.
io_addr <address> : Set the I/O address for the network interface.
irq <address> : Set the IRQ for the network interface.
media <type> : Set the media type for the network interface.
mem_start <address> : Set the start address of the memory used by the interface.
metric <number> : Set the routing metric.
mtu <bytes> : Set the Maximum Transmission Unit (MTU) for the interface.
netmask <mask> : Set the subnet mask for the interface.
tunnel <address> : Create a tunnel address between IPv4 and IPv6.
up : Activate the specified network interface.
-broadcast <address> : Treat packets to this address as broadcast packets.
-pointopoint <address> : Establish a direct connection with another interface.
-promisc : Enable or disable promiscuous mode for the interface.
IP address : Specify the IP address for the interface.
interface : Specify the name of the network interface.

Examples

Display active network interface information:

[root@localhost ~]# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:16:3E:00:1E:51  
          inet addr:10.160.7.81  Bcast:10.160.15.255  Mask:255.255.240.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:61430830 errors:0 dropped:0 overruns:0 frame:0
          TX packets:88534 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:3607197869 (3.3 GiB)  TX bytes:6115042 (5.8 MiB)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:56103 errors:0 dropped:0 overruns:0 frame:0
          TX packets:56103 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:5079451 (4.8 MiB)  TX bytes:5079451 (4.8 MiB)

Explanation:

eth0: Represents the first network card. HWaddr is the physical (MAC) address, here 00:16:3E:00:1E:51.
inet addr: The IP address of the card, here 10.160.7.81. Bcast is the broadcast address, and Mask is the subnet mask.
lo: The loopback address, typically 127.0.0.1. Used for testing network software locally.
Line 1: Connection type (Ethernet) and MAC address.
Line 2: IP address, broadcast address, and subnet mask.
Line 3: UP (interface is active), RUNNING (cable connected), MULTICAST (supports multicast), MTU (Maximum Transmission Unit).
Lines 4-5: Statistics for received (RX) and transmitted (TX) packets.
Line 7: Statistics for received and transmitted bytes.

Activate or deactivate a network interface:

ifconfig eth0 up
ifconfig eth0 down

Be careful when disabling interfaces via SSH; you may lose connection.

Add or remove an IPv6 address:

ifconfig eth0 add 33ffe:3240:800:1005::2/64
ifconfig eth0 del 33ffe:3240:800:1005::2/64

Change the MAC address:

ifconfig eth0 hw ether 00:AA:BB:CC:dd:EE

Configure an IP address:

ifconfig eth0 192.168.2.10
ifconfig eth0 192.168.2.10 netmask 255.255.255.0
ifconfig eth0 192.168.2.10 netmask 255.255.255.0 broadcast 192.168.2.255

Enable or disable ARP:

ifconfig eth0 arp
ifconfig eth0 -arp

Set MTU:

ifconfig eth0 mtu 1500

Other examples:

ifconfig       # Display active interfaces
ifconfig -a    # Display all interfaces, including inactive ones
ifconfig eth0  # Display info for eth0 only