ifconfig
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.
The networking command ifconfig is deprecated and replaced by the IP command.
Example 1 :
# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0B:CD:1C:18:5A
inet addr:172.16.25.126 Bcast:172.16.25.63 Mask:255.255.255.224
inet6 addr: fe80::20b:cdff:fe1c:185a/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:2341604 errors:0 dropped:0 overruns:0 frame:0
TX packets:2217673 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:293460932 (279.8 MiB) TX bytes:1042006549 (993.7 MiB)
Interrupt:185 Memory:f7fe0000-f7ff0000
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:5019066 errors:0 dropped:0 overruns:0 frame:0
TX packets:5019066 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:2174522634 (2.0 GiB) TX bytes:2174522634 (2.0 GiB)
tun0 Link encap:UNSPEC HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
inet addr:10.1.1.1 P-t-P:10.1.1.2 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
Example 2:Display Information of All Network Interfaces
# ifconfig -a
eth0 Link encap:Ethernet HWaddr 00:0B:CD:1C:18:5A
inet addr:172.16.25.126 Bcast:172.16.25.63 Mask:255.255.255.224
inet6 addr: fe80::20b:cdff:fe1c:185a/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:2344927 errors:0 dropped:0 overruns:0 frame:0
TX packets:2220777 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:293839516 (280.2 MiB) TX bytes:1043722206 (995.3 MiB)
Interrupt:185 Memory:f7fe0000-f7ff0000
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:5022927 errors:0 dropped:0 overruns:0 frame:0
TX packets:5022927 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:2175739488 (2.0 GiB) TX bytes:2175739488 (2.0 GiB)
sit0 Link encap:IPv6-in-IPv4
NOARP MTU:1480 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
tun0 Link encap:UNSPEC HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
inet addr:10.1.1.1 P-t-P:10.1.1.2 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)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.
# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:0B:CD:1C:18:5A
inet addr:172.16.25.126 Bcast:172.16.25.63 Mask:255.255.255.224
inet6 addr: fe80::20b:cdff:fe1c:185a/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:2345583 errors:0 dropped:0 overruns:0 frame:0
TX packets:2221421 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:293912265 (280.2 MiB) TX bytes:1044100408 (995.7 MiB)
Interrupt:185 Memory:f7fe0000-f7ff0000How 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.
# ifconfig eth0 up OR # ifup eth0
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.
# ifconfig eth0 down OR # ifdown eth0
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.
# ifconfig eth0 172.16.25.125
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.
# ifconfig eth0 netmask 255.255.255.224
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.
# ifconfig eth0 broadcast 172.16.25.63
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.
# ifconfig eth0 172.16.25.125 netmask 255.255.255.224 broadcast 172.16.25.63
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.
# ifconfig eth0 mtu 1000
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.
# ifconfig eth0 promisc
How to Disable Promiscuous Mode
To disable promiscuous mode, use the “-promisc” switch that drops back the network interface in normal mode.
# ifconfig eth0 -promisc
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.
# ifconfig eth0:0 172.16.25.127
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.
# ifconfig eth0:0 down
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.
# ifconfig eth0 hw ether AA:BB:CC:DD:EE:FF
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.
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