ifconfig - Unix, Linux Command

NAME

ifconfig - configure a network interface

SYNOPSIS

ifconfig [interface]
ifconfig interface [aftype] options | address ...

DESCRIPTION

Ifconfig is used to configure the 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 currently 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. Otherwise, it configures an interface.

OPTIONS

TAG	DESCRIPTION
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.
down	This flag causes the driver for this interface to be shut down.
[-]arp	Enable or disable the use of the ARP protocol on this interface.
[-]promisc	Enable or disable the promiscuous mode of the interface. If selected, all packets on the network will be received by the interface.
[-]allmulti	Enable or disable all-multicast mode. If selected, all multicast packets on the network will be received by the interface.
metric N	This parameter sets the interface metric. It is not available under GNU/Linux.
mtu N	This parameter sets the Maximum Transfer Unit (MTU) of an interface.
dstaddr addr	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 addr	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 addr/prefixlen	Add an IPv6 address to an interface.
del addr/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 addr	Set the interrupt line used by this device. Not all devices can dynamically change their IRQ setting..
io_addr addr	Set the start address in I/O space for this device..
mem_start addr	TSet the start address for shared memory used by this device. Only a few devices need this..
[-]broadcast [addr]	If the address argument is given, set the protocol broadcast address for this interface. Otherwise, set (or clear) the IFF_BROADCAST flag for the interface..
[-]pointopoint [addr]	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.
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 (modem links, ISDN) to prevent fast bulk transfers from disturbing interactive traffic like telnet too much

EXAMPLES

EXAMPLE-1:

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

# ifconfig

output:
# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:0c:29:9b:49:bc
          inet addr:192.168.134.128  Bcast:192.168.134.255  Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fe9b:49bc/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:11545 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6177 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:923360 (923.3 KB)  TX bytes:1712607 (1.7 MB)

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:65536  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)

virbr0    Link encap:Ethernet  HWaddr 3a:bf:4c:fb:90:b6
          inet addr:192.168.122.1  Bcast:192.168.122.255  Mask:255.255.255.0
          UP BROADCAST 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:0
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

EXAMPLE-2:

To Display Information of All Network Interfaces:

# ifconfig -a

output:

# ifconfig -a
eth0      Link encap:Ethernet  HWaddr 00:0c:29:9b:49:bc
          inet addr:192.168.134.128  Bcast:192.168.134.255  Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fe9b:49bc/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:11545 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6177 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:923360 (923.3 KB)  TX bytes:1712607 (1.7 MB)

eth1      Link encap:Ethernet  HWaddr 00:0c:29:8b:89:bc
          inet addr:  Bcast:  Mask:
          inet6 addr: fe80::20c:29ff:fe9b:49bc/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:11545 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6177 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:923360 (923.3 KB)  TX bytes:1712607 (1.7 MB)

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:65536  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)

virbr0    Link encap:Ethernet  HWaddr 3a:bf:4c:fb:90:b6
          inet addr:192.168.122.1  Bcast:192.168.122.255  Mask:255.255.255.0
          UP BROADCAST 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:0
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

EXAMPLE-3:

To View Network Settings of Specific Interface:

# ifconfig eth0

output:
# ifconfig eth0
eth0      Link encap:Ethernet HWaddr 00:0c:29:9b:49:bc
          inet addr:192.168.134.128 Bcast:192.168.134.255 Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fe9b:49bc/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
          RX packets:11696 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6223 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:933886 (933.8 KB) TX bytes:1720687 (1.7 MB)

EXAMPLE-4:

The “up” or “ifup” flag with interface name (eth1) activates an network interface:

# ifconfig eth1 up
OR
# ifup eth1

output:
# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0c:29:9b:49:bc

          inet addr:192.168.134.128  Bcast:192.168.134.255  Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fe9b:49bc/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:11545 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6177 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:923360 (923.3 KB)  TX bytes:1712607 (1.7 MB)

eth1      Link encap:Ethernet  HWaddr 00:0c:29:9b:49:bc
          inet addr:192.168.134.129  Bcast:192.168.134.255  Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fe9b:49bc/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:11545 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6177 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:923360 (923.3 KB)  TX bytes:1712607 (1.7 MB)


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:65536  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)

virbr0    Link encap:Ethernet  HWaddr 3a:bf:4c:fb:90:b6
          inet addr:192.168.122.1  Bcast:192.168.122.255  Mask:255.255.255.0
          UP BROADCAST 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:0
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

EXAMPLE-5:

The “down” or “ifdown” flag with interface name (eth1) deactivates the specified network interface:

# ifconfig eth1 down
OR 
# ifdown eth1

output:

# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0c:29:9b:49:bc

          inet addr:192.168.134.128  Bcast:192.168.134.255  Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fe9b:49bc/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:11545 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6177 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:923360 (923.3 KB)  TX bytes:1712607 (1.7 MB)


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:65536  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)

virbr0    Link encap:Ethernet  HWaddr 3a:bf:4c:fb:90:b6
          inet addr:192.168.122.1  Bcast:192.168.122.255  Mask:255.255.255.0
          UP BROADCAST 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:0
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

EXAMPLE-6:

To assign an IP address to an specific interface:

# ifconfig eth1 192.168.134.129

output:
# ifconfig eth1

eth1 Link encap:Ethernet HWaddr 00:0c:29:9b:49:bc

          inet addr:192.168.134.129  Bcast:192.168.134.255  Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fe9b:49bc/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:11545 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6177 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:923360 (923.3 KB)  TX bytes:1712607 (1.7 MB)

EXAMPLE-7:

To Assign a Netmask to Network Interface:

# ifconfig eth0 netmask 255.255.255.224

output:
# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:0c:29:9b:49:bc

          inet addr:192.168.134.128  Bcast:192.168.134.255  Mask:255.255.255.224
          inet6 addr: fe80::20c:29ff:fe9b:49bc/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:11545 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6177 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:923360 (923.3 KB)  TX bytes:1712607 (1.7 MB)

EXAMPLE-8:

* To Assign a IP, Netmask and Broadcast to Network Interface:

# ifconfig eth0 172.16.25.125 netmask 255.255.255.224 broadcast 172.16.25.63

output:
# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:0c:29:9b:49:bc

          inet addr:192.168.134.128  Bcast:192.168.134.255  Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fe9b:49bc/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:11545 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6177 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:923360 (923.3 KB)  TX bytes:1712607 (1.7 MB)

EXAMPLE-9:

To Change MTU for an Network Interface:

# ifconfig eth0 mtu 1000

output:
# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:0c:29:9b:49:bc

          inet addr:192.168.134.128  Bcast:192.168.134.255  Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fe9b:49bc/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1000  Metric:1
          RX packets:11545 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6177 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:923360 (923.3 KB)  TX bytes:1712607 (1.7 MB)

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