linux ifconfig

Linux and Unix ifconfig command

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About ifconfig
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About ifconfig

Configure a network interface.

Syntax

ifconfig [-v] [-a] [-s] [interface]

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

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 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.

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 all interfaces which are currently available, even if they are down.
-s	display a short list (like netstat -i).
-v	be more verbose for some 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 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.
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	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 10Mbps Ethernet), AUI (external transceiver) and so on. The special medium type of auto can be used to tell the driver to auto-sense the media. Again, not all drivers can do 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. 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 (modem links, ISDN) to prevent fast bulk transfers from disturbing interactive traffic like telnet too much.

Notes

Since Linux
kernel release 2.2 there are no explicit interface statistics for alias
interfaces anymore. The statistics printed for the original address are
shared with all alias addresses on the same device. If you want
per-address statistics you should add explicit accounting rules for the
address using the ipchains or iptables command.

Interrupt problems with Ethernet device drivers fail with EAGAIN (SIOCSIIFLAGS: Resource temporarily unavailable), it is most likely a interrupt conflict.

Files

/proc/net/socket
/proc/net/dev
/proc/net/if_inet6

Examples

ifconfig eth0

View the network settings on the first Ethernet adapter installed in the computer, eth0.

ifconfig -a

Display information on all network interfaces on the server, whether active or inactive.

ifconfig eth0 down

If eth0 exists, take it down, causing it to cease sending or receiving any information.

ifconfig eth0 up

If eth0 exists and is in the down state, bring it up, allowing it to to send and receive information.

ifconfig eth0 192.168.1.102 netmask 255.255.255.0 broadcast 192.168.1.255

Configure eth0 with the above values for IP, netmask and broadcast address.

Related commands

arp
dhclient
ifdown
ifup
ip
iwconfig
ping
netstat
route