# ifconfig

## NAME



           ifconfig - configure a network interface
    


## SYNOPSIS



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


## 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,
           default), **inet6**(IPv6), **ax25**(AMPR Packet Radio), **ddp**(Appletalk
           Phase 2), **ipx**(Novell IPX) and **netrom**(AMPR Packet radio).  All
           numbers supplied as parts in IPv4 dotted decimal notation may be
           decimal, octal, or hexadecimal, as specified in the ISO C standard
           (that is, a leading 0x or 0X implies hexadecimal; otherwise, a
           leading '0' implies octal; otherwise, the number is interpreted as
           decimal). Use of hexadecimal and octal numbers is not RFC-
           compliant and therefore its use is discouraged.
    


## OPTIONS



           **-a** display all interfaces which are currently available, even
                  if 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 syntax like **eth0:0**
                  for the first alias of eth0. You can use them to assign
                  more addresses. 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; you can suppress this behavior when using an
                  alias interface by appending an **-** to the alias (e.g.
                  **eth0:0-**).  It is also suppressed when using the IPv4
                  0.0.0.0 address as the kernel will use this to implicitly
                  delete alias interfaces.
    
           **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.
    
           **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.
    
           **name** _newname_
                  Change the name of this interface to _newname_. The interface
                  must be shut down first.
    


## NOTES



           Since 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 iptables(8)
           command.
    
           Since net-tools 1.60-4 ifconfig is printing byte counters and
           human readable counters with IEC 60027-2 units. So 1 KiB are 2^10
           byte. Note, the numbers are truncated to one decimal (which can by
           quite a large error if you consider 0.1 PiB is 112.589.990.684.262
           bytes :)
    
           Interrupt problems with Ethernet device drivers fail with EAGAIN
           _(SIOCSIIFLAGS: Resource temporarily unavailable)_ it is most likely
           a interrupt conflict. See
           _http://www.scyld.com/expert/irq-conflict.html _ for more
           information.
    


## FILES



           _/proc/net/dev_
           _/proc/net/if_inet6_
    


## BUGS



           Ifconfig uses the ioctl access method to get the full address
           information, which limits hardware addresses to 8 bytes.  Because
           Infiniband hardware address has 20 bytes, only the first 8 bytes
           are displayed correctly.  Please use **ip link** command from **iproute2**
           package to display link layer informations including the hardware
           address.
    
           While appletalk DDP and IPX addresses will be displayed they
           cannot be altered by this command.
    


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