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IFCONFIG(8)                      Linux System Administrator's Manual                     IFCONFIG(8)



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  ad‐
       dress 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 hexadeci‐
       mal,  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  in‐
              terfaces,  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  ad‐
              dress 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 net‐
              work 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 inter‐
              face.  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 di‐
              rect 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 opera‐
              tion.  The keyword must be followed by the name of the hardware class and  the  print‐
              able  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 kernel release 2.2 there are no explicit interface statistics for alias interfaces any‐
       more. 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.

       Interrupt problems with Ethernet device drivers fail with EAGAIN (SIOCSIIFLAGS: Resource tem‐
       porarily  unavailable)  it  is most likely a interrupt conflict. See http://www.scyld.com/ex‐
       pert/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 hard‐
       ware  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 com‐
       mand.

SEE ALSO
       route(8), netstat(8), arp(8), rarp(8), iptables(8), ifup(8), interfaces(5).
       http://physics.nist.gov/cuu/Units/binary.html - Prefixes for binary multiples

AUTHORS
       Fred N. van Kempen, <waltje AT uwalt.org>
       Alan Cox, <Alan.Cox AT linux.org>
       Phil Blundell, <Philip.Blundell AT pobox.com>
       Andi Kleen
       Bernd Eckenfels, <net-tools AT lina.de>



net-tools                                    2008-10-03                                  IFCONFIG(8)