ifconfig(8) — Linux manual page


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

NAME         top

       ifconfig - configure a network interface

SYNOPSIS         top

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

DESCRIPTION         top

       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

Address Families         top

       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         top

       -a     display all interfaces which are currently available, even if

       -s     display a short list (like netstat -i)

       -v     be more verbose for some error conditions

              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 address as the
              kernel will use this to implicitly delete alias interfaces.

       down   This flag causes the driver for this interface to be shut

       [-]arp Enable or disable the use of the ARP protocol on this

              Enable or disable the promiscuous mode of the interface.  If
              selected, all packets on the network will be received by the

              Enable or disable all-multicast mode.  If selected, all
              multicast packets on the network will be received by the

       mtu N  This parameter sets the Maximum Transfer Unit (MTU) of an

       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

       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).

              Set the multicast flag on the interface. This should not
              normally be needed as the drivers set the flag correctly

              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

NOTES         top

       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         top


BUGS         top

       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

       While appletalk DDP and IPX addresses will be displayed they cannot
       be altered by this command.

SEE ALSO         top

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

AUTHORS         top

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

COLOPHON         top

       This page is part of the net-tools (networking utilities) project.
       Information about the project can be found at 
       ⟨http://net-tools.sourceforge.net/⟩.  If you have a bug report for
       this manual page, see ⟨http://net-tools.sourceforge.net/⟩.  This page
       was obtained from the project's upstream Git repository
       ⟨git://git.code.sf.net/p/net-tools/code⟩ on 2020-08-13.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2018-11-03.)  If you discover any rendering problems in
       this HTML version of the page, or you believe there is a better or
       more up-to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not part
       of the original manual page), send a mail to man-pages@man7.org

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

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