Linux manpage

manpage ifconfig

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


ifconfig – configure a network interface


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


       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 RaâАР
       dio), 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.


-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

              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  asâАР
              sign  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 down.

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

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

              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.

              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  transâАР
              ceiver) 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

       [-]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 lisâАР
              tening 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 themselves.

              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.


       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 adâАР
       dress 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 for more information.




       Ifconfig uses the ioctl access method to get the full address information, which limits hardware addresses to 8 bytes.  Because Infiniband  hardâАР
       ware  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.


       route(8), netstat(8), arp(8), rarp(8), iptables(8), ifup(8), interfaces(5). - Prefixes for binary multiples


       Fred N. van Kempen, <>
       Alan Cox, <>
       Phil Blundell, <>
       Andi Kleen
       Bernd Eckenfels, <>

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

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