Ubuntu Manpage: ifconfig - configure a network interface

Provided by: net-tools_1.60+git20180626.aebd88e-1ubuntu1_amd64

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.

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.

       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.

AUTHORS

       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>