|
HTML rendering created 2026-01-16 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OUTPUT | NOTES | FILES | BUGS | SEE ALSO | AUTHORS | COLOPHON |
|
|
|
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 aftype 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.
-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 M This parameter sets the Maximum Transfer Unit (MTU) of an
interface to M bytes.
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 address to an interface.
del addr/prefixlen
Remove an address from an interface.
tunnel ::aa.bb.cc.dd
Create a new SIT (IPv6-in-IPv4) device, tunnelling to the
given destination.
irq I Set the interrupt line used by this device. Not all
devices can dynamically change their IRQ setting.
io_addr Mem
Set the start address in I/O space for this device. Only a
few old devices need this.
mem_start Mem
Set the start address for shared memory used by this
device. Only a few old 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 hwclass hwaddr
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 hwclass 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.
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.
address
The IP address to be assigned to this interface.
Interface Statistics Table (-s)
The table lists active (default) or all known (-a) kernel
interfaces. With the -s option it is the same output as netstat
-i.
> ifconfig -s enp2s0f0
Iface MTU RX-OK RX-ERR RX-DRP RX-OVR TX-OK TX-ERR TX-DRP TX-OVR Flg
enp2s0f0 1500 18668761 0 1318 0 26038367 0 0 0 BMRU
The result table shows the following columns:
Iface Name and alias prefix of the network interface.
MTU The maximum transfer unit in bytes of this interface.
RX-OK Number of successfully received packets since interface
statistic was reset.
RX-ERR Total count of receive errors since statistic reset. This
includes: rx_errors (general receive errors), rx_crc_errors
(packets received with a CRC checksum failure),
rx_frame_errors (frame alignment errors, corrupted).
RX-DRP Number of incoming packets that were dropped before
reaching the protocol stack. Common causes: no buffer
space in the driver, congestion, or resource limitations.
RX-OVR Number of packets dropped due to FIFO buffer overflows in
the NIC or driver. Common causes: the hardware could not
push frames fast enough to the system.
TX-OK Number of packets successfully transmitted since interface
statistic was reset.
TX-ERR Number of transmit errors. Includes collisions, carrier
loss, and other transmission failures.
TX-DRP Number of packets dropped by the driver before being sent
(e.g., due to congestion or lack of buffer space).
TX-OVR Number of packets lost due to transmit FIFO overflows in
the hardware.
Flg The flags for this interface, as listed below.
Interface Flags
The list of interface flags used in the short and detailed
interface output. The names of the bit flag constants of the
SIOCGIFFLAGS control are listed in netdevice(7).
A, ALLMULTI
Accepts all multicast packets (IFF_ALLMULTI).
B, BROADCAST
Interface supports broadcast communication (IFF_BROADCAST).
D, DEBUG
Internal debugging for the interface enabled (IFF_DEBUG).
L, LOOPBACK
Interface is a loopback device (IFF_LOOPBACK).
M, MULTICAST
Interface supports multicast communication (IFF_MULTICAST).
d, DYNAMIC
Address is dynamically set (e.g. by DHCP) (IFF_DYNAMIC).
P, PROMISC
Interface is in promiscuous mode (captures all packets)
(IFF_PROMISC). This flag might not reliably show promisc
mode.
N, NOTRAILERS
Avoid use of trailers in packets (IFF_NOTRAILERS).
O, NOARP
Interface does not use ARP (IFF_NOARP).
p, POINTOPOINT
Interface is point-to-point (has a peer instead of
broadcast) (IFF_POINTOPOINT).
s, SLAVE
Interface is part of a bonded device (IFF_SLAVE).
m, MASTER
Interface controls a bonded device (IFF_MASTER).
R, RUNNING
Interface is operational and resources are allocated
(IFF_RUNNING).
U, UP Interface is administratively up (IFF_UP).
[NO FLAGS], <>
If the bitmask for the interface status is 0.
Interface Details
Sample output for the details of a single interface:
> ifconfig enp2s0f0
enp2s0f0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 203.0.113.9 netmask 255.255.255.0 broadcast 203.0.113.255
inet6 fe80::a8bb:ccff:fedd:eeff prefixlen 64 scopeid 0x20<link>
inet6 2001:db8::a8bb:ccff:fedd:eeff prefixlen 64 scopeid 0x0<global>
ether aa:bb:cc:dd:ee:ff txqueuelen 1000 (Ethernet)
RX packets 18668507 bytes 9459465501 (8.8 GiB)
RX compressed 0
RX errors 0 dropped 1318 overruns 0 frame 0
TX packets 26038199 bytes 16983080620 (15.8 GiB)
TX compressed 0
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
device interrupt 30
The output of the interface list is the same as netstat -i -e.
For each interface there is a block starting with the interface
name the flags and the mtu, optional outfil and keepalive.
Then one line for each address, prefixed with the address type and
its type specifc details.
In the example is one IPv4 (inet) address. it specifies
netmask, optional broadcast. If the point-to-point flag is
set if will show destination address.
The example follows with two IPv6 (inet6) addresses. Such
a line specifies addresss, prefixlen, and scopeid:
compat IPv4 compatibility address.
global A Global Unicast Address (UGA).
site A site-unique address.
link A link-local address.
host A loopback address.
This is followed with a line for the hardware address family
(ether in this case). This line contains txqueuelen if available.
If the device is configured for port selection, it has a media
line.
After that the packets statistics for transmit (TX) and receive
(RX) are shown (same as in the short format above, but the
different error counters are shown seperate). Additionally the
total number of bytes (frame sizes total) are shown (with a human
friendly formatting as comment). The compressed packet counter
lines are optional.
The final device line lists optional driver details, with some of
the following keywords: interrupt, base, memory, and dma.
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.
/proc/net/dev /proc/net/if_inet6
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.
Homepage of the net-tools project:
⟨https://net-tools.sourceforge.io⟩
Prefixes for binary multiples (NIST):
⟨https://physics.nist.gov/cuu/Units/binary.html⟩
route(8), netstat(8), arp(8), ip-link(8), iptables(8)
interfaces(5), ip(7), netdevice(7)
Fred N. van Kempen <[email protected]>,
Alan Cox <[email protected]>, Andi Kleen,
Phil Blundell <[email protected]>,
Bernd Eckenfels <[email protected]>.
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 2026-01-16. (At that
time, the date of the most recent commit that was found in the
repository was 2025-12-12.) 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
[email protected]
net-tools 2025-09-10 IFCONFIG(8)
Pages that refer to this page: getifaddrs(3), if_nameindex(3), if_nametoindex(3), sk98lin(4), wavelan(4), proc(5), proc_pid_net(5), arp(8), nameif(8), netstat(8), plipconfig(8), rarp(8), route(8)
|
HTML rendering created 2026-01-16 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|