iwconfig - configure a wireless network interface
iwconfig [interface]
iwconfig interface [essid
X] [nwid N] [mode
M] [freq
F"]
[channel
C][sens S
][ap A
][nick"NN]
[rate R] [rts
RT] [frag FT]
[txpower T]
[enc E] [key
K] [power P] [retry
R]
[modu
M"][commit]
iwconfig --help
iwconfig --version
Iwconfig is similar to ifconfig(8), but is dedicated to the wireless interfaces. It is used to set the parameters of the network interface which are specific to the wireless operation (for example : the frequency). Iwconfig may also be used to display those parameters, and the wireless statistics (extracted from /proc/net/wireless).
All these parameters and statistics are device dependent. Each driver will provide only some of them depending on hardware support, and the range of values may change. Please refer to the man page of each device for details.
Set the ESSID (or Network Name - in some products it may also be
called Domain ID). The ESSID is used to identify cells which are part of
the same virtual network.
As opposed to the AP Address or NWID which define a single cell, the
ESSID defines a group of cells connected via repeaters or
infrastructure, where the user may roam transparently.
With some cards, you may disable the ESSID checking (ESSID promiscuous)
with off or any (and on to reenable
it).
If the ESSID of your network is one of the special keywords
(off, on or any), you should use --
to escape it.
Examples :
iwconfig eth0 essid any
" iwconfig eth0 essid My Network""
" iwconfig eth0 essid -- ANY""
Set the Network ID. As all adjacent wireless networks share the same
medium, this parameter is used to differentiate them (create logical
colocated networks) and identify nodes belonging to the same cell.
This parameter is only used for pre-802.11 hardware, the 802.11 protocol
uses the ESSID and AP Address for this function.
With some cards, you may disable the Network ID checking (NWID
promiscuous) with off (and on to reenable it).
Examples :
" iwconfig eth0 nwid AB34
iwconfig eth0 nwid off
Set the nickname, or the station name. Some 802.11 products do define
it, but this is not used as far as the protocols (MAC, IP, TCP) are
concerned and completely useless as far as configuration goes. Only some
wireless diagnostic tools may use it.
Example :
" iwconfig eth0 nickname My Linux Node""
Set the operating mode of the device, which depends on the network
topology. The mode can be Ad-Hoc (network composed of only one
cell and without Access Point), Managed (node connects to a
network composed of many Access Points, with roaming), Master
(the node is the synchronisation master or acts as an Access Point),
Repeater (the node forwards packets between other wireless
nodes), Secondary (the node acts as a backup master/repeater),
Monitor (the node is not associated with any cell and passively
monitor all packets on the frequency) or Auto.
Example :
iwconfig eth0 mode Managed
iwconfig eth0 mode Ad-Hoc
Set the operating frequency or channel in the device. A value below
1000 indicates a channel number, a value greater than 1000 is a
frequency in Hz. You may append the suffix k, M or G to the value (for
example, "2.46G" for 2.46 GHz frequency), or add enough '0'.
Channels are usually numbered starting at 1, and you may use
iwlist(8) to get the total number of channels, list the
available frequencies, and display the current frequency as a channel.
Depending on regulations, some frequencies/channels may not be
available.
When using Managed mode, most often the Access Point dictates the
channel and the driver may refuse the setting of the frequency. In
Ad-Hoc mode, the frequency setting may only be used at initial cell
creation, and may be ignored when joining an existing cell.
You may also use off or auto to let the card pick up
the best channel (when supported).
Examples :
iwconfig eth0 freq 2422000000
iwconfig eth0 freq 2.422G
iwconfig eth0 channel 3
iwconfig eth0 channel auto
Force the card to register to the Access Point given by the address,
if it is possible. This address is the cell identity of the Access
Point, as reported by wireless scanning, which may be different from its
network MAC address. If the wireless link is point to point, set the
address of the other end of the link. If the link is ad-hoc, set the
cell identity of the ad-hoc network.
When the quality of the connection goes too low, the driver may revert
back to automatic mode (the card selects the best Access Point in
range).
You may also use off to re-enable automatic mode without
changing the current Access Point, or you may use any or
auto to force the card to reassociate with the currently best
Access Point.
Example :
iwconfig eth0 ap 00:60:1D:01:23:45
iwconfig eth0 ap any
iwconfig eth0 ap off
For cards supporting multiple bit rates, set the bit-rate in b/s. The
bit-rate is the speed at which bits are transmitted over the medium, the
user speed of the link is lower due to medium sharing and various
overhead.
You may append the suffix k, M or G to the value (decimal multiplier :
10^3, 10^6 and 10^9 b/s), or add enough '0'. Values below 1000 are card
specific, usually an index in the bit-rate list. Use auto to
select automatic bit-rate mode (fallback to lower rate on noisy
channels), which is the default for most cards, and fixed to
revert back to fixed setting. If you specify a bit-rate value and append
auto, the driver will use all bit-rates lower and equal than
this value.
Examples :
iwconfig eth0 rate 11M
iwconfig eth0 rate auto
iwconfig eth0 rate 5.5M auto
For cards supporting multiple transmit powers, sets the transmit
power in dBm. If W is the power in Watt, the power in dBm is
P = 30 + 10.log(W). If the value is postfixed by mW,
it will be automatically converted to dBm.
In addition, on and off enable and disable the radio,
and auto and fixed enable and disable power control
(if those features are available).
Examples :
iwconfig eth0 txpower 15
iwconfig eth0 txpower 30mW
iwconfig eth0 txpower auto
iwconfig eth0 txpower off
Set the sensitivity threshold. This define how sensitive is the card
to poor operating conditions (low signal, interference). Positive values
are assumed to be the raw value used by the hardware or a percentage,
negative values are assumed to be dBm. Depending on the hardware
implementation, this parameter may control various functions.
On modern cards, this parameter usually control handover/roaming
threshold, the lowest signal level for which the hardware remains
associated with the current Access Point. When the signal level goes
below this threshold the card starts looking for a new/better Access
Point. Some cards may use the number of missed beacons to trigger this.
For high density of Access Points, a higher threshold make sure the card
is always associated with the best AP, for low density of APs, a lower
threshold minimise the number of failed handoffs.
On more ancient card this parameter usually controls the defer
threshold, the lowest signal level for which the hardware considers the
channel busy. Signal levels above this threshold make the hardware
inhibits its own transmission whereas signals weaker than this are
ignored and the hardware is free to transmit. This is usually strongly
linked to the receive threshold, the lowest signal level for which the
hardware attempts packet reception. Proper setting of these thresholds
prevent the card to waste time on background noise while still receiving
weak transmissions. Modern designs seems to control those thresholds
automatically.
Example :
iwconfig eth0 sens -80
iwconfig eth0 sens 2
Most cards have MAC retransmissions, and some allow to set the
behaviour of the retry mechanism.
To set the maximum number of retries, enter limit `value'. This
is an absolute value (without unit), and the default (when nothing is
specified). To set the maximum length of time the MAC should retry,
enter lifetime `value'. By defaults, this value is in seconds,
append the suffix m or u to specify values in milliseconds or
microseconds.
You can also add the short, long, min and
max modifiers. If the card supports automatic mode, they define
the bounds of the limit or lifetime. Some other cards define different
values depending on packet size, for example in 802.11 min
limit is the short retry limit (non RTS/CTS packets).
Examples :
iwconfig eth0 retry 16
iwconfig eth0 retry lifetime 300m
iwconfig eth0 retry short 12
iwconfig eth0 retry min limit 8
RTS/CTS adds a handshake before each packet transmission to make sure
that the channel is clear. This adds overhead, but increases performance
in case of hidden nodes or a large number of active nodes. This
parameter sets the size of the smallest packet for which the node sends
RTS ; a value equal to the maximum packet size disables the mechanism.
You may also set this parameter to auto, fixed or
off.
Examples :
iwconfig eth0 rts 250
iwconfig eth0 rts off
Fragmentation allows to split an IP packet in a burst of smaller
fragments transmitted on the medium. In most cases this adds overhead,
but in a very noisy environment this reduces the error penalty and allow
packets to get through interference bursts. This parameter sets the
maximum fragment size which is always lower than the maximum packet
size.
This parameter may also control Frame Bursting available on some cards,
the ability to send multiple IP packets together. This mechanism would
be enabled if the fragment size is larger than the maximum packet
size.
You may also set this parameter to auto, fixed or
off.
Examples :
iwconfig eth0 frag 512
iwconfig eth0 frag off
Used to manipulate encryption or scrambling keys and security
mode.
To set the current encryption key, just enter the key in hex digits as
XXXX-XXXX-XXXX-XXXX or XXXXXXXX. To set a key other
than the current key, prepend or append [index] to the key
itself (this won't change which is the active key). You can also enter
the key as an ASCII string by using the s: prefix. Passphrase
is currently not supported.
To change which key is the currently active key, just enter
[index] (without entering any key value).
off and on disable and reenable encryption.
The security mode may be open or restricted, and its
meaning depends on the card used. With most cards, in open mode
no authentication is used and the card may also accept non-encrypted
sessions, whereas in restricted mode only encrypted sessions
are accepted and the card will use authentication if available.
If you need to set multiple keys, or set a key and change the active
key, you need to use multiple key directives. Arguments
can be put in any order, the last one will take precedence.
Examples :
iwconfig eth0 key 0123-4567-89
iwconfig eth0 key [3] 0123-4567-89
iwconfig eth0 key s:password [2]
iwconfig eth0 key [2]
iwconfig eth0 key open
iwconfig eth0 key off
iwconfig eth0 key restricted [3] 0123456789
iwconfig eth0 key 01-23 key 45-67 [4] key [4]
Used to manipulate power management scheme parameters and mode.
To set the period between wake ups, enter period `value'. To
set the timeout before going back to sleep, enter timeout
`value'. To set the generic level of power saving, enter saving
`value'. You can also add the min and max
modifiers. By default, those values are in seconds, append the suffix m
or u to specify values in milliseconds or microseconds. Sometimes, those
values are without units (number of beacon periods, dwell, percentage or
similar).
off and on disable and reenable power management.
Finally, you may set the power management mode to all (receive
all packets), unicast (receive unicast packets only, discard
multicast and broadcast) and multicast (receive multicast and
broadcast only, discard unicast packets).
Examples :
iwconfig eth0 power period 2
iwconfig eth0 power 500m unicast
iwconfig eth0 power timeout 300u all
iwconfig eth0 power saving 3
iwconfig eth0 power off
iwconfig eth0 power min period 2 power max period 4
Force the card to use a specific set of modulations. Modern cards
support various modulations, some which are standard, such as 802.11b or
802.11g, and some proprietary. This command force the card to only use
the specific set of modulations listed on the command line. This can be
used to fix interoperability issues.
The list of available modulations depend on the card/driver and can be
displayed using iwlist modulation. Note that some card/driver
may not be able to select each modulation listed independently, some may
come as a group. You may also set this parameter to auto let
the card/driver do its best.
Examples :
iwconfig eth0 modu 11g
iwconfig eth0 modu CCK OFDMa
iwconfig eth0 modu auto
Some cards may not apply changes done through Wireless Extensions
immediately (they may wait to aggregate the changes or apply it only
when the card is brought up via ifconfig). This command (when
available) forces the card to apply all pending changes.
This is normally not needed, because the card will eventually apply the
changes, but can be useful for debugging.
For each device which supports wireless extensions, iwconfig will display the name of the MAC protocol used (name of device for proprietary protocols), the ESSID (Network Name), the NWID, the frequency (or channel), the sensitivity, the mode of operation, the Access Point address, the bit-rate, the RTS threshold, the fragmentation threshold, the encryption key and the power management settings (depending on availability).
The parameters displayed have the same meaning and values as the
parameters you can set, please refer to the previous part for a detailed
explanation of them.
Some parameters are only displayed in short/abbreviated form (such as
encryption). You may use iwlist(8) to get all the
details.
Some parameters have two modes (such as bitrate). If the value is
prefixed by `=', it means that the parameter is fixed
and forced to that value, if it is prefixed by `:', the
parameter is in automatic mode and the current value is shown (and may
change).
An address equal to 00:00:00:00:00:00 means that the card failed to associate with an Access Point (most likely a configuration issue). The Access Point parameter will be shown as Cell in ad-hoc mode (for obvious reasons), but otherwise works the same.
If /proc/net/wireless exists, iwconfig will also display its content. Note that those values will depend on the driver and the hardware specifics, so you need to refer to your driver documentation for proper interpretation of those values.
Overall quality of the link. May be based on the level of contention or interference, the bit or frame error rate, how good the received signal is, some timing synchronisation, or other hardware metric. This is an aggregate value, and depends totally on the driver and hardware.
Received signal strength (RSSI - how strong the received signal is). May be arbitrary units or dBm, iwconfig uses driver meta information to interpret the raw value given by /proc/net/wireless and display the proper unit or maximum value (using 8 bit arithmetic). In Ad-Hoc mode, this may be undefined and you should use iwspy.
Background noise level (when no packet is transmitted). Similar comments as for Signal level.
Number of packets received with a different NWID or ESSID. Used to detect configuration problems or adjacent network existence (on the same frequency).
Number of packets that the hardware was unable to decrypt. This can be used to detect invalid encryption settings.
Number of packets for which the hardware was not able to properly re-assemble the link layer fragments (most likely one was missing).
Number of packets that the hardware failed to deliver. Most MAC protocols will retry the packet a number of times before giving up.
Other packets lost in relation with specific wireless operations.
Number of periodic beacons from the Cell or the Access Point we have missed. Beacons are sent at regular intervals to maintain the cell coordination, failure to receive them usually indicates that the card is out of range.
Jean Tourrilhes - jt@hpl.hp.com
/proc/net/wireless
ifconfig(8), iwspy(8), iwlist(8), iwevent(8), iwpriv(8), wireless(7).