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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.
essid 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"
nwid 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
nick[name]
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"
mode 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
freq/channel
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
- ap
- 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
rate/bit[rate]
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 bitrates
lower and equal than this value.
Examples :
iwconfig eth0 rate 11M
iwconfig eth0 rate auto
iwconfig eth0 rate 5.5M auto
txpower
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
sens 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
retry 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
in 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[_threshold]
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
frag[mentation_threshold]
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
key/enc[ryption]
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 nonencrypted
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]
power 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
modu[lation]
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
independantly, 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
commit 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).
Access Point/Cell
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 adhoc
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.
Link quality
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.
Signal level
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/wire_less
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.
Noise level
Background noise level (when no packet is transmitted). Similar
comments as for Signal level.
Rx invalid nwid
Number of packets received with a different NWID or ESSID. Used
to detect configuration problems or adjacent network existence
(on the same frequency).
Rx invalid crypt
Number of packets that the hardware was unable to decrypt. This
can be used to detect invalid encryption settings.
Rx invalid frag
Number of packets for which the hardware was not able to properly
re-assemble the link layer fragments (most likely one was
missing).
Tx excessive retries
Number of packets that the hardware failed to deliver. Most MAC
protocols will retry the packet a number of times before giving
up.
Invalid misc
Other packets lost in relation with specific wireless operations.
Missed beacon
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)
.
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