IWCONFIG

Section: Linux Programmer's Manual (8)
Updated: 22 June 2004
 

NAME

iwconfig - configure a wireless network interface  

SYNOPSIS

iwconfig [interface]
iwconfig interface [essid X] [nwid N] [freq F] [channel C]
[sens S] [mode M] [ap A] [nick NN]
[rate R] [rts RT] [frag FT] [txpower T]
[enc E] [key K] [power P] [retry R]
[commit]
iwconfig --help
iwconfig --version  

DESCRIPTION

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.  

PARAMETERS

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).
Examples :
      iwconfig eth0 essid any
      iwconfig eth0 essid My Network
nwid/domain
Set the Network ID (in some products it may also be called Domain
ID). As all adjacent wireless networks share the same medium, this parameter is used to differenciate 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
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.
Examples :
      iwconfig eth0 freq 2422000000
      iwconfig eth0 freq 2.422G
      iwconfig eth0 channel 3
sens
Set the sensitivity threshold. This is the lowest signal level for
which the hardware attempt packet reception, signals weaker than this are ignored. This is used to avoid receiving background noise, so you should set it according to the average noise level. Positive values are assumed to be the raw value used by the hardware or a percentage, negative values are assumed to be dBm.
With some hardware, this parameter also controls the defer threshold (lowest signal level for which the hardware consider the channel busy) and the handover threshold (signal level where the hardware start looking for a new access point).
Example :
      iwconfig eth0 sens -80
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 acts as a passive monitor and only receives packets) or Auto.
Example :
      iwconfig eth0 mode Managed
      iwconfig eth0 mode Ad-Hoc
ap
Force the card to register to the Access Point given by the address,
if it is possible. 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
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 diagnostic tools may use it.
Example :
      iwconfig eth0 nickname My Linux Node
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 bit-rates lower and equal than this value.
Examples :
      iwconfig eth0 rate 11M
      iwconfig eth0 rate auto
      iwconfig eth0 rate 5.5M auto
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 disable 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 ; a value equal to the maximum packet size disable the mechanism. 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 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]
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'. 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 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 off
      iwconfig eth0 power min period 2 power max period 4
txpower
For cards supporting multiple transmit powers, set 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
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). The 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 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 min limit 8
commit
Some cards may not apply changes done through Wireless Extensions
immediately (they may wait to agregate 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.
 

DISPLAY

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 parameter you can set, please refer to the previous part for a detailed explanation of them.
Some parameters are only displayed in short/abreviated 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 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.

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/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.
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.
 

AUTHOR

Jean Tourrilhes - jt@hpl.hp.com  

FILES

/proc/net/wireless  

SEE ALSO

ifconfig(8), iwspy(8), iwlist(8), iwevent(8), iwpriv(8), wireless(7).


 

Index

NAME
SYNOPSIS
DESCRIPTION
PARAMETERS
DISPLAY
AUTHOR
FILES
SEE ALSO
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