1. Computing
Linux / Unix Command: iwconfig
Command Library

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 dependant. Each driver will provide only some of them depending on the hardware support, and the range of value 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 called Domain ID). The ESSID is used to identify cells which are part of the same virtual network.
As opposed to the NWID which defines a single cell, the ESSID defines a group of cell connected via repeaters or infrastructure, where the user may roam. With some card, 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 is also 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 belonguing to the same cell. With some card, 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. Value below 1000
are the channel number, value over this is the frequency in Hz. You must 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 iwpriv(8) to get the total number of channels and list the available frequencies. Depending on regulations, some frequencies/channels may not be available.
Examples :
iwconfig eth0 freq 2.422G
iwconfig eth0 channel 3
sens
Set the sensitivity threshold. This is the lowest signal level for
which we attempt a packet reception, signal lower than this are not received. 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 control the defer threshold (lowest signal level for which we consider the channel busy) and the handover threshold (lowest signal level where we stay associated with the current 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 act as an Access Point), Repeater (the node forward packets between other wireless nodes), Secondary (the node act as a backup master/repeater), Monitor (the node act 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 finds 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 current 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. Most 802.11 products do define
it, but this is not used as far as the protocols (MAC, IP, TCP) are concerned and completely accessory as far as configuration goes. In fact 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 overhead.
You must 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 the 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 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 increase performance in case of hidden nodes or large number of active nodes. This parameters set the size of the smallest packet for which the node sends RTS, a value equal to the maximum packet size disable the scheme. You may also set this parameter to auto, fixed or off.
Examples :
iwconfig eth0 rts 250
iwconfig eth0 rts off
frag[mentation_threshold]
Fragmentation allow to split a IP packet in a burst of smaller
fragments transmitted on the medium. In most cases this adds overhead, but in very noisy environment this reduce the error penalty. This parameter set the maximum fragment size, a value equal to the maximum packet size disable the scheme. 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 encryption 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 current active key, just enter [index] (without entering any key value).
off and on disable and reenable encryption, open set the system in open mode (accept non-encrypted packets) and restricted discard non-encrypted packets.
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 precendence.
Examples :
iwconfig eth0 key 0123-4567-89
iwconfig eth0 key s:password [2]
iwconfig eth0 key [2] 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 up, 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 defaults, those values are in seconds, append the suffix m or u to specify values un milliseconds or microseconds. Sometimes, those values are without units (number of dwell or the like).
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 un milliseconds or microseconds.
You can also add the min and max modifiers. If the card support 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) force the card to apply all pending changes.
This is normally not needed, because the card will eventually apply the changes, but can be usefull for debugging.

DISPLAY

For each device which support 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).
See above for explanations of what these parameters mean.
If the label for bitrate is followed by `=', it means that the parameter is fixed and forced to that value, if it is followed by `:' it is only the current value (device in normal auto mode).

If /proc/net/wireless exists, iwconfig will also display its content :

Link quality
Quality of the link or the modulation (what is the level of contention or interference, or how good the received signal is).
Signal level
Received signal strength (how strong the received signal is).
Noise level
Background noise level (when no packet is transmited).
invalid nwid
Number of packets received with a different NWID. Used to detect configuration problems or adjacent network existence.
invalid crypt
Number of packets that the hardware was unable to decrypt.
invalid misc
Other packets lost in relation with specific wireless operations.

SEE ALSO

ifconfig(8), iwspy(8), iwlist(8), iwpriv(8), wavelan(4), wavelan_cs(4), wvlan_cs(4), netwave_cs(4).


Important: Use the man command (% man) to see how a command is used on your particular computer.

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