1 Iwconfig

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 that 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 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 be called Domain ID). The ESSID is used to identify cells that are part of the same virtual network. As opposed to the NWID, which defines a single cell, the ESSID defines a group of cells connected via repeaters or infrastructure, where the user may roam. 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 is also called Domain 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. 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. Values below 1000 are the channel number, values over this are 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; signals 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 controls 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 synchronization 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.

Examples:

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 reenable 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.

Examples:

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 is completely an 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 bits lower than and equal to 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 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 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 splits an IP packet in a burst of smaller fragments transmitted on the medium. In most cases this adds overhead, but in very noisy environments this reduces the error penalty. This parameter sets the maximum fragment size. A value equal to the maximum packet size disables 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 sets the system in open mode (accept nonencrypted packets), and restricted discards nonencrypted 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 precedence.

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 in 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 Watts, 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 you to set the behavior of the retry mechanism. To set the maximum number of retries, enter limit 'value'. This is an absolute value (without unit). To set the maximum length of time the MAC should retry, enter lifetime 'value'. By default, this value is 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 aggregate the changes or apply them 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 that 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). (See preceding for explanations of what these parameters mean.)

If the label for bit-rate 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 transmitted).

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.

Author: Jean Tourrilhes (jt@hpl.hp.com)

Files: /proc/net/wireless

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