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).
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/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
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 bit-rates 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).
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
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
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
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
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.
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
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 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.
