Most wireless networks are based on the IEEE® 802.11 standards. A basic wireless network consists of multiple stations communicating with radios that broadcast in either the 2.4GHz or 5GHz band, though this varies according to the locale and is also changing to enable communication in the 2.3GHz and 4.9GHz ranges.
802.11 networks are organized in two ways. In infrastructure mode, one station acts as a master with all the other stations associating to it, the network is known as a BSS, and the master station is termed an access point (AP). In a BSS, all communication passes through the AP; even when one station wants to communicate with another wireless station, messages must go through the AP. In the second form of network, there is no master and stations communicate directly. This form of network is termed an IBSS and is commonly known as an ad-hoc network.
802.11 networks were first deployed in the 2.4GHz band using protocols defined by the IEEE® 802.11 and 802.11b standard. These specifications include the operating frequencies and the MAC layer characteristics, including framing and transmission rates, as communication can occur at various rates. Later, the 802.11a standard defined operation in the 5GHz band, including different signaling mechanisms and higher transmission rates. Still later, the 802.11g standard defined the use of 802.11a signaling and transmission mechanisms in the 2.4GHz band in such a way as to be backwards compatible with 802.11b networks.
Separate from the underlying transmission techniques, 802.11 networks have a variety of security mechanisms. The original 802.11 specifications defined a simple security protocol called WEP. This protocol uses a fixed pre-shared key and the RC4 cryptographic cipher to encode data transmitted on a network. Stations must all agree on the fixed key in order to communicate. This scheme was shown to be easily broken and is now rarely used except to discourage transient users from joining networks. Current security practice is given by the IEEE® 802.11i specification that defines new cryptographic ciphers and an additional protocol to authenticate stations to an access point and exchange keys for data communication. Cryptographic keys are periodically refreshed and there are mechanisms for detecting and countering intrusion attempts. Another security protocol specification commonly used in wireless networks is termed WPA, which was a precursor to 802.11i. WPA specifies a subset of the requirements found in 802.11i and is designed for implementation on legacy hardware. Specifically, WPA requires only the TKIP cipher that is derived from the original WEP cipher. 802.11i permits use of TKIP but also requires support for a stronger cipher, AES-CCM, for encrypting data. The AES cipher was not required in WPA because it was deemed too computationally costly to be implemented on legacy hardware.
The other standard to be aware of is 802.11e. It defines protocols for deploying multimedia applications, such as streaming video and voice over IP (VoIP), in an 802.11 network. Like 802.11i, 802.11e also has a precursor specification termed WME (later renamed WMM) that has been defined by an industry group as a subset of 802.11e that can be deployed now to enable multimedia applications while waiting for the final ratification of 802.11e. The most important thing to know about 802.11e and WME/WMM is that it enables prioritized traffic over a wireless network through Quality of Service (QoS) protocols and enhanced media access protocols. Proper implementation of these protocols enables high speed bursting of data and prioritized traffic flow.
FreeBSD supports networks that operate using 802.11a, 802.11b, and 802.11g. The WPA and 802.11i security protocols are likewise supported (in conjunction with any of 11a, 11b, and 11g) and QoS and traffic prioritization required by the WME/WMM protocols are supported for a limited set of wireless devices.
To use wireless networking, a wireless networking card is needed and the kernel needs to be configured with the appropriate wireless networking support. The kernel is separated into multiple modules so that only the required support needs to be configured.
The most
commonly used wireless devices are those that use parts made
by Atheros. These devices are supported by ath(4)
and require the following line to be added to
/boot/loader.conf
:
The Atheros driver is split up into three separate pieces: the driver (ath(4)), the hardware support layer that handles chip-specific functions (ath_hal(4)), and an algorithm for selecting the rate for transmitting frames. When this support is loaded as kernel modules, any dependencies are automatically handled. To load support for a different type of wireless device, specify the module for that device. This example is for devices based on the Intersil Prism parts (wi(4)) driver:
The examples in this section use an ath(4) device and the device name in the examples must be changed according to the configuration. A list of available wireless drivers and supported adapters can be found in the FreeBSD Hardware Notes, available on the Release Information page of the FreeBSD website. If a native FreeBSD driver for the wireless device does not exist, it may be possible to use the Windows® driver with the help of the NDIS driver wrapper.
In addition, the modules that implement cryptographic
support for the security protocols to use must be loaded.
These are intended to be dynamically loaded on demand by
the wlan(4) module, but for now they must be manually
configured. The following modules are available:
wlan_wep(4), wlan_ccmp(4), and wlan_tkip(4).
The wlan_ccmp(4) and wlan_tkip(4) drivers are
only needed when using the WPA or
802.11i security protocols. If the network does not use
encryption, wlan_wep(4) support is not needed. To
load these modules at boot time, add the following lines to
/boot/loader.conf
:
Once this information has been added to
/boot/loader.conf
, reboot the FreeBSD
box. Alternately, load the modules by hand using
kldload(8).
For users who do not want to use modules, it is possible to compile these drivers into the kernel by adding the following lines to a custom kernel configuration file:
With this information in the kernel configuration file, recompile the kernel and reboot the FreeBSD machine.
Information about the wireless device should appear in the boot messages, like this:
Infrastructure (BSS) mode is the mode that is typically used. In this mode, a number of wireless access points are connected to a wired network. Each wireless network has its own name, called the SSID. Wireless clients connect to the wireless access points.
To scan for available networks, use ifconfig(8). This request may take a few moments to complete as it requires the system to switch to each available wireless frequency and probe for available access points. Only the superuser can initiate a scan:
#
ifconfig wlan0
create wlandev ath0
#
ifconfig wlan0
up scan
SSID/MESH ID BSSID CHAN RATE S:N INT CAPS
dlinkap 00:13:46:49:41:76 11 54M -90:96 100 EPS WPA WME
freebsdap 00:11:95:c3:0d:ac 1 54M -83:96 100 EPS WPAThe interface must be up
before
it can scan. Subsequent scan requests do not require
the interface to be marked as up again.
The output of a scan request lists each
BSS/IBSS network
found. Besides listing the name of the network, the
SSID
, the output also shows the
BSSID
, which is the
MAC address of the access point. The
CAPS
field identifies the type of
each network and the capabilities of the stations
operating there:
Capability Code | Meaning |
---|---|
E | Extended Service Set (ESS). Indicates that the station is part of an infrastructure network rather than an IBSS/ad-hoc network. |
I | IBSS/ad-hoc network. Indicates that the station is part of an ad-hoc network rather than an ESS network. |
P | Privacy. Encryption is required for all data frames exchanged within the BSS using cryptographic means such as WEP, TKIP or AES-CCMP. |
S | Short Preamble. Indicates that the network is using short preambles, defined in 802.11b High Rate/DSSS PHY, and utilizes a 56 bit sync field rather than the 128 bit field used in long preamble mode. |
s | Short slot time. Indicates that the 802.11g network is using a short slot time because there are no legacy (802.11b) stations present. |
One can also display the current list of known networks with:
#
ifconfig wlan0
list scan
This information may be updated automatically by the
adapter or manually with a scan
request.
Old data is automatically removed from the cache, so over
time this list may shrink unless more scans are
done.
This section provides a simple example of how to make the wireless network adapter work in FreeBSD without encryption. Once familiar with these concepts, it is strongly recommend to use WPA to set up the wireless network.
There are three basic steps to configure a wireless network: select an access point, authenticate the station, and configure an IP address. The following sections discuss each step.
Most of the time, it is sufficient to let the system
choose an access point using the builtin heuristics.
This is the default behaviour when an interface is
marked as up or it is listed in
/etc/rc.conf
:
If there are multiple access points, a specific one can be selected by its SSID:
your_ssid_here
DHCP"In an environment where there are multiple access points with the same SSID, which is often done to simplify roaming, it may be necessary to associate to one specific device. In this case, the BSSID of the access point can be specified, with or without the SSID:
your_ssid_here
bssid xx:xx:xx:xx:xx:xx
DHCP"There are other ways to constrain the choice of an
access point, such as limiting the set of frequencies
the system will scan on. This may be useful for a
multi-band wireless card as scanning all the possible
channels can be time-consuming. To limit operation to a
specific band, use the mode
parameter:
11g
ssid your_ssid_here
DHCP"This example will force the card to operate in
802.11g, which is defined only for 2.4GHz frequencies
so any 5GHz channels will not be considered. This can
also be achieved with the
channel
parameter, which locks
operation to one specific frequency, and the
chanlist
parameter, to specify a list
of channels for scanning. More information about these
parameters can be found in ifconfig(8).
Once an access point is selected, the station needs to authenticate before it can pass data. Authentication can happen in several ways. The most common scheme, open authentication, allows any station to join the network and communicate. This is the authentication to use for test purposes the first time a wireless network is setup. Other schemes require cryptographic handshakes to be completed before data traffic can flow, either using pre-shared keys or secrets, or more complex schemes that involve backend services such as RADIUS. Open authentication is the default setting. The next most common setup is WPA-PSK, also known as WPA Personal, which is described in Section 31.3.3.1.3.1, “WPA-PSK”.
If using an Apple® AirPort® Extreme base
station for an access point, shared-key authentication
together with a WEP key needs to
be configured. This can be configured in
/etc/rc.conf
or by using
wpa_supplicant(8). For a single AirPort® base
station, access can be configured with:
1
wepkey 01234567
DHCP"In general, shared key authentication should be
avoided because it uses the WEP key
material in a highly-constrained manner, making it
even easier to crack the key. If
WEP must be used for compatibility
with legacy devices, it is better to use
WEP with open
authentication. More information regarding
WEP can be found in Section 31.3.3.1.4, “WEP”.
Once an access point is selected and the
authentication parameters are set, an
IP address must be obtained in
order to communicate. Most of the time, the
IP address is obtained via
DHCP. To achieve that, edit
/etc/rc.conf
and add
DHCP
to the configuration for the
device:
The wireless interface is now ready to bring up:
#
service netif start
Once the interface is running, use ifconfig(8)
to see the status of the interface
ath0
:
#
ifconfig wlan0
wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
ether 00:11:95:d5:43:62
inet 192.168.1.100 netmask 0xffffff00 broadcast 192.168.1.255
media: IEEE 802.11 Wireless Ethernet OFDM/54Mbps mode 11g
status: associated
ssid dlinkap channel 11 (2462 Mhz 11g) bssid 00:13:46:49:41:76
country US ecm authmode OPEN privacy OFF txpower 21.5 bmiss 7
scanvalid 60 bgscan bgscanintvl 300 bgscanidle 250 roam:rssi 7
roam:rate 5 protmode CTS wme burstThe status: associated
line means
that it is connected to the wireless network. The
bssid 00:13:46:49:41:76
is the
MAC address of the access point and
authmode OPEN
indicates that the
communication is not encrypted.
In an IP address cannot be
obtained from a DHCP server, set a
fixed IP address. Replace the
DHCP
keyword shown above with the
address information. Be sure to retain any other
parameters for selecting the access point:
192.168.1.100
netmask 255.255.255.0
ssid your_ssid_here
"Wi-Fi Protected Access (WPA) is a security protocol used together with 802.11 networks to address the lack of proper authentication and the weakness of WEP. WPA leverages the 802.1X authentication protocol and uses one of several ciphers instead of WEP for data integrity. The only cipher required by WPA is the Temporary Key Integrity Protocol (TKIP). TKIP is a cipher that extends the basic RC4 cipher used by WEP by adding integrity checking, tamper detection, and measures for responding to detected intrusions. TKIP is designed to work on legacy hardware with only software modification. It represents a compromise that improves security but is still not entirely immune to attack. WPA also specifies the AES-CCMP cipher as an alternative to TKIP, and that is preferred when possible. For this specification, the term WPA2 or RSN is commonly used.
WPA defines authentication and encryption protocols. Authentication is most commonly done using one of two techniques: by 802.1X and a backend authentication service such as RADIUS, or by a minimal handshake between the station and the access point using a pre-shared secret. The former is commonly termed WPA Enterprise and the latter is known as WPA Personal. Since most people will not set up a RADIUS backend server for their wireless network, WPA-PSK is by far the most commonly encountered configuration for WPA.
The control of the wireless connection and the key
negotiation or authentication with a server is done using
wpa_supplicant(8). This program requires a
configuration file,
/etc/wpa_supplicant.conf
, to run.
More information regarding this file can be found in
wpa_supplicant.conf(5).
WPA-PSK, also known as WPA Personal, is based on a pre-shared key (PSK) which is generated from a given password and used as the master key in the wireless network. This means every wireless user will share the same key. WPA-PSK is intended for small networks where the use of an authentication server is not possible or desired.
Always use strong passwords that are sufficiently long and made from a rich alphabet so that they will not be easily guessed or attacked.
The first step is the configuration of
/etc/wpa_supplicant.conf
with
the SSID and the pre-shared key of
the network:
Then, in /etc/rc.conf
,
indicate that the wireless device configuration will be
done with WPA and the
IP address will be obtained with
DHCP:
Then, bring up the interface:
#
service netif start
Starting wpa_supplicant.
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 5
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 6
DHCPOFFER from 192.168.0.1
DHCPREQUEST on wlan0 to 255.255.255.255 port 67
DHCPACK from 192.168.0.1
bound to 192.168.0.254 -- renewal in 300 seconds.
wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
ether 00:11:95:d5:43:62
inet 192.168.0.254 netmask 0xffffff00 broadcast 192.168.0.255
media: IEEE 802.11 Wireless Ethernet OFDM/36Mbps mode 11g
status: associated
ssid freebsdap channel 1 (2412 Mhz 11g) bssid 00:11:95:c3:0d:ac
country US ecm authmode WPA2/802.11i privacy ON deftxkey UNDEF
AES-CCM 3:128-bit txpower 21.5 bmiss 7 scanvalid 450 bgscan
bgscanintvl 300 bgscanidle 250 roam:rssi 7 roam:rate 5 protmode CTS
wme burst roaming MANUALOr, try to configure the interface manually using
the information in
/etc/wpa_supplicant.conf
:
#
wpa_supplicant -i wlan0
-c /etc/wpa_supplicant.conf
Trying to associate with 00:11:95:c3:0d:ac (SSID='freebsdap' freq=2412 MHz)
Associated with 00:11:95:c3:0d:ac
WPA: Key negotiation completed with 00:11:95:c3:0d:ac [PTK=CCMP GTK=CCMP]
CTRL-EVENT-CONNECTED - Connection to 00:11:95:c3:0d:ac completed (auth) [id=0 id_str=]The next operation is to launch dhclient(8) to get the IP address from the DHCP server:
#
dhclient wlan0
DHCPREQUEST on wlan0 to 255.255.255.255 port 67
DHCPACK from 192.168.0.1
bound to 192.168.0.254 -- renewal in 300 seconds.
#
ifconfig wlan0
wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
ether 00:11:95:d5:43:62
inet 192.168.0.254 netmask 0xffffff00 broadcast 192.168.0.255
media: IEEE 802.11 Wireless Ethernet OFDM/36Mbps mode 11g
status: associated
ssid freebsdap channel 1 (2412 Mhz 11g) bssid 00:11:95:c3:0d:ac
country US ecm authmode WPA2/802.11i privacy ON deftxkey UNDEF
AES-CCM 3:128-bit txpower 21.5 bmiss 7 scanvalid 450 bgscan
bgscanintvl 300 bgscanidle 250 roam:rssi 7 roam:rate 5 protmode CTS
wme burst roaming MANUALIf /etc/rc.conf
has an
ifconfig_wlan0="DHCP"
entry,
dhclient(8) will be launched automatically after
wpa_supplicant(8) associates with the access
point.
If DHCP is not possible or desired, set a static IP address after wpa_supplicant(8) has authenticated the station:
#
ifconfig wlan0
inet 192.168.0.100
netmask 255.255.255.0
#
ifconfig wlan0
wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
ether 00:11:95:d5:43:62
inet 192.168.0.100 netmask 0xffffff00 broadcast 192.168.0.255
media: IEEE 802.11 Wireless Ethernet OFDM/36Mbps mode 11g
status: associated
ssid freebsdap channel 1 (2412 Mhz 11g) bssid 00:11:95:c3:0d:ac
country US ecm authmode WPA2/802.11i privacy ON deftxkey UNDEF
AES-CCM 3:128-bit txpower 21.5 bmiss 7 scanvalid 450 bgscan
bgscanintvl 300 bgscanidle 250 roam:rssi 7 roam:rate 5 protmode CTS
wme burst roaming MANUALWhen DHCP is not used, the default gateway and the nameserver also have to be manually set:
#
route add default your_default_router
#
echo "nameserver your_DNS_server
" >> /etc/resolv.conf
The second way to use WPA is with an 802.1X backend authentication server. In this case, WPA is called WPA Enterprise to differentiate it from the less secure WPA Personal. Authentication in WPA Enterprise is based on the Extensible Authentication Protocol (EAP).
EAP does not come with an encryption method. Instead, EAP is embedded inside an encrypted tunnel. There are many EAP authentication methods, but EAP-TLS, EAP-TTLS, and EAP-PEAP are the most common.
EAP with Transport Layer Security (EAP-TLS) is a well-supported wireless authentication protocol since it was the first EAP method to be certified by the Wi-Fi alliance. EAP-TLS requires three certificates to run: the certificate of the Certificate Authority (CA) installed on all machines, the server certificate for the authentication server, and one client certificate for each wireless client. In this EAP method, both the authentication server and wireless client authenticate each other by presenting their respective certificates, and then verify that these certificates were signed by the organization's CA.
As previously, the configuration is done via
/etc/wpa_supplicant.conf
:
This field indicates the network name (SSID). | |
This example uses the RSN IEEE® 802.11i protocol, also known as WPA2. | |
The | |
This field indicates the EAP method for the connection. | |
The | |
The | |
The | |
The | |
The |
Then, add the following lines to
/etc/rc.conf
:
The next step is to bring up the interface:
#
service netif start
Starting wpa_supplicant.
DHCPREQUEST on wlan0 to 255.255.255.255 port 67 interval 7
DHCPREQUEST on wlan0 to 255.255.255.255 port 67 interval 15
DHCPACK from 192.168.0.20
bound to 192.168.0.254 -- renewal in 300 seconds.
wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
ether 00:11:95:d5:43:62
inet 192.168.0.254 netmask 0xffffff00 broadcast 192.168.0.255
media: IEEE 802.11 Wireless Ethernet DS/11Mbps mode 11g
status: associated
ssid freebsdap channel 1 (2412 Mhz 11g) bssid 00:11:95:c3:0d:ac
country US ecm authmode WPA2/802.11i privacy ON deftxkey UNDEF
AES-CCM 3:128-bit txpower 21.5 bmiss 7 scanvalid 450 bgscan
bgscanintvl 300 bgscanidle 250 roam:rssi 7 roam:rate 5 protmode CTS
wme burst roaming MANUALIt is also possible to bring up the interface manually using wpa_supplicant(8) and ifconfig(8).
With EAP-TTLS, both the authentication server and the client need a certificate. With EAP-TTLS, a client certificate is optional. This method is similar to a web server which creates a secure SSL tunnel even if visitors do not have client-side certificates. EAP-TTLS uses an encrypted TLS tunnel for safe transport of the authentication data.
The required configuration can be added to
/etc/wpa_supplicant.conf
:
This field specifies the EAP method for the connection. | |
The | |
The | |
The | |
This field specifies the authentication method used in the encrypted TLS tunnel. In this example, EAP with MD5-Challenge is used. The “inner authentication” phase is often called “phase2”. |
Next, add the following lines to
/etc/rc.conf
:
The next step is to bring up the interface:
#
service netif start
Starting wpa_supplicant.
DHCPREQUEST on wlan0 to 255.255.255.255 port 67 interval 7
DHCPREQUEST on wlan0 to 255.255.255.255 port 67 interval 15
DHCPREQUEST on wlan0 to 255.255.255.255 port 67 interval 21
DHCPACK from 192.168.0.20
bound to 192.168.0.254 -- renewal in 300 seconds.
wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
ether 00:11:95:d5:43:62
inet 192.168.0.254 netmask 0xffffff00 broadcast 192.168.0.255
media: IEEE 802.11 Wireless Ethernet DS/11Mbps mode 11g
status: associated
ssid freebsdap channel 1 (2412 Mhz 11g) bssid 00:11:95:c3:0d:ac
country US ecm authmode WPA2/802.11i privacy ON deftxkey UNDEF
AES-CCM 3:128-bit txpower 21.5 bmiss 7 scanvalid 450 bgscan
bgscanintvl 300 bgscanidle 250 roam:rssi 7 roam:rate 5 protmode CTS
wme burst roaming MANUALPEAPv0/EAP-MSCHAPv2 is the most common PEAP method. In this chapter, the term PEAP is used to refer to that method.
Protected EAP (PEAP) is designed as an alternative to EAP-TTLS and is the most used EAP standard after EAP-TLS. In a network with mixed operating systems, PEAP should be the most supported standard after EAP-TLS.
PEAP is similar to EAP-TTLS as it uses a server-side certificate to authenticate clients by creating an encrypted TLS tunnel between the client and the authentication server, which protects the ensuing exchange of authentication information. PEAP authentication differs from EAP-TTLS as it broadcasts the username in the clear and only the password is sent in the encrypted TLS tunnel. EAP-TTLS will use the TLS tunnel for both the username and password.
Add the following lines to
/etc/wpa_supplicant.conf
to
configure the EAP-PEAP related
settings:
This field specifies the EAP method for the connection. | |
The | |
The | |
The | |
This field contains the parameters for the
first phase of authentication, the
TLS tunnel. According to the
authentication server used, specify a specific
label for authentication. Most of the time, the
label will be “client EAP
encryption” which is set by using
| |
This field specifies the authentication
protocol used in the encrypted
TLS tunnel. In the
case of PEAP, it is
|
Add the following to
/etc/rc.conf
:
Then, bring up the interface:
#
service netif start
Starting wpa_supplicant.
DHCPREQUEST on wlan0 to 255.255.255.255 port 67 interval 7
DHCPREQUEST on wlan0 to 255.255.255.255 port 67 interval 15
DHCPREQUEST on wlan0 to 255.255.255.255 port 67 interval 21
DHCPACK from 192.168.0.20
bound to 192.168.0.254 -- renewal in 300 seconds.
wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
ether 00:11:95:d5:43:62
inet 192.168.0.254 netmask 0xffffff00 broadcast 192.168.0.255
media: IEEE 802.11 Wireless Ethernet DS/11Mbps mode 11g
status: associated
ssid freebsdap channel 1 (2412 Mhz 11g) bssid 00:11:95:c3:0d:ac
country US ecm authmode WPA2/802.11i privacy ON deftxkey UNDEF
AES-CCM 3:128-bit txpower 21.5 bmiss 7 scanvalid 450 bgscan
bgscanintvl 300 bgscanidle 250 roam:rssi 7 roam:rate 5 protmode CTS
wme burst roaming MANUALWired Equivalent Privacy (WEP) is part of the original 802.11 standard. There is no authentication mechanism, only a weak form of access control which is easily cracked.
WEP can be set up using ifconfig(8):
#
ifconfig wlan0
create wlandev ath0
#
ifconfig wlan0
inet 192.168.1.100
netmask 255.255.255.0
\
ssid my_net
wepmode on weptxkey 3
wepkey 3:0x3456789012
The weptxkey
specifies which
WEP key will be used in the
transmission. This example uses the third key.
This must match the setting on the access point.
When unsure which key is used by the access point,
try 1
(the first key) for this
value.
The wepkey
selects one of the
WEP keys. It should be in the
format index:key
. Key
1
is used by default; the index
only needs to be set when using a key other than the
first key.
Replace the 0x3456789012
with the key configured for use on the access
point.
Refer to ifconfig(8) for further information.
The wpa_supplicant(8) facility can be used to
configure a wireless interface with
WEP. The example above can be set up
by adding the following lines to
/etc/wpa_supplicant.conf
:
Then:
#
wpa_supplicant -i wlan0
-c /etc/wpa_supplicant.conf
Trying to associate with 00:13:46:49:41:76 (SSID='dlinkap' freq=2437 MHz)
Associated with 00:13:46:49:41:76IBSS mode, also called ad-hoc mode, is
designed for point to point connections. For example, to
establish an ad-hoc network between the machines
A
and B
, choose two
IP addresses and a
SSID.
On A
:
#
ifconfig wlan0
create wlandev ath0
wlanmode adhoc
#
ifconfig wlan0
inet 192.168.0.1
netmask 255.255.255.0
ssid freebsdap
#
ifconfig wlan0
wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
ether 00:11:95:c3:0d:ac
inet 192.168.0.1 netmask 0xffffff00 broadcast 192.168.0.255
media: IEEE 802.11 Wireless Ethernet autoselect mode 11g <adhoc>
status: running
ssid freebsdap channel 2 (2417 Mhz 11g) bssid 02:11:95:c3:0d:ac
country US ecm authmode OPEN privacy OFF txpower 21.5 scanvalid 60
protmode CTS wme burstThe adhoc
parameter indicates that the
interface is running in IBSS mode.
B
should now be able to detect
A
:
#
ifconfig wlan0
create wlandev ath0
wlanmode adhoc
#
ifconfig wlan0
up scan
SSID/MESH ID BSSID CHAN RATE S:N INT CAPS
freebsdap 02:11:95:c3:0d:ac 2 54M -64:-96 100 IS WMEThe I
in the output confirms that
A
is in ad-hoc mode. Now, configure
B
with a different IP
address:
#
ifconfig wlan0
inet 192.168.0.2
netmask 255.255.255.0
ssid freebsdap
#
ifconfig wlan0
wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
ether 00:11:95:d5:43:62
inet 192.168.0.2 netmask 0xffffff00 broadcast 192.168.0.255
media: IEEE 802.11 Wireless Ethernet autoselect mode 11g <adhoc>
status: running
ssid freebsdap channel 2 (2417 Mhz 11g) bssid 02:11:95:c3:0d:ac
country US ecm authmode OPEN privacy OFF txpower 21.5 scanvalid 60
protmode CTS wme burstBoth A
and B
are now
ready to exchange information.
FreeBSD can act as an Access Point (AP) which eliminates the need to buy a hardware AP or run an ad-hoc network. This can be particularly useful when a FreeBSD machine is acting as a gateway to another network such as the Internet.
Before configuring a FreeBSD machine as an AP, the kernel must be configured with the appropriate networking support for the wireless card as well as the security protocols being used. For more details, see Section 31.3.2, “Basic Setup”.
The NDIS driver wrapper for Windows® drivers does not currently support AP operation. Only native FreeBSD wireless drivers support AP mode.
Once wireless networking support is loaded, check if the wireless device supports the host-based access point mode, also known as hostap mode:
#
ifconfig wlan0
create wlandev ath0
#
ifconfig wlan0
list caps
drivercaps=6f85edc1<STA,FF,TURBOP,IBSS,HOSTAP,AHDEMO,TXPMGT,SHSLOT,SHPREAMBLE,MONITOR,MBSS,WPA1,WPA2,BURST,WME,WDS,BGSCAN,TXFRAG>
cryptocaps=1f<WEP,TKIP,AES,AES_CCM,TKIPMIC>This output displays the card's capabilities. The
HOSTAP
word confirms that this wireless
card can act as an AP. Various supported
ciphers are also listed: WEP,
TKIP, and AES. This
information indicates which security protocols can be used
on the AP.
The wireless device can only be put into hostap mode during the creation of the network pseudo-device, so a previously created device must be destroyed first:
#
ifconfig wlan0
destroy
then regenerated with the correct option before setting the other parameters:
#
ifconfig wlan0
create wlandev ath0
wlanmode hostap
#
ifconfig wlan0
inet 192.168.0.1
netmask 255.255.255.0
ssid freebsdap
mode 11g channel 1
Use ifconfig(8) again to see the status of the
wlan0
interface:
#
ifconfig wlan0
wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
ether 00:11:95:c3:0d:ac
inet 192.168.0.1 netmask 0xffffff00 broadcast 192.168.0.255
media: IEEE 802.11 Wireless Ethernet autoselect mode 11g <hostap>
status: running
ssid freebsdap channel 1 (2412 Mhz 11g) bssid 00:11:95:c3:0d:ac
country US ecm authmode OPEN privacy OFF txpower 21.5 scanvalid 60
protmode CTS wme burst dtimperiod 1 -dfsThe hostap
parameter indicates the
interface is running in the host-based access point
mode.
The interface configuration can be done automatically at
boot time by adding the following lines to
/etc/rc.conf
:
192.168.0.1
netmask 255.255.255.0
ssid freebsdap
mode 11g channel 1
"Although it is not recommended to run an AP without any authentication or encryption, this is a simple way to check if the AP is working. This configuration is also important for debugging client issues.
Once the AP is configured, initiate a scan from another wireless machine to find the AP:
#
ifconfig wlan0
create wlandev ath0
#
ifconfig wlan0
up scan
SSID/MESH ID BSSID CHAN RATE S:N INT CAPS
freebsdap 00:11:95:c3:0d:ac 1 54M -66:-96 100 ES WMEThe client machine found the AP and can be associated with it:
#
ifconfig wlan0
inet 192.168.0.2
netmask 255.255.255.0
ssid freebsdap
#
ifconfig wlan0
wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
ether 00:11:95:d5:43:62
inet 192.168.0.2 netmask 0xffffff00 broadcast 192.168.0.255
media: IEEE 802.11 Wireless Ethernet OFDM/54Mbps mode 11g
status: associated
ssid freebsdap channel 1 (2412 Mhz 11g) bssid 00:11:95:c3:0d:ac
country US ecm authmode OPEN privacy OFF txpower 21.5 bmiss 7
scanvalid 60 bgscan bgscanintvl 300 bgscanidle 250 roam:rssi 7
roam:rate 5 protmode CTS wme burstThis section focuses on setting up a FreeBSD AP using the WPA security protocol. More details regarding WPA and the configuration of WPA-based wireless clients can be found in Section 31.3.3.1.3, “WPA”.
The hostapd(8) daemon is used to deal with client authentication and key management on the WPA-enabled AP.
The following configuration operations are performed
on the FreeBSD machine acting as the AP.
Once the AP is correctly working,
hostapd(8) should be automatically enabled at boot
with the following line in
/etc/rc.conf
:
Before trying to configure hostapd(8), first configure the basic settings introduced in Section 31.3.5.1, “Basic Settings”.
WPA-PSK is intended for small networks where the use of a backend authentication server is not possible or desired.
The configuration is done in
/etc/hostapd.conf
:
This field indicates the wireless interface used for the AP. | |
This field sets the level of verbosity during the
execution of hostapd(8). A value of
| |
The | |
The | |
This field sets the network name. | |
The | |
The Warning:Always use strong passwords that are sufficiently long and made from a rich alphabet so that they will not be easily guessed or attacked. | |
The | |
The |
The next step is to start hostapd(8):
#
service hostapd forcestart
#
ifconfig wlan0
wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 2290
inet 192.168.0.1 netmask 0xffffff00 broadcast 192.168.0.255
inet6 fe80::211:95ff:fec3:dac%ath0 prefixlen 64 scopeid 0x4
ether 00:11:95:c3:0d:ac
media: IEEE 802.11 Wireless Ethernet autoselect mode 11g <hostap>
status: associated
ssid freebsdap channel 1 bssid 00:11:95:c3:0d:ac
authmode WPA2/802.11i privacy MIXED deftxkey 2 TKIP 2:128-bit txpowmax 36 protmode CTS dtimperiod 1 bintval 100Once the AP is running, the
clients can associate with it. See Section 31.3.3.1.3, “WPA” for more details.
It is possible to see the stations associated with the
AP using ifconfig
.wlan0
list
sta
It is not recommended to use WEP for setting up an AP since there is no authentication mechanism and the encryption is easily cracked. Some legacy wireless cards only support WEP and these cards will only support an AP without authentication or encryption.
The wireless device can now be put into hostap mode and configured with the correct SSID and IP address:
#
ifconfig wlan0
create wlandev ath0
wlanmode hostap
#
ifconfig wlan0
inet 192.168.0.1
netmask 255.255.255.0
\
ssid freebsdap
wepmode on weptxkey 3
wepkey 3:0x3456789012
mode 11g
The weptxkey
indicates which
WEP key will be used in the
transmission. This example uses the third key as key
numbering starts with 1
. This
parameter must be specified in order to encrypt the
data.
The wepkey
sets the selected
WEP key. It should be in the format
index:key
. If the index is
not given, key 1
is set. The index
needs to be set when using keys other than the first
key.
Use ifconfig(8) to see the status of the
wlan0
interface:
#
ifconfig wlan0
wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
ether 00:11:95:c3:0d:ac
inet 192.168.0.1 netmask 0xffffff00 broadcast 192.168.0.255
media: IEEE 802.11 Wireless Ethernet autoselect mode 11g <hostap>
status: running
ssid freebsdap channel 4 (2427 Mhz 11g) bssid 00:11:95:c3:0d:ac
country US ecm authmode OPEN privacy ON deftxkey 3 wepkey 3:40-bit
txpower 21.5 scanvalid 60 protmode CTS wme burst dtimperiod 1 -dfsFrom another wireless machine, it is now possible to initiate a scan to find the AP:
#
ifconfig wlan0
create wlandev ath0
#
ifconfig wlan0
up scan
SSID BSSID CHAN RATE S:N INT CAPS
freebsdap 00:11:95:c3:0d:ac 1 54M 22:1 100 EPSIn this example, the client machine found the AP and can associate with it using the correct parameters. See Section 31.3.3.1.4, “WEP” for more details.
A wired connection provides better performance and reliability, while a wireless connection provides flexibility and mobility. Laptop users typically want to roam seamlessly between the two types of connections.
On FreeBSD, it is possible to combine two or even more network interfaces together in a “failover” fashion. This type of configuration uses the most preferred and available connection from a group of network interfaces, and the operating system switches automatically when the link state changes.
Link aggregation and failover is covered in Section 31.6, “Link Aggregation and Failover” and an example for using both wired and wireless connections is provided at Example 31.3, “Failover Mode Between Wired and Wireless Interfaces”.
This section describes a number of steps to help troubleshoot common wireless networking problems.
If the access point is not listed when scanning, check that the configuration has not limited the wireless device to a limited set of channels.
If the device cannot associate with an access point, verify that the configuration matches the settings on the access point. This includes the authentication scheme and any security protocols. Simplify the configuration as much as possible. If using a security protocol such as WPA or WEP, configure the access point for open authentication and no security to see if traffic will pass.
Once the system can associate with the access point, diagnose the security configuration using tools like ping(8).
Debugging support is provided by
wpa_supplicant(8). Try running this utility manually
with the -dd
option and look at the
system logs.
There are many lower-level debugging tools.
Debugging messages can be enabled in the 802.11 protocol
support layer using wlandebug(8). On a FreeBSD system
prior to FreeBSD 9.1, this program can be found in
/usr/src/tools/tools/net80211
.
For example, to enable console messages related to
scanning for access points and the 802.11 protocol
handshakes required to arrange communication:
#
wlandebug -i ath0
+scan+auth+debug+assoc
net.wlan.0.debug: 0 => 0xc80000<assoc,auth,scan>Many useful statistics are maintained by
the 802.11 layer and wlanstats
, found
in /usr/src/tools/tools/net80211
,
will dump this information. These statistics should
display all errors identified by the 802.11 layer.
However, some errors are identified in the device drivers
that lie below the 802.11 layer so they may not show up.
To diagnose device-specific problems, refer to the
drivers' documentation.
If the above information does not help to clarify the problem, submit a problem report and include output from the above tools.
All FreeBSD documents are available for download at http://ftp.FreeBSD.org/pub/FreeBSD/doc/
Questions that are not answered by the
documentation may be
sent to <freebsd-questions@FreeBSD.org>.
Send questions about this document to <freebsd-doc@FreeBSD.org>.