Software access point
A software access point, also called virtual router or virtual Wi-Fi, enables a computer to turn its wireless interface into a Wi-Fi access point. It saves the trouble of getting a separate wireless router.
Requirements
Wi-Fi device must support AP mode
You need a nl80211 compatible wireless device, which supports the AP operating mode. This can be verified by running the iw list
command, under the Supported interface modes
block there should be AP
listed:
$ iw list
Wiphy phy1 ... Supported interface modes: * IBSS * managed * AP * AP/VLAN * WDS * monitor * mesh point ...
Wireless client and software AP with a single Wi-Fi device
Creating a software AP is independent from your own network connection (Ethernet, wireless, ...). Many wireless devices even support simultaneous operation both as AP and as wireless "client" at the same time. Using that capability you can create a software AP acting as a "wireless repeater" for an existing network, using a single wireless device. The capability is listed in the following section in the output of iw list
:
$ iw list
Wiphy phy1 ... valid interface combinations: * #{ managed } <= 2048, #{ AP, mesh point } <= 8, #{ P2P-client, P2P-GO } <= 1, total <= 2048, #channels <= 1, STA/AP BI must match ...
The constraint #channels <= 1
means that your software AP must operate on the same channel as your Wi-Fi client connection; see the channel
setting in hostapd.conf
below.
If you want to use the capability/feature, perhaps because an Ethernet connection is not available, you need to create two separate virtual interfaces for using it.
Virtual interfaces for a physical device wlan0
can be created as follows:
The virtual interfaces with unique MAC address are created for the network connection (wlan0_sta
) itself and for the software AP/hostapd "wireless repeater":
# iw dev wlan0 interface add wlan0_sta type managed addr 12:34:56:78:ab:cd # iw dev wlan0 interface add wlan0_ap type managed addr 12:34:56:78:ab:ce
These can be made persistent using systemd.netdev(5) as described in BBS#236923. Alternatively if systemd-networkd is not in use, a systemd unit file can be created:
/etc/systemd/system/create-virtual-interface.service
[Unit] Description=Create virtual wireless interface Requires=sys-subsystem-net-devices-wlan0.device After=network.target After=sys-subsystem-net-devices-wlan0.device [Service] Type=oneshot ExecStart=/usr/bin/iw dev wlan0 interface add wlan0_ap type managed addr "12:34:56:78:ab:ce" [Install] WantedBy=multi-user.target
Random MAC address can be generated using macchanger.
Configuration
Setting up an access point consists of two main parts:
- Setting up the Wi-Fi link layer, so that wireless clients can associate to your computer's software access point and exchange IP packets with it.
- Setting up the network configuration on your computer, so that it properly relays IP packets between its own internet connection and the wireless clients.
Wi-Fi link layer
The actual Wi-Fi link is established via the hostapd package, which has WPA2 support.
hostapd comes with a default configuration file which includes numerous options listed and corresponding descriptions, you might want to take a look to gather some basic knowledge.
Adjust the options in hostapd configuration file if necessary. Especially, change the ssid
and the wpa_passphrase
. ieee80211ac
and ieee80211ax
can be enabled for latest WiFi5 and WiFi6 adapters. The option ht_capab
affects your AP's capabilities including channel width which is important to transfer speed.
See hostapd Linux documentation page for more information.
/etc/hostapd/hostapd.conf
interface=wlan0_ap bridge=br0 # SSID to be used in IEEE 802.11 management frames ssid=YourWiFiName # Driver interface type (hostap/wired/none/nl80211/bsd) driver=nl80211 # Country code (ISO/IEC 3166-1) country_code=US # Operation mode (a = IEEE 802.11a (5 GHz), b = IEEE 802.11b (2.4 GHz) hw_mode=g # Channel number channel=7 # Maximum number of stations allowed max_num_sta=5 # Bit field: bit0 = WPA, bit1 = WPA2 wpa=2 # Bit field: 1=wpa, 2=wep, 3=both auth_algs=1 # Set of accepted cipher suites; disabling insecure TKIP wpa_pairwise=CCMP # Set of accepted key management algorithms wpa_key_mgmt=WPA-PSK wpa_passphrase=Somepassphrase # hostapd event logger configuration logger_stdout=-1 logger_stdout_level=2 ## Enable 802.11n support #ieee80211n=1 ## Enable 802.11ac support #ieee80211ac=1 ## Enable 802.11ax support #ieee80211ax=1 ## QoS support #wmm_enabled=1 ## Use "iw list" to show device capabilities and modify ht_capab and vht_capab accordingly #ht_capab=[HT40+][SHORT-GI-40][TX-STBC][RX-STBC1][DSSS_CCK-40] #vht_capab=[RXLDPC][SHORT-GI-80][TX-STBC-2BY1][RX-STBC-1]
utf8_ssid=1
. Some clients may have problems with recognizing the correct encoding (e.g. wpa_supplicant or Windows 7).For automatically starting hostapd on boot, enable the hostapd.service
.
If you are starting hostapd on boot, make sure the wireless network interface is brought up first, otherwise it will fail. To ensure your wireless interface is ready, edit the unit configuration file and state that it is bound to and should start after your network interface:
/etc/systemd/system/hostapd.service.d/override.conf
[Unit] BindsTo=sys-subsystem-net-devices-wlan0.device After=sys-subsystem-net-devices-wlan0.device
Also make sure that the interface is not managed by other network managers. If you are using NetworkManager, see NetworkManager#Ignore specific devices.
driver=nl80211
with driver=rtl871xdrv
in the hostapd.conf
file.Network configuration
There are two basic ways for implementing this:
- bridge: creates a network bridge on your computer, wireless clients will appear to access the same network interface and the same subnet that is used by your computer.
- NAT: with IP forwarding/masquerading and DHCP service, wireless clients will use a dedicated subnet, data from/to that subnet is NAT-ted. This is similar to a normal Wi-Fi router which is connected to the internet.
The bridge approach is simpler, but it requires that any service that is needed by the wireless clients, in particular DHCP, is available on the computer's external interface. This means it will not work if the external modem which assigns IP addresses, supplies the same one to different clients.
The NAT approach is more versatile, as it clearly separates Wi-Fi clients from your computer and it is completely transparent to the outside world. It will work with any kind of network connection, and (if needed) traffic policies can be introduced using the usual iptables approach.
It is possible to combine these two approaches: for example having a bridge that contains both an ethernet device and the wireless device with a static ip, offering DHCP and setting NAT configured to relay the traffic to an additional network device connected to the WAN.
Bridge setup
You need to create a network bridge and add your network interface (e.g. eth0
) to it. You should not add the wireless device (e.g. wlan0
) to the bridge; hostapd will add it on its own.
See Network bridge.
NAT setup
See Internet sharing#Configuration for configuration details.
In that article, the device connected to the LAN is net0
. That device would be in this case your wireless device (e.g. wlan0
).
Tools
linux-wifi-hotspot
The linux-wifi-hotspotAUR package provides a script that can create either a bridged or a NATed access point for internet sharing. It combines hostapd, dnsmasq and iptables for the good functioning of the access point. Includes both command line and gui. The basic syntax to create a NATed virtual network is the following:
# create_ap wlan0 eth0 MyAccessPoint MyPassPhrase
Alternatively, the template configuration provided in /etc/create_ap.conf
can be adapted to ones need and the script run with:
# create_ap --config /etc/create_ap.conf
To use the GUI, run in terminal:
# wihotspot
Enable/start the create_ap.service
to run the script at boot time with the configuration specified in /etc/create_ap.conf
.
For more information see linux-wifi-hotspot on GitHub.
RADIUS
See [1][dead link 2024-03-03 ⓘ] for instructions to run a FreeRADIUS server for WPA2 Enterprise.
Troubleshooting
WLAN is very slow
Frequent causes for a lower than expected throughput include
- An improper choice of operation mode with a
hw_mode
lower than the one supported can limit the router artificially. Check that a modern operating mode is selected. - A crowded or otherwise noise afflicted
channel
can severely degrade performance especially in densely populated areas. Try changing to a different channel or even switch frequencies.
NetworkManager is interfering
hostapd may not work, if the device is managed by NetworkManager. You can mask the device using MAC:
/etc/NetworkManager/conf.d/unmanaged.conf
[keyfile] unmanaged-devices=mac:hwaddr
Or interface name:
/etc/NetworkManager/conf.d/unmanaged.conf
[keyfile] unmanaged-devices=interface-name:ifname
Cannot start AP mode in 5 GHz band
Apparently with the special country code 00
(global), all usable frequencies in the 5Ghz band will have the no-ir
(no-initiating-radiation) flag set, which will prevent hostapd from using them. You will need to have wireless-regdb installed and have your country code set to make frequencies allowed in your country available for hostapd.
Note that recent Intel devices have a Location-Aware Regulatory (LAR) feature, which ignores the userspace regulatory database and instead deduces the regulatory region by listening to other nearby access points. This means the devices will not transmit on any 5 GHz frequencies until they have first seen other access points on the 5 GHz frequency bands, preventing any 5 GHz transmission at all in many cases. Older kernels had an option to disable this which was removed in 2019 due to it causing the firmware to crash. Since this removal, Intel cards supporting LAR can no longer be used as access points in the 5 GHz band.
Windows 10+ refuses to connect with hostapd using WPA3
Windows seems to refuse connecting to WPA3 access points with hostapd. Using wpa=2
instead of wpa=3
may solve the issue.
Access point does not accept running in 40Mhz mode (HT)
You may receive the following message:
20/40 MHz operation not permitted on channel pri=13 sec=9 based on overlapping BSSes
That means that too many nearby access points are detected by your WIFI device. It then refuses to use more than 20Mhz channel width in order to share more fairly the wireless spectrum.
You may be able to disable that with noscan=1
, but that may likely violate local regulatory requirements.