We are talking about an access point together with a wlan0 client connection to another wifi network (wlan repeater) or an internet router.
If you want an access point together with an ethernet port eth0 as uplink to a switch or an internet router then look at Setting up a Raspberry Pi as an access point - the easy way.
Tested on a Raspberry Pi 4B with
Raspbian Buster Lite 2019-07-10 updated on 2019-08-13.
Updates done with sudo apt update && sudo apt full-upgrade && sudo reboot
.
Here you will find the last tested revision for Raspbian Stretch Lite.
The Raspberry Pi is able to work as a wireless hotspot and simultanous connect to another hotspot as client. But the wifi device on the RasPi has a general limitation. The client connection cannot be bridged because lack of WDS (wireless distribution system) that is needed for bridging on wireless. For further information look at Raspberry Pi WiFi to Ethernet Bridge for a server?. So we can only use routing for the wifi client connection to the internet router. But the wifi hotspot and the wired ethernet port can be bridged so all devices on wifi and the wired port can have the same broadcast domain on its common subnet.
For reference I use a RPi3B+ with Raspbian Stretch Lite 2019-04-08 and upgraded by sudo bash -c 'apt update && apt full-upgrade && reboot'
on 2019-05-19. I also assume that you already have a connection to the internet. All commands can simply copied and pasted to the command line of the RasPi. The blocks with EOF you can select from cat
incl. the last EOF
and paste it to the RasPis command line. With Enter it will be coppied to a file without the delimiter EOF.
We will first setup a wifi repeater so if anyone only need this he can stop setup at this point and use it. For those who need a bridged ethernet port with the wifi access point can continue with setting it up.
I use systemd-networkd for reasons. For the impatient first only the Setup.
♦ Setup wifi repeater
Example for this setup:
wifi wifi wan
mobile-phone <~.~.~.~.~> (ap0)RPi(wlan0) <.~.~.~.~.> router <───> INTERNET
╲ ╱ ╲
(dhcp 192.168.4.1 (dhcp
from RPi) from router)
Step 1: setup systemd-networkd
For detailed information look at (1). Here only in short. Execute these commands:
# Install hostapd
rpi ~$ sudo -Es
rpi ~# apt install hostapd
rpi ~# systemctl unmask hostapd
rpi ~# systemctl enable hostapd
# disable debian networking and dhcpcd
rpi ~# systemctl mask networking.service dhcpcd.service
rpi ~# sudo mv /etc/network/interfaces /etc/network/interfaces~
rpi ~# sed -i '1i resolvconf=NO' /etc/resolvconf.conf
# enable systemd-networkd
rpi ~# systemctl enable systemd-networkd.service systemd-resolved.service
rpi ~# ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf
Step 2: install hostapd for the access point
Create this file with your settings for ssid=
, country_code=
and wpa_passphrase=
. As channel=
select the same channel wpa_supplicant with wlan0 will connect to your internet router.
ATTENTION! This is a restriction from the hardware. hostapd
will always set the channel to the same value than from the client connection, no matter what you set here. If you need different channels the you have to use an additional USB/WiFi dongle.
rpi ~# cat > /etc/hostapd/hostapd.conf <<EOF
interface=ap0
driver=nl80211
ssid=RPiNet
country_code=DE
hw_mode=g
channel=1
auth_algs=1
wpa=2
wpa_passphrase=verySecretPassword
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
rsn_pairwise=CCMP
EOF
rpi ~# chmod 600 /etc/hostapd/hostapd.conf
Set DAEMON_CONF="/etc/hostapd/hostapd.conf" in /etc/default/hostapd
rpi ~# sed -i 's/^#DAEMON_CONF=.*$/DAEMON_CONF="\/etc\/hostapd\/hostapd.conf"/' /etc/default/hostapd
Edit the hostapd.service:
rpi ~# systemctl --full edit hostapd.service
and comment the line After=network.target
with #
so it looks like:
#After=network.target
Save it and quit the editor. Next add interface ap0 to the hostapd.service with:
rpi ~# systemctl edit hostapd.service
In the empty editor insert these statements, save it and quit the editor:
[Unit]
Wants=wpa_supplicant@wlan0.service
[Service]
ExecStartPre=/sbin/iw dev wlan0 interface add ap0 type __ap
ExecStopPost=-/sbin/iw dev ap0 del
Step 3: setup wpa_supplicant for client connection
Create this file with your settings for country=
, ssid=
and psk=
and enable it:
rpi ~# cat >/etc/wpa_supplicant/wpa_supplicant-wlan0.conf <<EOF
country=DE
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
network={
ssid="TestNet"
psk="realyNotMyPassword"
key_mgmt=WPA-PSK # see ref (4)
}
EOF
rpi ~# chmod 600 /etc/wpa_supplicant/wpa_supplicant-wlan0.conf
rpi ~# systemctl disable wpa_supplicant.service
rpi ~# systemctl enable wpa_supplicant@wlan0.service
Extend wpa_supplicant with:
rpi ~# systemctl edit wpa_supplicant@wlan0.service
In the empty editor insert these statements. Have attention to the minus sign after equal =-
on some statements. Save it and quit the editor:
[Unit]
BindsTo=hostapd.service
After=hostapd.service
[Service]
ExecStartPost=/sbin/iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE
ExecStopPost=-/sbin/iptables -t nat -D POSTROUTING -o wlan0 -j MASQUERADE
Step 4: setup static interfaces
Create these files:
rpi ~# cat > /etc/systemd/network/08-wlan0.network <<EOF
[Match]
Name=wlan0
[Network]
IPForward=yes
# If you need a static ip address, then toggle commenting next four lines (example)
DHCP=yes
#Address=192.168.10.60/24
#Gateway=192.168.10.1
#DNS=84.200.69.80 1.1.1.1
EOF
For those who want a bridge, do not need the next file and must continue with Setup bridge.
rpi ~# cat > /etc/systemd/network/12-ap0.network <<EOF
[Match]
Name=ap0
[Network]
Address=192.168.4.1/24
DHCPServer=yes
[DHCPServer]
DNS=84.200.69.80 1.1.1.1
EOF
Setup a wifi repeater without bridge is finished. You must
Reboot.
♦ Setup bridge
Setup wifi repeater as described above.
Example for this setup:
(dhcp
from RPi) bridge
╱ wifi ┌──────┐
mobile-phone <~.~.~.~.> │(ap0) │ wifi wan
│ br0│RPi(wlan0) <.~.~.~.~> router <───> INTERNET
laptop <────────> |(eth0)│╲ ╲
╲ wired └──────┘╱ (dhcp
(dhcp 192.168.4.1 from router)
from RPi)
Step 5: configure hostapd for a bridge
Add a line bridge=br0
to /etc/hostapd/hostapd.conf with:
rpi ~# echo 'bridge=br0' >> /etc/hostapd/hostapd.conf
Step 6: setup wpa_supplicant for a bridge
Extend wpa_supplicant with:
rpi ~# systemctl edit wpa_supplicant@wlan0.service
In the editor add 3 lines so it looks like following. Have attention to the minus sign after equal =-
on some statements. Save it and quit the editor:
[Unit]
BindsTo=hostapd.service
After=hostapd.service
Wants=ap-bring-up.service
Before=ap-bring-up.service
[Service]
ExecStartPost=/sbin/iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE
ExecStopPost=-/sbin/iptables -t nat -D POSTROUTING -o wlan0 -j MASQUERADE
ExecStopPost=-/bin/ip link set ap0 up
Please note that ExecStopPost=-/bin/ip link set ap0 up
is not a typo. On stopping wpa_supplicant, interface ap must be set up again as described in section Details - wpa_supplicant for bridge (Step 6).
Step 7: bring up access point with virtual wifi interface
Create a unit with:
rpi ~# systemctl --force --full edit ap-bring-up.service
In the empty editor insert these statements, save it and quit the editor:
[Unit]
Description=Bring up wifi interface ap0
Requisite=hostapd.service
[Service]
Type=oneshot
ExecStart=/lib/systemd/systemd-networkd-wait-online --interface=wlan0 --timeout=60 --quiet
ExecStartPost=/bin/ip link set ap0 up
Step 8: setup static interfaces
For a bridge ap0 is dynamically created. So create these files:
rpi ~# cat > /etc/systemd/network/02-br0.netdev <<EOF
[NetDev]
Name=br0
Kind=bridge
EOF
rpi ~# cat > /etc/systemd/network/04-eth0.network <<EOF
[Match]
Name=eth0
[Network]
Bridge=br0
EOF
rpi ~# cat > /etc/systemd/network/16-br0_up.network <<EOF
[Match]
Name=br0
[Network]
Address=192.168.4.1/24
DHCPServer=yes
[DHCPServer]
DNS=84.200.69.80 1.1.1.1
EOF
Reboot.
That's it.
♦ Details
General
One problem is that we want to use the same device for a wifi client and for an access point. This must be supported by the wifi hardware. We can check this with
rpi ~$ sudo iw list | grep -A4 "valid interface combinations:"
valid interface combinations:
* #{ managed } <= 1, #{ P2P-device } <= 1, #{ P2P-client, P2P-GO } <= 1,
total <= 3, #channels <= 2
* #{ managed } <= 1, #{ AP } <= 1, #{ P2P-client } <= 1, #{ P2P-device } <= 1,
total <= 4, #channels <= 1
The important part is #{ managed } <= 1, #{ AP } <= 1,
but you can also see that this is only possible on one channel.
I've found that we have to setup this in sequence, otherwise it won't work. If other applications bind to the wifi port it cannot be set.
- create a virtual interface
ap0
for the access point
- start access point daemon
hostapd
using interface ap0
- start
wpa_supplicant
for wifi client using interface wlan0
This order restricts the whole setup. It isn't possible to start hostapd when wpa_supplicant is running. You must first stop wpa_supplicant and then start hostapd and wpa_supplicant in this order. This is due to the WiFi driver brcmfmac
.
Another quirks is that wpa_supplicant disables the interface ap0 when it is managed, no matter if it start or stop. So even after a start from wpa_supplicant we have to enable ap0 again.
Here are mainly five components involved: virtual interface ap0, hostapd, wpa_supplicant, setup bridge and bring up access point.
hostapd (Step 2)
This is the normal setup you will find all over the web. Please set the channel to the same value than wlan0 is connected to the wifi from your router. It is the restriction from the hardware and may avoid confusion with channel setting. hostapd will always set the channel to the same value than from the client connection, no matter what you set here.
Please use a passphrase that is long enough, I would say at least with 8 characters. It was told that 4 characters are to small and hostapd will refuse to accept connections. You will not find the access point RPiNet in your mobile phone (thanks to @Leo).
For dependencies we extend the unit from hostapd with a drop in file (overlay) (2). It always starts wpa_supplicant (Wants it) and creates interface ap0 before starting hostapd. This is respected to the starting order. Because ap0 is bound to wlan0 it gets the same mac address. You may consider to give it a unique mac address but that's not a good idea. On the network is only seen the mac address from wlan0. If you give ap0 its own mac address then it is not seen on the network for arp requests and the ip address for connections to ap0 is not found and get stuck. You have to set ap0 to promiscuous mode to get it to work then.
After setting up the dependencies then the hostapd.service by default will start After=network.target
. The wpa_supplicant@wlan0.service must start After=hostapd.service
and starts by default Before=network.target
. Do you see the conflict with network.target
? Systemd complains it with the error message "Found ordering cycle on wpa_supplicant@wlan0.service/start" and prevents hostapd.service to start. That's the reason why we have do comment After=network.target
in the unit file of the hostapd.service.
After stopped hostapd then ap0 is also deleted so it can be created again on next start of hostapd.
wpa_supplicant (Step 3)
Setting up wpa_supplicant for wlan0 we do as usual. It's extended unit is to strictly bind wpa_supplicant to hostapd so it will start and stop with it in the right order. We do it because running wpa_supplicant without hostapd is very complicated and may result in a total crash of the brcmfmac wifi driver, I have seen that on my tests.
There is no need that clients connected to the internet router must also connect to clients on the access point. So we can use NAT that simplifies setup a lot. Then we don't have to configure static routes and it is not needed to configure wlan0 with static values (ip address, gateway, DNS server etc.).
Setup static interfaces (Step 4)
Here we define interface wlan0 and the virtual interface ap0 we need for a wifi repeater. For wlan0 we get an ip address by DHCP from the internet router. Optional you can set a static ip address, but then you also have to define all other settings like gateway and DNS server because you don't get them anymore from the DHCP server. IP forward is also enabled here that we use for routing between wlan0 and ap0.
Interface ap0 needs a static ip address because it is the access point and the source of the DHCP server for the wifi network.
hostapd for bridge (Step 5)
We have setup hostapd in Step 2. Now we only need to append bridge=br0
to its configuration so that it will dynamically manage adding ap0 to the bridge.
wpa_supplicant for bridge (Step 6)
When wpa_supplicant is started it also brings up interface wlan0. Every time it is managed, no matter if started or stopped, it will stop ap0 because it is not a real interface and depends direct on wlan0. That is also the reason why it can only brought up when wlan0 has Gained carrier. But we cannot just wait some seconds and then bring up ap0. wpa_supplicant.service must have started completely so we only can use an extra service ap-bring-up.service for doing this. The dependencies ensure this.
After stopped wpa_supplicant (bring wlan0 down) ap0 must brought up again so it can continue running for the access point.
bring up access point (Step 7)
It is not possible to just set up ap0 when needed. It can only start when wlan0 "Gained carrier" and link becomes ready (3). This will happen some or more seconds after wpa_supplicant has started. So we need ap-bring-up.service that wpa_supplicant Wants and that will check if wlan0 has "Gained carrier" and is online. There is a helper systemd-networkd-wait-online that can do this synchronous. We use it with a timeout of 60 seconds. If your network connection takes longer than 60 seconds to get up, then you should increase the timeout accordingly. With journalctl -b -e
you can check if Starting Bring up wifi interface ap0...
and Started Bring up wifi interface ap0.
covers wlan0: Gained carrier
. This is very important because otherwise the bridge will not work correctly with undefined behavior. And of course this unit should only start when hostapd is running (Requisite).
define static interfaces for bridge (Step 8)
This files define the bridge. ap0 will dynamically added by hostapd. eth0 and ap0 are slaves of the bridge and don't need an ip address. The bridge br0 itself also does not need an ip address but here it has a static ip address because we need it for the DHCP server bound to br0 so the DHCP server is available on the subnet on the bridge ( interfaces eth0, ap0).
Conclusion
You are now able to start, stop and restart hostapd and wpa_supplicant.
You should see the access point, here RPiNet, in your mobile phone and should get an ip address to connect to the access point. You should also get an ip address from the same subnet if you connect a laptop with an cable to the ethernet port and you can ping the mobile phone.
With this setup you have the following dependencies with starting and stopping:
hostapd │ wpa_supplicant wpa_supplicant │ hostapd
───────────┼────────────────────────────────────┼──────────
starting │ starts starting │ starts
stopping │ stops stopping │ ----
restarting │ restarts restarting │ starts
This is because of the strict order of starting (see section General). You cannot run wpa_supplicant without hostapd but you can run hostapd without wpa_supplicant by starting hostapd and then stop wpa_supplicant.
If communication stops for some reason (e.g. delay to small or something else) it is mostly enough to kick ap0 with /bin/ip link set ap0 up
.
refefences:
[1] Howto migrate from networking to systemd-networkd with dynamic failover
[2] man systemd.unit
[3] systemd-networkd wireless bridging - need to wait for carrier
[4] Setup WiFi on Pi 3 B+