RaspberryPi/Hotspot

This page covers the use of a Raspberry Pi to act as an AP/Wifi hotspot.

The basic steps covered here are:

• Install software for DNS, DHCP, and AP-hosting
• Configure DHCP
• Configure DNS

Install Software

Install DNS, DHCP, and AP-hosting software:

sudo apt install dnsmasq dhcpcd5 hostapd

Set up DHCP

For dhcp we'll use the dhcpcd utility.

Edit dhcpcd config file

Edit /etc/dhcpcd.conf and modify it to contain this:

interface wlan1
    static ip_address=192.168.4.1/24
    nohook wpa_supplicant

replace wlan1 with whatever interface you want to use.

Restart dhcpcd service

sudo service dhcpcd restart

DNS

DNS is handled by the dnsmasq utility.

Edit dnsmmasq config file

Edit the dnsmasq config file /etc/dnsmasq.conf, which determines what range of IP addresses will be handed out and for how long. Modify it to contain this:

interface=wlan1
dhcp-range=192.168.4.2,192.168.4.20,255.255.255.0,24h

This will hand out IPs starting at 192.168.4.2 and ending at 192.168.4.20, lasting for 24 hours lease time.

Modify wlan0 to whatever interface you are using to provide the wifi network.

Restart dnsmasq service

If you are installing dnsmasq fresh, enable then start the service:

sudo systemctl enable dnsmasq
sudo systemctl start dnsmasq

or reload/restart the service:

sudo systemctl reload dnsmasq

Troubleshooting

Preferred DNS Resolver

Was experiencing problems with reaching the wider internet because of DNS problems:

ping: google.com: Temporary failure in name resolution

Solved this by doing the following:

Following this comment I tried to figure out what was happening with /etc/resolv.conf.

On my system it was a link, to something in /etc/resolvconf/.... I discovered there was a service called resolvconf by running service --status-all.

I disabled the resolvconf service by running the command:

service disable resolvconf

then remove the existing file at /etc/resolv.conf (we will replace it with our own one-line file):

rm -f /etc/resolv.conf

Now edit that file

vim /etc/resolv.conf

paste the contents

nameserver 1.1.1.1
nameserver 8.8.8.8

or whatever other nameservers you want to use.

Host an AP

We use hostapd to create the necessary infrastructure to host an access point.

Edit hostapd config file

Now modify the file /etc/hostapd/hostapd.conf to configure hostapd. Modify the contents to the following:

interface=wlan0
driver=nl80211
ssid=MyLittlePony
hw_mode=g
channel=7
wmm_enabled=0
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=2
wpa_passphrase=AardvarkBadgerHedgehog
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
rsn_pairwise=CCMP

Note values for hw_mode are:

• a = IEEE 802.11a (5 GHz)
• b = IEEE 802.11b (2.4 GHz)
• g = IEEE 802.11g (2.4 GHz)

Specify location of hostapd file

Modify the file /etc/default/hostapd to read:

DAEMON_CONF="/etc/hostapd/hostapd.conf"

Restart hostapd

sudo systemctl unmask hostapd
sudo systemctl enable hostapd
sudo systemctl start hostapd

Check status and ensure running ok:

sudo systemctl status hostapd
sudo systemctl status dnsmasq

Troubleshooting hostapd

If something fails it will probably be on the start step:

$ sudo systemctl start hostapd
Job for hostapd.service failed because the control process exited with error code.
See "systemctl status hostapd.service" and "journalctl -xe" for details.

Strategy for Debugging

For startup problems, you'll use journalctl -xe or your syslog to find the errors.

If hostapd is up and running okay, then you can debug problems with it using the following procedure. In one window, run this command to run hostapd in the foreground:

hostapd -d /etc/hostapd/hostapd.conf

In another window, monitor the system log:

tail -f /var/log/syslog

Now try connecting to the wifi access point that you created. This should generate some useful/interesting events in the log.

Link is not ready/Driver initialization failed

This is a problem that happens before hostapd starts. Here is the problem I encountered:

-- Logs begin at Thu 2019-02-14 10:12:02 UTC, end at Sun 2019-11-24 09:30:31 UTC. --
Nov 24 09:27:18 raspberry-pi hostapd[1225]: nl80211: deinit ifname=wlan1 disabled_11b_rates=0
Nov 24 09:27:18 raspberry-pi NetworkManager[154]: <info>  [1574587638.4191] device (wlan1): supplicant interface
state: inactive -> disabled
Nov 24 09:27:18 raspberry-pi kernel: IPv6: ADDRCONF(NETDEV_UP): wlan1: link is not ready
Nov 24 09:27:18 raspberry-pi NetworkManager[154]: <info>  [1574587638.8258] device (wlan1): supplicant interface
state: disabled -> inactive
Nov 24 09:27:18 raspberry-pi hostapd[1225]: nl80211 driver initialization failed.
Nov 24 09:27:18 raspberry-pi hostapd[1225]: wlan1: interface state UNINITIALIZED->DISABLED
Nov 24 09:27:18 raspberry-pi hostapd[1225]: wlan1: AP-DISABLED
Nov 24 09:27:18 raspberry-pi hostapd[1225]: wlan1: CTRL-EVENT-TERMINATING
Nov 24 09:27:18 raspberry-pi hostapd[1225]: hostapd_free_hapd_data: Interface wlan1 wasn't started
Nov 24 09:27:18 raspberry-pi systemd[1]: hostapd.service: Control process exited, code=exited, status=1/FAILURE

The solution to the problem is to bring down the wlan1 interface, disable the network manager, and then start hostapd.

service hostapd stop
service network-manager stop
ifconfig wlan1 down
rfkill unblock wlan
service hostapd stop
service hostapd start

Link: https://askubuntu.com/questions/472794/hostapd-error-nl80211-could-not-configure-driver-mode/743127#743127

Cannot open PID file

Another error I encountered was hostapd not being able to open PID file:

$ journalctl -xe
Nov 24 09:38:50 raspberry-pi hostapd[1708]: Configuration file: /etc/hostapd/hostapd.conf
Nov 24 09:38:50 raspberry-pi kernel: IPv6: ADDRCONF(NETDEV_UP): wlan1: link is not ready
Nov 24 09:38:50 raspberry-pi hostapd[1708]: Using interface wlan1 with hwaddr 36:28:03:71:17:5b and ssid "MyLittlePony"
Nov 24 09:38:51 raspberry-pi kernel: IPv6: ADDRCONF(NETDEV_CHANGE): wlan1: link becomes ready
Nov 24 09:38:51 raspberry-pi hostapd[1708]: wlan1: interface state UNINITIALIZED->ENABLED
Nov 24 09:38:51 raspberry-pi hostapd[1708]: wlan1: AP-ENABLED
Nov 24 09:38:51 raspberry-pi systemd[1]: hostapd.service: Can't open PID file /run/hostapd.pid (yet?) after start: No such file or directory
Nov 24 09:38:51 raspberry-pi systemd[1]: Started Advanced IEEE 802.11 AP and IEEE 802.1X/WPA/WPA2/EAP Authenticator.

Packet received on interface that has no address

Problem with error message "DHCP packet received on wlan1 which has no address":

Nov 24 10:04:33 raspberry-pi hostapd: wlan1: STA d0:04:01:81:88:00 IEEE 802.11: authenticated
Nov 24 10:04:33 raspberry-pi hostapd: wlan1: STA d0:04:01:81:88:00 IEEE 802.11: associated (aid 1)
Nov 24 10:04:33 raspberry-pi hostapd: wlan1: STA d0:04:01:81:88:00 RADIUS: starting accounting session BB7B0D32203238F1
Nov 24 10:04:33 raspberry-pi hostapd: wlan1: STA d0:04:01:81:88:00 WPA: pairwise key handshake completed (RSN)
Nov 24 10:04:33 raspberry-pi dnsmasq-dhcp[1023]: DHCP packet received on wlan1 which has no address
Nov 24 10:04:35 raspberry-pi dnsmasq-dhcp[1023]: DHCP packet received on wlan1 which has no address
Nov 24 10:04:39 raspberry-pi dnsmasq-dhcp[1023]: DHCP packet received on wlan1 which has no address
Nov 24 10:04:48 raspberry-pi dnsmasq-dhcp[1023]: DHCP packet received on wlan1 which has no address
Nov 24 10:05:02 raspberry-pi CRON[1817]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1)
Nov 24 10:05:04 raspberry-pi dnsmasq-dhcp[1023]: DHCP packet received on wlan1 which has no address

Underlying issue was with DHCP not working. I was able to see the wifi AP being broadcast, and try to connect to it, but was failing to get assigned an IP address. This was an indication the problem was with the DHCP service.

Turns out, it wasn't running. To start the DHCP service:

service dhcpcd restart

Next Steps

• RaspberryPi/OpenVPN for setting up OpenVPN on the Raspberry Pi

References

Links

• https://www.raspberrypi.org/documentation/configuration/wireless/access-point.md