• get raspberry pi 2
• setup ubuntu
• get usb wifi dongle that supports master (AP) mode, e.g. with RT5370 chip. Search on Amazon

This is based on WiFi AP (RT5370) on Raspberry Pi

don't forget to adjust to your adapters: eth0 and wlan1 used here

• sudo su -, opens root console, that redirect > works
• lsusb, should show 148f:5370 Ralink Technology, Corp. RT5370 Wireless Adapter
• apt-get install hostapd dnsmasq
• nano /etc/network/interfaces

allow-hotplug wlan1
iface wlan1 inet static
  address 10.10.10.1
  netmask 255.255.255.0

#wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
iface default inet manual

• nano /etc/hostapd/hostapd.conf

interface=wlan1
driver=nl80211
ssid=MAPBOX-STUDIO-PROXY
hw_mode=g
channel=6
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=2
wpa_passphrase=MY_SUPER_SECRET_PASSWORD
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
rsn_pairwise=CCMP

• nano /etc/default/hostapd

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

• /etc/init.d/hostapd restart
• update-rc.d hostapd enable
• nano /etc/dnsmasq.conf

interface=wlan1 
except-interface=eth0
dhcp-range=10.10.10.2,10.10.10.150,255.255.255.0,12h

• /etc/init.d/dnsmasq restart
• update-rc.d dnsmasq enable
• nano /etc/sysctl.conf
  • uncomment net.ipv4.ip_forward=1
• sysctl -p
• iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
• iptables -A FORWARD -i eth0 -o wlan1 -m state --state RELATED,ESTABLISHED -j ACCEPT
• iptables -A FORWARD -i wlan1 -o eth0 -j ACCEPT
• iptables-save > /etc/iptables.nat
• echo '#!/bin/bash' > /etc/network/if-up.d/forwarding && echo 'iptables-restore < /etc/iptables.nat' >> /etc/network/if-up.d/forwarding && chmod +x /etc/network/if-up.d/forwarding
• shutdown -r now

The author of WiFi AP (RT5370) on Raspberry Pi states that it doesn't work after a reboot. He solved it with:

• nano /etc/default/ifplugd

INTERFACES="eth0"
HOTPLUG_INTERFACES="eth0"
ARGS="-q -f -u0 -d10 -w -I"
SUSPEND_ACTION="stop"

Didn't work for me.

However, reissuing iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE after reboot works for me.

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