Sharing a 3G connection with Ubuntu

Seeing as I carry around a vast array of equipment, in my massive, 10Ton backpack, I normally have a 3G card at hand. If I’m visiting someone who doesn’t have broadband themselves, or I’m sitting in a Coffee Shop with other laptop-lugging friends I might want to share my 3G connection with friends, via WiFi. (assuming I have a data bundle that month, or they understand the horrific 3G data pricing)

I wrote a little script to make this easy

  • It’s clearly Atheros-specific, but I’ve included more generic commands in comments. Obviously interface names would need to be changed
  • I dial the 3G connection before I run this, and disconnect afterwards, but it would be trivial to change that…
  • My dnsmasq.conf contains only the line dhcp-range=,,12h
  • Dnsmasq is configured not to run on startup, via update-rc.d



/etc/dbus-1/event.d/25NetworkManager stop
# Atheros:
wlanconfig ath0 destroy
wlanconfig ath0 create wlandev wifi0 wlanmode ap
# Other:
#iwconfig ath1 mode master

iwconfig ath0 chan 3
iwconfig ath0 essid SR
iwconfig ath0 enc s:13Char-Passwd

ifconfig ath0 up netmask
/etc/init.d/dnsmasq start

iptables -t nat -F POSTROUTING
iptables -t nat -A POSTROUTING -o ppp0 -s -j MASQUERADE
sysctl -w net/ipv4/ip_forward=1

echo "Done - when finished, hit enter"
read ignoreme

/etc/init.d/dnsmasq stop
iptables -t nat -F POSTROUTING
sysctl -w net/ipv4/ip_forward=0

# Atheros:    
wlanconfig ath0 destroy
wlanconfig ath0 create wlandev wifi0 wlanmode sta
# Other:
#iwconfig ath0 mode managed

/etc/dbus-1/event.d/25NetworkManager start


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Thanks so much, that was very simple, and worked for me. :-)

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