Making a Raspberry Pi 3G Bridge / Hotspot

This post documents making a 3G Internet bridge / hotspot from a Raspberry Pi, a 3G modem, and a separate WiFi access point.

The purpose was to create an Internet connected WiFi-network at my parents' summer cottage.

I want to cover a fairly large area of the property and house. I might want several WiFi access points and control their placement and the placement of the 3G modem, therefore I did not want an integrated WiFi hub such as a Dovado 3/4G router (SEK 799 / €92 at Kjell & Co.

I'm using:

• a Raspberry Pi model B (SEK 298 / €34 at Webhallen)
• the Adafruit Occidentalis v 0.2 distribution (since I'd used it before)
• an unlocked Huawei HiLink E353, originally tied to Swedish operator Tre, I think (SEK 179 / €21 at Swedish auction site Tradera)
• Connected a WiFi access point I had earlier to the Raspberry Pi.
• My plan is to use Telenor Bredband Kontant (SEK 400 / €46 for 6 months and 10 GB data). I did my tests by borrowing the SIM card from my iPad.
• I think I also need a powered USB hub for the 3G modem, will experiment later to see if a more powerful supply for the Raspberry Pi might remove the need for this.
• Normally, I used ssh over a network connection to the Raspberry Pi, but when setting up the network bridge, I used a regular monitor (with an HDMI - DVI cable) and a USB keyboard, because the network interfaces must be shut down to set up the bridge.

Installed Occidentalis on the SD card.

Connected RasPi to MacBook with Ethernet cable. Internet sharing from WiFi to Ethernet on MacBook, to give RasPi Internet access. Logged in with ssh on Raspberry Pi.

Booted the RasPi.

Did:

sudo apt-get update
sudo apt-get upgrade

(takes a long time)

usb_modeswitch is required to get 3G modem to work:

apt-get install usb-modeswitch

Install UPnP client, will be needed to open ports in the modem:

apt-get install miniupnpc

Remove and re-insert dongle?

Reboot:

sudo shutdown -r now

On startup, stick should be available as eth1, check with ifconfig. If it doesn't it might be that the modem needs to be in a powered USB hub.

edit /etc/network/interfaces

Add:

iface eth1 inet dhcp 

check with:

sudo ifup eth1

Great. Try to ssh into RasPi over public internet. How to get public IP?

wget http://ipecho.net/plain -O - -q ; echo

Got 90.129.85.242

Can't ssh to it (connection refused). After some research found out that in order to open port forwarding on the 3G modem, one must use UPnP.

Open port 22 to allow ssh connections from the Internet to the Raspberry Pi.

// to receive ssh

upnpc -r 22 TCP

Set up bridge (for more information, see documentation). This entails shutting down both network interfaces, so you will need to be connected to the Pi with keyboard & monitor, or with a third network connection:

I think I shut down eth0 and eth1 first:

ifdown eth0
ifdown eth1 

Then set up the bridge:

brctl addbr br0
brctl addif eth0
brctl addif eth1
dhclient br0

It works! Can access Internet via Dongle from WiFi. 

Modified my WiFi access point to have IP 192.168.1.2

Now set configuration in /etc/network/intefaces:

auto lo br0
iface lo inet loopback 

# Ethernet
iface eth0 inet manual

# Huawei 3G dongle
iface eth1 inet manual

allow-hotplug eth1

# Bridge
iface br0 inet dhcp
  bridge_ports eth0 eth1
  bridge_fd 0 # no forwarding delay

Configured DynDNS for my DNS provider Loopia according to these instructions. 

Works very nicely!

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