TP-LINK 3420 + OpenWRT + Huawei E398 = 3G WiFi AP

Update on 2012-03-17: the latest firmware supports this out of the box, no need for manual modeswitching and such.

Here is the path that I followed to get my wireless access point up and running. So far I havn't got more throughput than ~7Mbit and this is probably due to the serial interface, there is supposedly a network interface available on the E398 but that is another story.

Edit: when running a throughput test on my laptop I got ~15Mbit compared to the lower number that I recieved on my IPad. Which means I won't bother to tune any parameters performance wise.

1. Install OpenWRT on the router, I used the upgrade function which works great.
2. Use telnet to log in to the router, set a root password. Disable firewall to be able to log in through WAN port on router (as you need internet access from the router as well as administration access through SSH from your computer).
   /etc/init.d/firewall stop
/etc/init.d/firewall disable
3. Make sure the router has internet access, I used internet sharing on my internet connected laptop and the WAN port of the router.
4. Find the IP address of the router (which in my case is distributed from my laptop), I used PowerShell.
   1..255 | foreach-object { (new-object System.Net.Networkinformation.Ping).Send("192.168.137.$_", 10) } | where-object { $_.Status -eq "Success" } | select $_.Address.Address
5. Connect to the router using Putty or some other SSH client. Install the following packages through the opkg tool; comgt (3g scripts), usb-modeswitch (used to switch the mode on the modem from storage to modem), kmod-usb-serial (to be able to use the modem as a serial device).
   opkg install comgt
opkg install usb-modeswitch
opkg install kmod-usb-serial
6. Add the usb-modeswitch command to be run on startup through /etc/rc.local. Add the following line:
   usb_modeswitch -v 12d1 -p 1505 -M "55534243123456780000000000000011062000000100000000000000000000"
7. Make sure the device that pops up on modeswitch is recognized as a serial device, add the following line to /etc/modules.d/60-usb-serial
   usbserial vendor=0x12d1 product=0x1506
8. Last but not least create an interface configuration for this new connection by adding the following to /etc/config/network
   

   config interface wan
           option ifname   'ppp0'
           option proto    '3g'
           option device   '/dev/ttyUSB0'
           option apn      '4g.tele2.se'
           option pincode  0000
           option auto     1

9. If you wan't this connection to start on boot the auto flag is NOT enough, you can work arround this bug by adding the following script /etc/init.d/network3g
   

   #!/bin/sh /etc/rc.common
   
   START=41
   STOP=91
   
   start()
   {
       include /lib/network
       scan_interfaces
       for ifc in $interfaces; do
           config_get ifproto "$ifc" proto
           config_get ifauto "$ifc" auto
           [ "$ifproto" = "3g" ] && {
           case "$ifauto" in
                   1|on|enabled) ifup $ifc;;
           esac
           }
       done 
   }
   
   stop()
   {
       include /lib/network
       scan_interfaces
       for ifc in $interfaces; do
           config_get ifproto "$ifc" proto
           [ "$ifproto" = "3g" ] && {
               ifdown $ifc 
           }
       done 
   }

10. Then configure WIFI etc. Remember to enable the firewall...

I rather like this little setup. The router cost me about 30€ and the mobile plan, including modem, is 17€. Big thanks goes to:

• Daniel Holm - blog in swedish
• OpenWrt - and the people behind it