Cellular Phone/USB Modem as WAN connection

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[edit] Main Guide

USB Tethering with an Android phone, or using a USB Modem, on your DD-WRT-enabled router.

[edit] USB Phone Tethering [Attach an android-based phone via USB to a router]

NOTE: DD-WRT builds 55779 and newer include Android tethering as an option by default on routers that include the kernel modules and have a USB port.
NOTE: This guide is problematic as it does not add the route gateway for the WAN properly on builds after 51140. There are workarounds.

Already tethered your phone to your computer via USB (or wifi) and now you want to move up to having a full router?

Testing w/ Phone: 1st tested with a Verizon Visible R2 (5/2mbs) on 5/20, but then upgraded to a Pixel 2 w/PixelExperience 6/21 [with Band 66 and Carrier Aggregation support], and then tested with a Pixel 3a G020G (rootable) 11/21. Service: Visible LTE-only pre-pay [bandwidth on the VR2 and other non-Band 66, Non-CA phones is typically 5/2Mbs, but with the better Pixels, it is typically 15Mbps down, 15+mbps up, on AWS Band 66+CA. There is no data maximum per month after which your data rate becomes unusable (e.g. 50GB 'unlimited' limit on Tmobile Pre-pay)]
Router: 1st: Linksys EA6400 running DD-WRT v3.0-r37012 std (2018/09/21) and also works with r42819 (2020/03/30) [fully tested!].

[edit] Requirements:

1. Make sure the necessary modules exist on your build. This is very important. Some router builds are simply missing the modules, and it is beyond the scope of this guide or the ordinary user to build their own versions of the missing modules: We will go through the steps to check for this. This guide assumes that the build you downloaded and flashed of DD-WRT, has the modules cdc_ether.ko and rndis_host.ko, which are not present on some builds (regardless of build size) but required for USB tethering. If they do not exist on your build, you may need either: a larger version of DD-WRT that includes them, or to reflash over to OpenWRT [However OpenWRT has limited Broadcom support!]. These are -very small- modules (8kb) but are not included on some larger builds for some routers.

2. Reset your router: This assumes you have saved your existing Router settings first, before resetting your router to test these USB Tethering settings. If you've done some custom config since flashing your router, and you want to keep it, first: back up your settings, then reset the router, and test this out. If you can get it working from a reset router, then if it does not work with your custom settings, you'll have to figure out what additional steps you need to do that are beyond the scope of this article.

[edit] Steps:

  1. Router: Main configuration page: leave WAN on Automatic DHCP. Set the MTU manually between 1200-1428 (max) [1]. Set your timezone. Save & Apply.
  2. Phone: connect it to router's USB port with a USB cable you've already used for successful tethering with your laptop.
  3. Phone: Turn on your phone's Developer Options: [Click 'Build Number' in 'About Phone', 7 times in rapid succession]
  4. Phone: Search for 'Default USB Configuration' in 'Developer Options'. Set it to 'USB Tethering'
  5. Phone: Permanently turn off your screen lock (PIN or pattern etc). The phone must be unlocked for USB Tethering to turn on automatically when the router is booting-up, with the phone plugged in & powered-up from the Router USB port. A locked phone will not tether when the router's USB interface turns on.
  6. Router: Services, USB: Enable 'Core USB Support'. Apply.
  7. Phone: USB Tethering should now turn on automatically. Check to make sure this is happening.
    You can press Cancel or simply ignore the pop-up that appears asking what USB connection mode the phone should use. It will have USB tethering turned-on either way at this point.
  8. Router: Telnet into the router. Run the following commands:
    Press Enter after each command. insmod commands will insert modules quietly, and not report success.
  9. ls -a /lib/modules/$(uname -r) check for presence of usbnet.ko, cdc_ether.ko, and rndis_host.ko
    (you do NOT need to be in the modules directory to execute the following)
  10. insmod usbnet.ko
  11. insmod cdc_ether.ko
  12. insmod rndis_host.ko
    Use the command 'lsmod' to verify the modules usbnet, cdc_ether and rndis_host are running.
  13. ifconfig usb0 up
  14. udhcpc -i usb0
    You should be able to 'ping google.com' now from within the telnet interface, but not yet on any connected client devices. Noobs: CTRL-C to stop pinging.
  15. iptables -t nat -A POSTROUTING -o usb0 -j MASQUERADE
  16. iptables -A FORWARD -i br0 -j ACCEPT
    You should now be able to ping google.com from any client devices.
  17. MSS Clamping: the following corrects potential MTU issues when connecting a phone to a router. It is a workaround for upstream provider issues. A common symptom is, Android devices connect to WiFi, but then periodically report 'No internet'.
    iptables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
  18. If you are trying to hide tethering:
    iptables -t mangle -I POSTROUTING -o $(get_wanface) -j TTL --ttl-set 65
    iptables -t mangle -I PREROUTING -i $(get_wanface) -j TTL --ttl-set 65
    The actual value of '65' varies with the upstream provider.
  19. Fully test your apps, websites and other services on all your connected clients.
    Everything should be working at this point.
  20. To make the router configure automatically on bootup, automate the above process by adding the following lines to the Startup script:
  21. Go to the tab Administration, Commands.
  22. Paste: [these are the commands you used above]
    insmod usbnet.ko
    insmod cdc_ether.ko
    insmod rndis_host.ko
    ifconfig usb0 up
    udhcpc -i usb0
    sleep 5
  23. Click 'Save Startup'.
  24. Paste:
    iptables -t nat -A POSTROUTING -o usb0 -j MASQUERADE
    iptables -A FORWARD -i br0 -j ACCEPT
    iptables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
  25. Click 'Save Firewall'.
  26. Click on (Administration) Management. Click 'Save'. Then 'Reboot Router'.
  27. You may have to reboot the router if you make configuration changes.

Again, everything should be working at this point. You are finished with this guide. Thank you!

Credits: Users sydlexia and shenoyh on the forums for the source information.

See link: https://forum.dd-wrt.com/phpBB2/viewtopic.php?p=1128616#1128616

[edit] USB Modem [Use dongle that contains a SIM]

There are newer methods, integrated into the firmware than the previous version of this wiki. The relevant threads: K26 NEWD-2 Mega/Big builds starting with 14414 now have the 3G/UTMS WAN connection option built into the firmware.

See the following thread for more information:


See also http://www.dd-wrt.com/wiki/index.php/Mobile_Broadband for a list of directly supported device in K26 and K3.x builds.