[aetsch-baetsch]

Hello everyone!

I've a WRT1900AC Router with DD-WRT v3.0-r36247 and all things I need are running very well.

Currently my provider renew his cables and so we have connection problems to the internet sometimes. So I bought a USB modem and changed the WAN setup to "Mobile Boardband" with the correct settings at dd-wrt webinterface. So far, so good. Everything works as it should. The only problem is, that the provider of the USB modem is very expensive (pay per MB).

Now I want, that the router only switch to the USB modem if my primary WAN (Automatic Configuration - DHCP) is broken. A failover I mean.
If primary WAN come up again, the router should switch back to it.

So I started to read the wikis like:

Dual WAN with failover
Dual WAN with one as standby backup
Cellular Phone/USB Modem as WAN connection

and also threads like https://forum.dd-wrt.com/phpBB2/viewtopic.php?p=870232

Unfortunately I don't get it to work. One of my problems is that I don't find the correct interface for the USB modem. It isn't usb0, eth3, ...
How does it work? I really want to know it.

So is anyone here who can help me please?

Thanks!

[pbphoto]

It's not a usb modem but maybe something to consider. On my home network, I use a Netgear LB2120 ethernet modem in between my 3200ACM and my ISP's router. If it can't ping a well known IP address, 8.8.8.8 for example, it will automatically switch over to the cellular backup service. It takes less than 30 seconds to failover, and even less time to fail back.

In my LB2120, I use an AT&T sim card with a basic $27 month for 10GB data plan. It's plugged into the WAN port on my 3200ACM and it's static IP is the wan gateway for my 3200ACM. On the other side, my ISP's router is configured to passthru all incoming IP traffic to the LB2120's mac address.

[aetsch-baetsch]

Thanks for your answer, but I would like to get it to work with my USB modem.

I found out, that ppp0 is the interface what I've been looking for.

And here is the next problem:
When I try to "start" it with