It seems to be quite consistently working for me. I've just switched to ADSL2+ on LLU, and due to the ADSL connection yo-yoing during the training phase, I plugged in my 3G dongle and confirmed that it does indeed fail-over reliably when ADSL disconnects occur, and switch back properly when the ADSL connection is re-established.

I'm not sure what would (or even should) happen if the fail-over occurs and TCP connections are made through the WAN2 interface, then the WAN1 interface comes back on-line. I can imagine an implementation that keeps the WAN2 interface active whilst it has active NAT sessions on its WAN2 interface. The fact that either or both WAN1 and/or WAN2 may be applying NAT means its not just a simple routing issue, as far as I can tell and abruptly switching between WAN interfaces would cause TCP connection failures. I guess if both WAN interfaces and all local hosts used public IPs with no NAT, then it would just be a simple routing issue and switching WANs would be a no-brainer.

In "WAN >> General Setup" I have both WAN1 and WAN2 set to "Auto Weight", with WAN1 "Always On" and WAN2 Active On Demand", and active on "WAN1 Fail".

Have you tried looking at the syslog stuff to see what is happening in the PPP session when the WAN2 fails to connect?

fnordianslip,

What speeds are you getting from the 3G modem (as I only seem to manage to get GPRS speeds)?

Also are you using a powered USB hub by any chance?

Thanks - j.

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jsturtridge,

No i'm not using a hub, powered or otherwise, although I am using a USB cable with a desktop base that came with an old wifi dongle, so I can get a bit more height on the 3G dongle and place it clear of obstructions.

I can't quote you any speeds, as I've not really tested in that respect and generally haven't run much traffic through it. I do get a blue light though with it plugged into the router, so at least I'm getting a 3G service.

If I do a speed test, I'll note the results here.

cheers,
fnord

fnordianslip,

Thanks for the speedy response. I'm just getting a green light ... so just at GPRS speeds. I might try relocating the dongle to see if there's any better coverage elsewhere.

It's great that this forum and everyone on it is so helpful.

Thanks again - J.

Having updated to firmware 3.3.2.1 (24 July 09) I now find that that the usb 3G stick is still seen on the 2820's on-line status screen BUT it shows a blank for the Signal field (used to show the % signal strength). I have the system set so that 3G is just on fail of the adsl.
Thought the 3G stick was no longer working, however on simulating a fail of adsl (pulling the phone line out!), the 3G connection came on :shock: and the Signal field then showed "45% (workable)"
So it seems that the new firmware still works BUT rather annoyingly does not show the signal strength unless there is actually a connection - the expression "2 steps forward, 1 step back" comes to mind! :twisted: