jeffsf, maybe this is the root of all evil. The “router” upstream from the AR300M is a mobley hot spot. Just checked the setting on this and they are
but I also have DHCP enabled on the AR300M. I guess the wifi would still work on the AR300M this way but you would run into troubles with cascading the LAN out of the AR300M?
Looks like you’ve hit on it!
I would set the AR300M for:
Basically you’re turning it into an Ethernet-connected AP
I’m not sure what you mean by “cascading the LAN”, but you could change the switch config to assign the port presently used for WAN to the LAN bridge and have both ports on your LAN.
What I mean is that I need to have at least the one LAN port functional on the AR300M, so I can then in turn provide that LAN connection to another remote router being used as a wireless AP in my pole barn. The Mobley device that provides internet to the AR300M does not provide any hard ports.
And actually I am using the 3/4G connection over USB into the AR300M, not cable, but I don’t think that makes any difference.
It does make a big difference, as then the GL-AR300M needs to work as a router, not just an AP.
Would you sketch out your network to make things a bit clearer?
I actually USB tether a couple of different MiFi devices to my Mango and I’ve never had to turn off anything on the MiFi.
The fact that you’re getting a “good connection” via WiFi, to me means that the AR300M and the Mobley are working together fine.
Don’t have a MiFi with me at the moment but here’s a few screens that show what my Mango looks like if I USB tether my phone . I basically just plug in my phone, set to USB tethering, it shows up on the main GL.iNet interface and I click connect.
Here’s the LUCI interface screen (Network->Interfaces). You can see the bridge LAN/Wifi on 192.168.8.x and also the tethering on 192.168.42.x
With LAN cable plugged in I can see an active link and have internetz. (Network-> Switch)
Do your interfaces look similar? 
I can’t see anything wrong with your proposed setup, just the fact you can’t get an internet signal from the LAN port but can from the WiFi.
I’d be ignoring the TP-Link router until you can get a network connection to a notebook/desktop via the LAN port on the AR300M… Hardware or config? 
My next port of call would still be upgrade the firmware and reset all the settings and start from scratch or at minimum reset the router with the existing firmware and re setup !
One might ask, why not turn the WIFI server off on the Mobley hot spot, but if I do, I won’t be able to access the setting on it unless I factory reset and re-enable wifi as they only hard port on it is internet out over USB.
You also might ask why not just use WIFI on the Mobley exclusively, and the answer to that is it only support 5 clients.
The TP-link remote router is needed over ethernet connected to the LAN port of the AR300M as it is in a metal building through which no wireless will penetrate.
My mobley hot spot and the AR300M also work fine together right now as they are configured, but I cannot get the LAN port working on the AR300M. When I hook a laptop up to it I get nothing. Laptop sees nothing there.
Once you’ve got it setup right you should be able to turn off the WiFi on the Mobley as you should be able to get to 192.168.1.1 via a wifi or wired device on the AR300M subnet But first things first…
I have a screen that looks quite similar to the first one that you displayed, but I have no Network->Switch on my menu.
You need to get to the luci interface.
On firmware 3.x it’s Settings-Advanced but don’t know how on 2.x (can’t find doco). Try going to 192.168.8.1/cgi-bin/luci which may bring you to the luci screen. Just login with root and your normal password (sorry never used firmware 2. 0)
What happens if you click advanced settings top right?
(or as per the screen shot press the reset button for 10 seconds and hard reset so you can eliminate the config 
)
Ok could be the older version or a difference on the AR300m. Sorry but my initial recommendation still holds. Either reset on current firmware or upgrade and reset.
This will eliminate the config as the issue and point potentially to a hardware fault.
Just what exactly would you have me try once I reset the currently settings?
OK, thanks for the great illustration. I’ll look up the Mobley as I’m not familiar with how its providing IP connectivity over USB yet.
Configuration of the TP-Link device looks “right” and the GL-AR300M is probably right, depending on how the Mobley connects – just looks to be a question of getting the Mobley and its routing straightened out.
Edit:
The Mobley looks to be a ZTE-made, OBD-plug device that gets power over a USB adapter, or is it providing packet connectivity over USB?
Would you post the relevant sections of your /etc/config/network (or PM them, if you’re not comfortable posting them)?
Sadly, it’s a process of elimination to work out the issue:
Once you’ve upgraded and reset do the initial setup of the AR300m ( Language and password)
Plug in your modem and setup the tethering
Plug a device into the LAN port and see if you’ve got internetz
Connect to the WiFi and see if you’ve got internetz
If you haven’t on the LAN then there’s a high certainty that there’s a fault with the LAN port assuming cable and device are fine and also the Mobley are not an issue.
I’m basically just going through the steps I’d go through to diagnose .
Hopefully between that and Jeffsf’s suggestions
@jeffsf given how the mobley is normally powered via a car I’d assume it’s maybe 12V normally . Possible that the USB to Mobley adapter is drawing too much power for the ar300m to handle (assuming this is what @wacnstac is using) and stuffing the LAN port signalling?
" * May not be compatible with low output (mA) USB power sources like some smaller power banks or USB chargers"
The Mobley gets its power from an ODB II adapter not the USB (I am definitely providing it 12volts seperate from USB). It provides the connectivity over USB to the AR300M.
What device do you want the /etc/config/network stuff from and what is relevant? I hope if is from the AR300M as I don’t know if I can get that from the Mobley.
Yes, from the GL-AR300M – how the interface to the Mobley is defined, especially the driver, protocols, and addressing involved.
My current thought is that you’ll need to have the GL-AR300M’s WAN be a client of the Mobley’s DHCP and use NAT, as I think I read that there is a five-device limit on the Mobley.
There is definitely a 5 device limit on the number of wireless devices that you can hang off the Mobley but what I don’t know is if this extends to the Mobley’s DHCP handing out IP addresses.
I will get you the /etc/config/network from the AR300M, but don’t know how much more information I can get you on the Mobley.
In the mean time, consider setting up the WAN interface as DHCP with however you’re connecting to the Mobly. Since it’s handing out on 192.168.1.1/24 and the GL-AR300M is handing out on 192.168.8.1/24, there shouldn’t be a conflict. “Double NAT” isn’t great, but if your looking for general Internet access, it should work well enough for you. (Likely no way to get rid of double NAT without being subject to the five-device limit.)
