What I am trying to achieve is two have two uplinks out to the internet from the Netbox blue so if the primary drops it will fail over to the secondary.
One uplink (Primary) is an ADSL 2 service which a modem in bridge mode to the Netbox and the 2nd uplink goes out into a TP-Link TL-MR3420 (Configured only for 4G) which has a Telstra 4G Wireless Stick connected into it.
What I am trying to achieve is if at any chance the main link fails we can fall back on the 4G connection. What is currently happening is that the 4G connection Secondary uplink (4G Stick into the TPlink) stays connected and online as I can see this under Administration > Link Status. IT does not drop out. I am also able to ping Google.com through this interface with the diagnostics tools inside the netbox blue.
As soon as I change the default route to go out the 4G uplink the 4G uplink goes down after 6 minutes or so. I have looked at Traffic reports on the Netbox blue and on an average a day the site does not download/upload more than 1GB between all 6 machines onsite. This eliminates the link is becoming saturated.
I have replaced the TP-Link router and also the 4G dongle and sim in the dongle and this has made no difference.
Can someone help shed some light on this? What i am thinking is that Netbox is performing NAT and so is the TP-Link modem so we are double nating which is not good. I have also found out with the Telstra 4g Sticks that alot of the IP address they handout are Private IP addresses which then adds another process of natting to go out to the internet. I hope this makes sense.