I have a Dual-WAN router ER-6020. It is connected to my anemic CenturyLink DSL as a fail-over backup to my AT&T plan connecting via a Nighthawk M100. I work from home and need a reliable connection.

I have been sailing along for a long time with no problems. I was often seeing up to 100Mbps down using carrier aggregation. A few weeks ago, I started noticing a much slower connection. Multiple tests show it is now about 14Mbps down. I thought that maybe I was being throttled as I typically use >300GB in a month, but my billing period passed recently. Same speeds.

During the process of troubleshooting, I tethered the Nighthawk to my desktop directly (not going through the Dual-WAN router) and I can get close to 100Mbps again. I did this using both USB and Ethernet with the same result. Therefore, it appears the 6020 router is the problem. I did not change anything on the router and I can find nothing out of the ordinary on the router. It is entirely reproduce-able: tethered, speed is close to 100Mbps, through the router, is is around 14 Mbps.

I have run out of troubleshooting ideas. Can anyone think of something I haven't thought of to try to track this down?