Slow ethernet Surf Soho Mk 3 when printer is on?

2020.10.20 UPDATE: I seem to have a slow ethernet connection when the printer is powered on. It’s connected via ethernet to the router in LAN-2; a Canon Image Class MF229dw. If the printer is powered on or in “save energy” snoozing mode, ethernet speed from router via LAN-1 to desktop-PC is around 30 Mbps. Unplugging the printer ethernet cable from LAN-2, or simply turning the printer off, results in ethernet speeds from router via LAN-1 to desktop-PC to rise to around 108 Mbps.

I setup the router with VLAN’s per Horowitz’s Router Security suggestions. Does anyone know why this would be the issue in the slowdown?

I am experiencing very slow ethernet download speeds w/re to my Surf Soho Mk3. I am aware the throughput is 120Mbps; my ISP is set to provide 150 Mbps. I am consistently getting only about 30 Mbps from an ethernet cord connecting LAN-1 to PC-desktop, while at the same time getting over 100Mbps via WiFi on such devices as my iPhone. I would like to figure out how to bring back my ethernet wired connection speed.

I am unable to say exactly when the problem arose. I do not remember having the problem back in July. I noticed the problem by September, and it may have been when I updated to Firmware 8.1.0 in September and moved to WPA-3 security. Resetting everything and even having my ISP do a maintenance “ping”/reset did not resolve the problem.

I tried the following “corrective” steps and at each turn the problem remained. I moved back to WPA-2 security (though I know that would not affect ethernet so much). I have now switched to Firmware 7.1.2 build 1387. I purchased and installed new ethernet cables to connect from modem to router and from router/LAN-1 to PC, just in case the problem was faulty ethernet cabling. I have also tried using LAN-2 to PC, just in case the problem was was a physical one with LAN-1 port. I have changed the MTU WAN value in settings to auto (they were custom before and I think set to 1400). I have changed the LAN Port 1 setting from trunk to access (all the remaining ports are access). I have ensured QoS is NOT enabled, and have disabled DSL/cable optimization. I still have the same issues.

I would note in passing that at least in some instances, the problem did seem to “correct” itself after swapping in and out various cables. At least last week, when I tested modem-PC and then went back to modem-router-PC, the ethernet speed seemed above 120Mbps, at least for a short while. Then the problem came back, usually within the hour (or so).

I realize some of the “corrective” steps were/are probably irrelevant. But at this point I’m at a loss. The ethernet cables seem good, and the modem-direct-to-PC via ethernet cable brings out the desired download speed of 120Mbps+. The problem seems to lie when I connect modem to my Pepwave Surf Soho Mk3 router, and then connect from LAN-1 to my desktop-PC.

What is it about my Surf Soho Mk3 that could cause modem-router-PC ethernet download speeds to be so low, while still providing decent Wifi speeds? Are there any settings I should attempt to adjust? Could I just have a unit that’s degraded?

Does anyone have any suggestions? Thanks.