From the gateway to my laptop, via cat 6 full internet speed. However if I go from the gateway to the TP-Link SG-105(un) to my laptop the speed literally tanks by about 85%. Its not the cable. Ive tried every cable, used, new, old, and nothing changes. Any suggestions? Thanks.
Modern switch including very cheap consumer ones do the function 100% in hardware. There is no firmware or software to load or even really running. There is very little that can go wrong. When they fail they tend to completely fail.
The switch should be able to run every port 1 gbit in and 1gbit out all at the same time so it can run 10gbit of traffic total not that there is a realistic condition where you can do that.
When you say it drops by 85% how do you get that number. If you see speeds on say speedtest around say 94mbps that generally means a cable is running at 100mbps.
I forget if the tplink switch has light that tell the port speed. You might be able to tell if it is running at 100mbps or 1gbit. The cable between the pc you can check on the pc side in the ethernet status, you have to look around microsoft like to move this around.
The cable between the router and the switch maybe the router has something that will tell the speed in a memu or maybe it has a light.
If both ports are actually running gigabit then it is going to be quite a mystery since a switch is a very simple device and you can't change anything anyway.
If you have a port at 100mbps it almost has to be a bad cable. Cables are really strange they can work on some devices and not others. This problem has gotten much worse in the last few years with all the fake cable being sold. Those flat cables are the worst offenders. They have wire that is too thin to meet the specs required for a cable to be a actual ethernet cable. You need pure copper wire with size 22-24 if you are buying a new cable. If you do not see this information look for another vendor.
Speed goes from 200mbps to around 15mbps. I have used dozens of cables... non of them have any issued when directly connected to the Tmobile gateway device. ONLY after pushing it through the switch. Ive tried 2 switches, the same model. Both acted the same. Is it the TMobile device or switch? I ended up connecting a very old router to the TMobile device, had a limit of 54mbps and ran a speed test connected to the router. Pegged at 54mbps. Using the same cables. So its not the cables and a router is not decreasing the speed.
Since you have used 2 switches and they both have the same issue it would point to the tmobile device even though I have no idea what. The tmobile device should not even be able to detect the switch they are completely transparent. The lan ports on the tmoble device are also a switch so from the router chip standpoint it is not even directly connected to the switch.
I doubt it but I would look for any settings on the tmobile router.
How old is your old router. Does it have gigabit lan ports. You could use it as a switch and you could also try plugging your linksys switch into the old router basically using it between the tplink and the switch