r/techsupport • u/Synfl • 5d ago

Open | Hardware Networking / Switch speed issues : Switch randomly dropping from 2.5gbs to 100mbs.

I am attempting to use TP-Link TL-SG105S-M2 to divide my singular Ethernet port in my home office to just 3 devices. Plugging from the wall directly to my device I receive 5000mbs Up&Down. Into the switch->1st PC 2.5gbs. However randomly the switch will disconnect and reconnect shortly after and only allow 100mbs. Upon resetting the switch by unplugging power for 10~ seconds its fine only to do the same shortly later. I am using different Ethernet cables and getting no difference in speed unless i use a less capable cat cable.

Also when attempting to use a connection for a wifi booster (TP-Link RE515X AX1500 limited to 1gbs) that has an Ethernet connection, it drastically limits the speeds my PC gets down to a maximum of 300mbs which shortly drops to 90-100mbs later.

I bought brand new cables from uGreen and have no issues if plugged from the wall directly to PC.

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u/meanwhenhungry 5d ago edited 5d ago

Bad cable and or too long, or you got cat7+ Ethernet that breaks with any slight bend.

For context, super long run from router to switch. Then a run to another switch.

Switch one is fine, anything on switch 2 would drop to 100 every once in a while often until the switch power cycles.

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u/blud_13 5d ago

Falling to exactly 100 and not 1000 is the the BIG sign. 2.5G needs all four pairs, 100 only needs two, so a marginal pair or a bad contact at one jack renegotiates you straight past gigabit. Since it comes back on a power cycle and then dies again, Id look at the wall to switch part before the switch to PC part.

Swap ONLY the wall to switch cable, reseat both ends, then leave it alone and see if the pattern changes. Different wall port too if you have one...

Heat is the other one. Those fanless multi gig boxes get genuinely hot and seen them start flapping links once theyre warmed up. Put your hand on it right when it drops.

The RE515X is a 1G device so that part caps at gigabit no matter what, that's expected. But 300 falling to 90 is the same flapping showing up twice.

Also, the wall gives you 5G and that switch tops out at 2.5G, so youre giving up half your line just by going through it.

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u/JasonHofmann 5d ago

^^^ all this

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u/the_gamer_guy56 5d ago

Blow into the ports like its an old cartridge game. I've had dust and stuff build up in there and cause links to auto-negotiate down. 2.5Gbit is more sensitive to signal issues on the line than 1gbit. Also, make sure to never use those flat low profile cables. The effects of the twisted pair is reduced in those and the crosstalk/interference is atrocious. For 2.5Gbit I could never get those to work reliably. On 1Gbit they were hit or miss. I replace all my flat ones with proper cables and its been doing 2.5Gbit for years with zero link downs.

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u/SomeEngineer999 5d ago

Is the PC to switch connection dropping to 100 or the one from the switch to the PC? If it is the PC one, try disabling energy efficient ethernet (and can try disabling other power saving settings on the PC's NIC too).

Make sure the PC is set to auto/auto for speed and duplex.

If none of that fixes it, I'd RMA the switch.

If it is the link between the switch and your router (or the next switch) then it could be a cabling problem. All it takes is one pin/wire with a less than perfect connection to cap you at 100M link speed (or around 95M max throughput).