Figure out where is the culprit first. Buy a cheap cat 6 cable and test. If the cat 6 cable works, then the problem is in that cat 5e cable. If cat 6 cable also cannot work, then the problem lies in your hardware (modem/router/ethernet card/PC setting).

This post has been edited by Max2006: Aug 1 2018, 02:00 PM

Erm actually i slept early yesterday and now i just starting to fix it 😁 thx anywhere for ur help

if there is any devices link to LAN connected with Force to 1Gbps, it will defaulted no connections.
Means the devices is the culprit

Take the path of least resistance, check the cable first. Use another one and see what happens.

I used the cat5e from my dlink router box and it achieved 1 gbps but the cable is very short just about 1 meter

This post has been edited by ootik123: Aug 1 2018, 03:05 PM

Realtek is known to be picky with cables quality/length and gigabit. Try the problem cable with another PC/Laptop that doesn't use a Realtek LAN if you have any. If that works at gigabit, then you have to hunt for a different cable that works with your Realtek LAN.

Happened to me when I decide to wire my house with Gigabit, all non Realtek LAN (Intel/Qualcomm/KillerLAN) connect to my router at Gigabit. The two PC with Realtek LAN connect only at 100Mbps. All used the exact same cable

This post has been edited by thewan: Aug 1 2018, 03:17 PM

Maybe the quality of thr cable,i tear it off any the cable just like silver fiber

Go google how to change settings inside your network driver to gigabit, that's why you get 100Mbps instead of 1000Mbps.

I think more or less confirms that it's a cable problem. 1m, 5m, 10m shouldn't make any difference even for cheap cables. It could be a reason other than the quality, maybe the heads were crimped wrongly, or there's a break or a short somewhere along the cable.

Where did that problematic cable come from?

This post has been edited by soonwai: Aug 1 2018, 03:52 PM

Problem solved if i used another 1meter cat5e from dlink stock router . Im now planning to buy a new cable cause sometime there is some ping spike from this low quality cable . What should i buy cat 6 or cat 7 ? Length between router to pc is about 5 meter

Solved it is the cable causing it

try disable network card. then re enable.

try the same cable on different laptop/PC capable of 1gb connection.

try other cable.

another thing, what is length of the lan cable? signal degradation (attenuation) start with longer cable..cat5 supports up to 280 feet...

most of the time it is a cable. A lot of devices dont show this but some devices show stats and if there are errors it will lower the speed.

Not just cable but interference as well can do that. Because its dlink i would not trust it.

Realtek is not picky on cable quality, a lot of chipsets have their stuff, realtek has the least hardware/footprint and that is their advantage, i find realtek to be great for low latency networks where throughput isnt a concern.

Erm yes it is. You just haven't found a cable that affects your realtek yet. I have referred my problem to snb forums and the replies there all say the same thing, Realtek doesn't like the cable I am using. My entire house is now Realtek free as I've upgraded those two older PCs and the entire house is now gigagbit. I'm not gonna buy new wires and rewire the whole house again when other non Realtek LANs works fine. Before you ask yes I tested transfer speeds between the non Realtek LANs, both normal network copy/paste and iperf and they show gigabit speeds, up to ~90MBps. So there is nothing wrong with my cables.

My conclusion is, if you only have one problem device/cable, then try a different cable. But in my case I have already wired the entire house, and and every other device works fine (yes even the connection between my router and my unifi modem is gigabit) so I didn't change the cable. I just made sure the next time I replace/upgrade PCs I don't go for Realteks. I have nothing against them. Its just in my case, which admittedly while rare it does happen based on my research, I decided to just move away from Realtek so that I have less headache to deal with.

This post has been edited by thewan: Aug 2 2018, 12:21 PM

mind sharing said favorite gigaLAN chipset/s here?

actually i find that my router's qualcomm chipset or the switch chip is less tolerant and a laptop's marvell NIC to drop down to 100Mb/s before my PC's realtek NIC does so.

That's interesting. What brand cables are you using? Strange that a network chipset can be affected by the brand of cables. What affects it? Aluminium, copper, resistance, impedance, conductance?

My 2 main computers are Realteks; Zotac Z77ITX, cheapo USB3 GBe for my MacBook. The MacBook is connected to a router using a Mediatek switch chip and the PC is connected to one using a Artheros switch chip.

This just made me realised that I don't know the brand of cables used in my house. Or I had forgotten. I must have specified something to the contractor. Must go check.

brand does not matter, the quality does. A lot of cables call themselves cat5e when they hare only cat5a, and so on. A cat 7 cable was found to be cat5e. If most people use gigabit, they wont realise the difference until they start getting errors and interference.

Yes but it might be difficult for thewan to answer if I asked “What quality cables are you using?”