Ethernet Adapter Stuck at 100MBPS

Question

_{Thursday, November 30, 2017 8:17 PM | 1 vote}

So I have a PC that is stuck at 100MBPS no matter what I do. I'll try to give a detailed explanation of what happened and what I have already done to troubleshoot the issue.

This PC is in a business setting on an active directory domain. I got a call about an issue with slow speeds, when I went to check the Ethernet adapter I realized that it was displaying a 100mbps connection despite our network being a gig. All other PC's are currently at a gig and most PC's are the exact same cookie cutter PC as this one.

The first thing I did was attempt to update drivers, no change.

Then I re-terminated the cable ends, no change.

The end of the day rolled around and when I came in the next day the ethernet card failed completely. So I put in a USB to Ethernet adapter to hold them off while I set up a replacement PC. (it needed to be upgraded to windows 10 anyway)

The odd thing was the even the gig compatible USB to Ethernet adapter ran at 100mbps.

I set them up with a new Windows 10 PC and all drivers up to date. They however were still stuck at 100mbps. At this point I determined that it was the cable. So I ran a new cable to the switch and plugged everything in. Still at 100mbps. I have Cat5e and Cat 6 cabling currently.

I re-terminated the ends one more time just in case but to no avail. Since we run to patch panels I thought I'd try to run it directly to the switch. Still 100mbps. I tried multiple ports and multiple switches and it just won't budge off 100mbps.

I went in to adapter properties and tried to force the speed to 1.0gbps full duplex. When I do that the PC doesn't even recognize a cable is plugged in.

At this point I have no other options and all the forums I have read regarding this issue point to old cabling, bad cabling, or driver issues. So I am hoping someone here has another option for me to try.

All replies (11)

_{Friday, December 1, 2017 12:35 AM}

What's the framing (duplex-setting)? It needs to be full duplex, auto-detect for Gbit to work. If you're set to half-duplex, forget it.

Jason

_{Friday, December 1, 2017 2:17 AM | 1 vote}

Your troubleshooting thread is ok.

When the network adapter is set to "Auto speed/Auto Duplex" in the properties, whether or not your network adapter really works on a Gigabit still depends on the hardware, network cable and the switch.

I would like to suggest that you confirm if all the hardware devices support the 1000bps speed, including network adapter and network cable.

One more thing, Half-duplex Ethernet has lower effective throughput.

Regards

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_{Friday, December 1, 2017 12:55 PM}

Hey guys, thanks for the replies. The only way the adapter actually connects is if its set to auto-negotiate or anything lower than 1gbps full-duplex. Setting it to 1gbps full-duplex and it doesn't even know that the cable is plugged in.

The cable is Cat6 so I know that supports 1gbps, the card I'm using are in multiple other PC's that have a gig connection, so I know the card supports it. The switches are 1gig switches as well.

_{Saturday, December 2, 2017 12:35 PM}

"Re-terminate cable ends?" You got out the crimpers and a fresh RJ45 connector and re-applied? Have you tried a known-good cable in place of the one experiencing issues? I am not questioning your cable-making skills. Any chance the switch-port is stuck on 100 while the others are not? Is there a different port that can be tried?

Jason

_{Monday, December 4, 2017 1:12 PM}

Yes, I did get out crimpers and fresh RJ45 ends. It's actually a very common thing for me to do. Our Maintenance crew does a lot of cable running when systems and equipment get moved or a new one is purchased. I am the one that terminates the end at the station and punches down the cable to the patch panel.

This cable runs about 150ft from the station to the switch so the only way to test with a known good cable would be to take the station out and bring it to the switch. However, as I said there are already two cables this has been tested on, and multiple ports on the switch.

Only thing I can do is bring the station to a known good cable, will take me some time.

_{Monday, December 4, 2017 10:23 PM}

To take the PC being the issue out of the equation, are you able to take the PC to a known gigabit PC and swap it over as a test.. If it is still at 100mb then its hardware/setting issue on the computer itself, if it is a gig then its a cabling problem. This might narrow it down a bit.

_{Sunday, June 17, 2018 11:48 PM}

What router do you have? Does it definitely have gigabit Ethernet? If it's just 'fast Ethernet' it will be 100mbps.

There's also an article claiming that certain powerline adapters only have 100mbps ethernet despite advertising higher speeds  

Assuming your router has gigabit Ethernet, if you plug the PC directly into it does this solve the issue? (ignoring the fact you don't want your PC next to the router for a moment).
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_{Monday, June 18, 2018 1:18 AM}

Hi.

Have you check that you're not beyond the 300ft? Another thing would be that the are not electricity crossing the cable.

The issue you're having is directly involved with hardware issue rather than software or drivers issue. As sson as you set the auto negotiate the speed, it will take the 1gb if the conditions are meet.

Richard Sabino

_{Monday, June 18, 2018 9:00 AM}

Sounds to me like bad cable...have you tried the problematic computer in other lan socket?

_{Wednesday, June 20, 2018 7:43 PM}

Was definitely a bad cable. Had a rash of older cables crapping out lately. Problems are all fixed by running new cable.

_{Tuesday, July 21, 2020 11:11 AM}

Thank you! Later I found out that my ethernet cable only supports 100Mbps, and wireless adapter 300Mbps. Now I see the problem.