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Fraxie Author

Level 1

26 points

1Gbps ethernet speed changed to 100Mbps

I have 1Gbps fiber internet. It's been working great. After months and months, I finally updated MacOS from Sierra to High Sierra.

Nothing changed with the hardware. Nobody bumped the desk, the iMac, the network switch, or anything. Upon finishing the update, the network will not connect faster than 100Mbps.

The system is a Late 2013 27-inch iMac. It's has a perfectly functional 1Gbps ethernet for years. I update the OS and boom, the network is stuck at 100Mbps.

Interesting thing to note, even Windows 10 running in BootCamp failed to connect faster than 100Mbps... but only AFTER updating to macOS High Sierra. It never failed to connect at 1Gbps before the macOS update.

I tried resetting SMC.

I tried resetting NVRAM.

I booted into and out of Safe Mode.

I completely wiped the system clean and installed a fresh macOS install.

Nothing worked.

I even plugged a USB 3.0 1Gbps ethernet adapter into the system, and it connects at 100Mbps.

I have a Windows 10 PC right next to this, and it works at 1Gbps no problems. The USB ethernet connects at 1Gbps no problem. I swapped the ethernet cords just in-case. The iMac still connects at 100Mbps and the Windows still connects at 1Gbps both internally and using USB.

If I wasn't already bald, I'd be pulling my hair out! Can someone please help me?

Thanks.

iMac, macOS High Sierra (10.13.6), null

Posted on Aug 21, 2018 11:04 PM

Top-ranking reply

Cirigliano

Level 1

4 points

Posted on Jan 4, 2019 5:55 PM

Hi All,

I had this exact issue with my MBP mid 2015. Ethernet connection via Apple's thunderbolt adapter would only connect at 100Mbs. bringing my internet speeds to a miserable 80Mbs when I get 275Mbs on my 5G wifi connection. If I would switch the adapter hardware settings to manual and set it to 1000baseT it wouldn't even connect. After having my ISP come here and look at my router, all checked out well with them. So no issues with the router. Now I call Apple and get to top level tech and we try all sorts of things and nothing is helping.

What I noticed while waiting on hold, I pulled out the ethernet cable from the adapter and noticed that one of the gold pins in the adapter was slightly bent down (for me it was the 4th pin from the left). It wasn't bent very much but I could see a difference from the other pins. So I grabbed a sewing needle and was able to gently get the needle under the one pins and carefully bent it back into place and BOOM! It worked at 1000baseT again.

In short, check the pins in your adapter see if any of them look out of place even just a little from the other pins. Try to bend them back with a needle but be careful they can break very easily. If it breaks, you will have to purchase another adapter.

This more than likely happened by being thrown into my backpack with other adapters and pens etc. Im guessing the adapter and a pen got into a fight and the adapter survived with minor injuries this time. I will keep them separated now on since they can't get along together.

Apple did a great job trying to troubleshoot and were top class even though it ended up being an adapter issue.

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25 replies

Feb 26, 2019 7:06 AM in response to Fraxie

I got similar issue, my iMac mid 2017 shows cable unplugged. However, when change hardware setting to automatic, it's connected but in 10baseT/Full duplex only. Other setting will be disconnected with cable unplugged message. After SMC/NVRAM, reinstall o/s, install older version o/s on external hard disk still in vain. Contacted Apple support online also no help at all. So decided to use USB-C to Giga Ethernet instead of built-in network port.

If anyone have same issue, pls post here, to let apple solve it asap.

Thanks

Feb 26, 2019 9:03 AM in response to JMBIELSKI

My imac always direct connect to the router using amp cat6 cable. And the setup never changed /moved since i bought it on aug17. I also checked the pins in the ethernet port, all are nice and shinny. when using usb-c to ethernet adapter with attach to same cable and same router port. It can reach 1000baseT. So rule out possibilities on router and cable. The issue is coming from my imac.

Aug 22, 2018 2:30 AM in response to Fraxie

(ignore)

rccharles

Level 6

12,969 points

Aug 22, 2018 8:39 PM in response to Fraxie

pita. You could try loading whatever macOS you had before and see what you get.

Aug 23, 2018 10:38 PM in response to Fraxie

Glad to know the Thunderbolt adapter works and that eventually you have full Ethernet speed back. 🙂

rccharles

Level 6

12,969 points

Aug 24, 2018 9:10 AM in response to Fraxie

Thanks for reporting back.

Very strange.

Aug 28, 2018 3:17 AM in response to Fraxie

I'm having the exact same issue. AT&T says it's my Mac. Apple says it's ISP. This thread is helpful. Hopefully, there's a solution soon.

vokey

Level 1

4 points

Dec 10, 2018 11:31 AM in response to VikingOSX

I had this same problem....

then realized that WiFi was on at the same time.....it was overriding my GB Ethernet connection

I turned out WiFi....and problem solved

BDAqua

Level 10

245,375 points

Jan 4, 2019 6:06 PM in response to Cirigliano

Nice tip. :)

Jan 20, 2019 9:38 PM in response to kriskoeller

I've noticed the same issue on my late 2015 iMac possibly since installing Mojave. Did you ever resolve this and get back to full speed? My hardware has been stuck at 100baseT.

1Gbps ethernet speed changed to 100Mbps