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Question: 2013 iMac ONLY negotiates 100 Mbps

I have a Late 2013 iMac running High Sierra 10.13.2 that will only negotiate 100 Mbps on the built in ethernet port. It works fine at 100 Mbps. I would use the thunderbolt adapter, but I am using both ports for additional monitors.

Below are my completed trouble shooting steps.

1. Cable. I connected the cable to the same switch port with a thunderbolt adapter and it negotiated 1000 Mbps on my iMac.

2. Switch. I used the same port, cable, and thunderbolt adapter on my MacBook Pro and it too negotiated 1000 Mbps.

Is there any remedy to this nightmare?

iMac, macOS High Sierra (10.13.2)

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Dec 11, 2017 11:00 AM in response to dav3nator In response to dav3nator

Update: My iMac has both 3.28.1 and 3.28.2, so I logged in with my admin account and launched terminal and ran the command "sudo softwareupdate --background," then restarted. This did not appear to do anything. Up until Apple released the update that "broke everyones ethernet port," my port was operating at 1000 Mbps (Gigabit). Now it's working, HOWEVER it will only negotiate 100 Mbps (Fast Ethernet). If I manually set the speed to 1000 Mbps it drops the connection.

Dec 11, 2017 11:00 AM

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Question: 2013 iMac ONLY negotiates 100 Mbps