Macbook Pro does not see Fast Ethernet but works fine with Gigabit Ethernet

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Macbook Pro does not see Fast Ethernet but works fine with Gigabit Ethernet

Hi to everybody,

It is some time I have a problem connecting my unibody Macbook Pro (late 2008) to the ethernet cables in my office. There are 16 wall jacks in the lab, of which 13 are Fast Ethernet (100 Mbit/s) and 3 are Gigabit Ethernet. No matter what I do, if I connect to the 100 Mbit/s jacks, my Macbook does not see the connection and keeps saying "Cable unplugged". If I switch to a Gigabit jack, then a connection is quickly established.

I have spent one whole afternoon debugging. Here is what I did:

My computer dual boots Mac OS X and Linux. No matter which operating system I use, the problem is the same.
Using different Cat.5 cables does not change the situation (I tried three of them.)
All the 13 Fast Ethernet jacks do not work.
All the 3 Gigabit jacks work smoothly.

What puzzles me is that my computer happly uses the newest technology (Gigabit ethernet) but has problems with the oldest one. Has somebody else experienced the same problem?

MacBook Pro, Mac OS X (10.7.5), Unibody MacBook Pro (late 2008)

Posted on Dec 20, 2013 10:25 PM

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Answer 1

ziotom78 Author

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Jan 7, 2014 6:09 AM in response to ziotom78

After a lot of struggle, I discovered that other people had this very issue as well. It seems that the cause is a faulty Realtek chip used in the ethernet cards of some MacBooks and other brands. There is apparently no way to fix this: I solved my problems by buying a Gigabit Ethernet switch which I connected to the Fast Ethernet wall jack. (Another option might be to use a Ethernet-to-USB adapter - but I did not try this as I have no adapter of this kind.)

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