I noticed the little light on my switch for the myth box is yellow instead of green indicating it's running at 100 Mbps instead of 1000.

My myth box is using the onboard GigE on a Gigabyte GA-M57SLI-S4. It's connected to the netgear switch via a 10' cat-6 patch, and has run at GigE speed for months. The rate has only changed in the last couple weeks.

ethtool confirms 100 Mbps on the myth side.

What logs should I be looking at to see why it is suddenly not using full speed?

Dumb tip, but it may work.

GigE needs all eight conductors in the cable to work. Perhaps one of them has a bad contact? If you have a cable tester, check it out. I've made a few cables myself, and have had a few fail from a bad cut or splice.

I haven't heard of this before. Do you have another patch cable? I think larry's idea is a good one. Beyond that, does anyone know how to force a mode?

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Retired KM user (R4 - R6.04); friend to LH users.

You can make various changes with ethtool. man ethtool reveals Scroll down to the -s option explanation for more.

I pulled the nice store-purchased Cat-6 patch cable, and replaced it with an old homemade Cat-5e cable that was sitting in a drawer. Bingo! the connection light went straight to green, confirming that this is a cable issue.

Now, should I be happy or pissed?

Happy, then pissed... that's usually the evolution of emotions for me in situations like that.

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Retired KM user (R4 - R6.04); friend to LH users.