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CentOS 6 router/firewall seems to be throttling throughput

After much troubleshooting the problem turned out to be a hardware fault with one of the network adapters. For unknown reasons the adapter refused to "see" the peer's advertising of 1Gb speed, connecting at 100Mbps. Even forcing it to 1Gb and autoneg-off with ethtool had no effect.

I replaced the adapter with a newer one based on the same chipset (R8169) and the problem disappeared, now connecting at 1Gbps as expected.

My first reaction is to delete the question, but I can write an answer that explains the resolution as a reminder to future readers to make sure the hardware is OK before blaming the software.

I will defer to the community's wishes on this.

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The second option is more useful. Sometimes "Replace the hardware" is the correct answer. To make it even more helpful, add information that lead you to test this angle.

  • Thanks, answer is written. I'll accept it in a day or two. – Ex Umbris Jan 7 '17 at 21:39
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    @ExUmbris I'd already upvoted your question. Now I've gone back to upvote your answer as well. Would that every fairly-low-rep user put this much thought into their questions, and the maintenance thereof. – MadHatter supports Monica Jan 8 '17 at 7:43
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    Thanks for the kind words. I hope the question and answer help someone in the future (which is the whole point of Stack Exchange:-) – Ex Umbris Jan 8 '17 at 7:48
  • After working in cloud infrastructure, it became about 50/50 whether I'd check hardware or software logs first - usually leaning whichever way I thought had better diagnostics in the problematic area. Document as much as you can about the software symptoms of the hardware fault - someday someone will thank you. – Matthew Wetmore Nov 8 at 20:33

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