Anything in statistics like crc and short frames indicating bad cable?
ethtool -S eth1
NIC statistics:
tx_packets: 6719840
rx_packets: 7950210
tx_errors: 1
rx_errors: 0
rx_missed: 909
align_errors: 0
tx_single_collisions: 0
tx_multi_collisions: 0
rx_unicast: 7950184
rx_broadcast: 0
rx_multicast: 26
tx_aborted: 0
tx_underrun: 0
I don't know what's normal for this read-out...
few underruns (missed) but nothing out of ordinary.
New cable installed... will have to let it run for a bit longer to be certain that solved the problem, but so far the speed has been stable at 800 Mbps. If it stays that way for another day or two, I might be tempted to say that was the problem. (At which point it'll immediately fail, so I'll probably have to make that report under a throw-away account to dodge Murphy's Law.)
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Not sure about the raspberries ethernet, but with luck it supports:
ethtool --cable-test devname
and/or
ethtool --cable-test-tdr devname
which might help debug a marginal cable, see
Note, this needs ethtool-full.
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It looks pretty sure it was the cable!
The scale on the graph is a little misleading (the X is per test, and I increased testing frequency when I started noticing more problems), but you can see the change on Nov 25 at 1800 where I replaced the cable.
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