08-30-2016, 01:57 AM
(08-30-2016, 12:12 AM)MarkHaysHarris777 Wrote: hi, good question... with the unmodified cable I can use the ethtool to set speed 1000 duplex full; but, it doesn't work at all ! With the modified cable the link comes up 100 /full, which is why its working so well; if I use the ethtool to set speed 1000 duplex full it DOES go into 1000 full for about 20 seconds and then the link goes down (this is reproducible). If I bring the linke back up manuall without reboot [ ifconfig eth0 up ] the link comes up 100 /full.
The temporary good news here is that while we're trying to figure out what needs to be done to the card, the 100 link comes up automatically now without intervention so that (in my case only) the GbE switch is now useful. The machines (2) that can use it do, and the one that cannot use it comes up 100 by default... so my wired GbE network just had an order of magnitude improvement !
Interesting... certainly once again reinforces that the issue is GbE auto-negotiation related. The behaviour of ethtool forcing GbE is understandable with the modified cable, since you basically disabled GbE capability by removing the two normally unused pairs, and after some thinking, the RTL8211 realises something is wrong... tries again, and establishes the link at 100Mb. However, I certainly won't be recommending this fix to anyone as it is a waste of a perfectly good GbE capable cable. If adding 'ethtool -s eth0 speed 100 duplex full' to/etc/rc.local is all that is needed, I would consider that as the best compromise until (if) a solution is found. However, it is interesting as a data collection point, as it did force the auto-negotiation to not consider GbE, and then allowed things to work.