[CentOS] losing NFS connection

Sat Apr 30 19:11:15 UTC 2005
Kennedy Clark <hkclark at gmail.com>

> Just a thought but have you hard-coded speed and duplex all the way
> through? Don't trust auto-negotiation.

Sorry for the slow post -- trying to get caught up on my list reading
after a hectic week. :-)

My understanding from the IEEE 802.3u specs is that the key to the
"hard code vs auto-negotiate" debate boils down to: with the auto
setting of switch & NIC ports, SPEED can be DETECTED (based on the
speed of link pulses), DUPLEX must be actively NEGOTIATED.  IOW, if
one end has duplex hard coded, then the other end has nothing to
negotiate with and must DEFAULT TO HALF DUPLEX.

This results in 3 compatible combinations:

1) Leave both ends at auto.

2) If you are in a shop that is very meticulous about duplex settings
on both switches AND servers (hard to do in most large organizations
because different groups usually manage servers and switches), then
you can hard both ends to full duplex.

3) If you are in a shop where duplex misconfigurations are are common
(or left at the default) and going auto/auto everywhere is not
desirable, its best to hard-code to HALF duplex -- that way if the
other end is left at auto things still work.

So, while hard coding both ends to 100/Full provides maximum
throughput, forgetting to hard code one of the two ends will always
result in a duplex mismatch (and EXTREMELY low throughput).