[Bioclusters] Xserve going full duplex

[Donald Becker]

On Fri, 8 Aug 2003, Chris Dagdigian wrote:

> Ruotti, Victor wrote:
> > Chris:
> > We have two xserves here at the Medical College and the problem is that the
> > Ethernet cards will not go to full-duplex. We have tried to use the ifconfig
> > utility but it don't seem to work. Have you experienced the same problem?

In general you should not use 'ifconfig' to force the physical
parameters or media type.  Some Linux distributions put this in
'ifconfig', but it's not portable or cross-compatible.

> I think this was a recent thread here as well as on biodarwin. First 
> suggestion is to look at the switch you are connecting to -- I've often 
> had duplex negotiation failure problems with Cisco, Foundry and Dell 
> Powerconnect switches when working on linux systems.

Presumably not with the current version of their switches (and rarely
with Foundry).

Pointing to Linux in general is also a little misleading: we throughly
test drivers before release (although modified drivers are rarely tested).

> You should first try to adjust your switch to disable negotiation and 
> force the appropriate ports to be full-duplex. That may solve your probelm.

That is a very bad solution.  If you must must disable autonegotiation
because of flawed hardware, disable the broken end and allow the link to
use half duplex.

Auto-negotiation is reliable, and failure is always because of flawed
hardware.  In the past there were several switch vendors that didn't
want to acknowledge problems with what they were shipping, and therefore
implied that auto-negotiation was flawed as a concept.  Modern products
almost universally implement it correctly, and there is now a quiet
restatement of recommended practices.
  http://www.cisco.com/warp/public/473/46.html

A quick background on autonegotiation is available at
  http://scyld.com/expert/NWay.html


Bottom line: Auto-negotiation works.  If you turn it off because of
broken switches, never set the port forced-full-duplex mode.

-- 
Donald Becker				becker@scyld.com
Scyld Computing Corporation		http://www.scyld.com
914 Bay Ridge Road, Suite 220		Scyld Beowulf cluster system
Annapolis MD 21403			410-990-9993