[olug] Full Duplex - NIC

[Brian Roberson]

This is pretty well documented, but just for reference, and to get this on
the mailing list, below is a table of outcomes dependent on setting one side
of the Ethernet connection and not the other. This is true regardless of the
devices in use is a server, a switch, router, etc...

Client             Partner               Outcome
Auto               Auto                   Highest speed / Full duplex
100/Full          Auto                   Partner goes into 100/half
(mismatch)
100/half          Auto                   Partner goes into 100/half (ok)
10/Full           Auto                   Partner goes into 10/half
(mismatch)
10/half           Auto                   Partner goes into 10/half (ok)

It should be said, that many of us (me included) have found interoperability
issues when leaving the links to auto negotiate, especially cross vendor.
Which is why many times we just set it on both sides to enforce what it is
we want it to do.







On Wed, Feb 3, 2010 at 3:20 PM, Obi-Wan <obiwan at jedi.com> wrote:

> > In order to properly force a particular speed and/or duplex (say,
> > 100-Full) on a particular link, you need to set it on both link partners
> > - in this case, the the server and the switch it's connected to. If you
> > set one side but not the other you will cause a duplex mismatch.
>
> That's correct.  If you force an interface to particular settings
> instead of setting it to autonegotiate, then it won't bother announcing
> or negotiating its settings at all, and will instead just blindly
> assume that the other end has also been set to those same settings.
> If the other end has not been forced to those same settings (as when
> you've left it autonegotiate), then you'll have all sorts of network
> problems.
>
> Always leave your NICs set to autonegotiate unless you really know
> what you're doing and have a compelling reason to do otherwise.
>
> BTDT.
>
> --
> Ben "Obi-Wan" Hollingsworth                             obiwan at jedi.com
>   The stuff of earth competes for the allegiance I owe only to the
>     Giver of all good things, so if I stand, let me stand on the
>       promise that You will pull me through.  -- Rich Mullins
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