em0 and tunnel performance problem

Sean Chittenden sean at gigave.com
Wed Dec 28 13:09:17 PST 2005

> after digging deeper it found out that the whole em0 driver worth
> nothing...  when i set the media to auto it's operating in half
> duplex (i found out after a couple of benchmarks with iperf), when i
> set it to 100basetx and full duplex manually the result is worse...
> any idea?

Explicitly set the port speed on both the switch and client side, then
report back to the list.  As it stands, your environment is not setup
correctly, but this kind of misconfiguration seems to be a common
source of performance problems for some admins.

You can *never* rely on, or use auto negotiation.  Its very common to
have the switch be set to auto, the PC to be set to 100 FDX, and have
the switch settle on 100 half-duplex (Cisco switches in particular).
netstat -i will probably show you that you have line errors on your
em0 interface.  If you're running on Cisco switches, see the


If you're using a different brand of switches, see their respective
documentation.  Point being, auto-negotiation should never be used in a
production environment (though GigE handles this better).  -sc

Sean Chittenden

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