From: jbarratt (jbarratt@COMPSAT.COM)
Date: Fri Jan 16 2004 - 12:40:05 EST
I have no doubt your network staff is top notch, nor do I have any doubt
that autonegotiate fits your needs. However, I believe that attempting
to preach the benefits of autonegotiate in your environment does a
disservice to those in other environments who may be unaware of the
possible issues that autonegotiate can create.
Yes autonegotiate works. However, you may negotiate at a rate that is
not optimal in a switched environment. if you are in an environment that
is loaded with hubs, you will not want to force adapters to Full Duplex,
as you will get a lot of CRC errors and collisions, and performance will
suffer. MOST modern shops today do not have a ton of hubs in the network
closets.
Assuming you are using 100Mb ethernet adapters; if you are are not
forcing either the ports on the switches at 100/FULL and/or the adapter
at 100/FULL, you MAY be negotiating at 100/HALF. For many reasons
100/HALF may not be the rate/duplex you want to be negotiating at, and
performance may suffer. For those who contend that there is no/minimal
performance difference between full and half duplex, or have the bizarre
belief that 'most of our network traffic is uni-directional' a simple
timed ftp will quash that argument.
Attached is from the usenix library regarding half duplex:
In full-duplex mode, frames travel in both directions simultaneously
over two channels on the same connection for an aggregate bandwidth of
twice that of half-duplex mode
If you do not control the speed of the adapters/ports, you are at the
mercy of the autonegotiate methods. And performance may suffer. This is
is the true problem with autonegotiate.
I don't know about the shop you work in, but the shops I work in would
be very upset if I built a non-optimal solution without discussing the
reason I was using the non-optimal solution.
You can identify the speed adapters are running at by using:
netstat -v |grep Speed
Will both report the speed setting and the speed that is being
negotiated (on newer adapters).
btw. I never autonegotiate. That is the equivalent of leaving the link
speed up to chance.
Jeff Barratt-McCartney
Compsat Technology
248-223-1020 x337
248-320-3927 cell
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