Re: load balanced nic
On Sep 28, 2008, at 4:20 AM, Shane Chrisp wrote:
It is quite common practise to set the ports to what you need so that
the auto-negotiation does not get it wrong, in particular setting half
duplex instead of full duplex. This is not so common when its
"cisco connected to cisco", but very common when its "cisco
connected to
some other brand".
Cisco / Sun combinations are PARTICULARLY notorious for this
problem. They have never played nicely between their different forms
of auto-negotiation.
Hard-coding in the server room/closet, auto-negotiation for the PC's
on the general population network is VERY common. Hard-coding in a
data-center environment is also quite common.
One place where this falls down are fiber interfaces. The fiber specs
typically do things "right" without messing with them, and messing
with hard-setting fiber interfaces often leads to other trouble (human
error).
Hard-setting in cases where Ethernet distance lengths for higher
speeds have been exceeded can also be useful. The cable in use may
not consistently work well at a higher speed over long distances, but
will handle lower speed Ethernet just fine.
(Example: Very old buildings with Cat 3 type cabling in risers often
exhibits bad CRC error rates at 100 full. 100 half, or even 10 full/
half hard-set in the switch closet may save a small company struggling
for cash enough money and time to "get by" until the building's
distribution frame cabling can be upgraded. It's a stupid thing to
have to do, but it's better than thousands upon thousands of CRC
errors from old wiring counting up in all the switches.)
In short -- if anyone hasn't been around Ethernet long enough to have
seen times when hard-set settings and auto-negotiation can BOTH cause
trouble, they haven't seen it all yet. I have.
Try a call-center wired with Cat 3 25-pair in riser bundles to 110
punch blocks (old AT&T building) to Cat 5 STP (shielded, not
unshielded twisted pair) installed incorrectly with drain wires at
both ends tied to ground and at 3m punch blocks cross-connected to the
110's (remember those, anyone?) within a 1/8 mile of a high-powered AM
broadcast facility. (Yeah, that was fun.)
--
Nate Duehr
nate@natetech.com
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