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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

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