PHWinfo - Afficher un message - X-over accidentally connected from server to switch. But it worked!

20/03/2006, 20h29

WeeJockMacFeegle <WeeJockMacFeegle@gmail.com> wrote:
> Switch was set to 100Mb/Full, NICs auto set themselves at
> 100Mb/Half.

Some old boilerplate I trot-out from time to time:

How 100Base-T Autoneg is supposed to work:

When both sides of the link are set to autoneg, they will "negotiate"
the duplex setting and select full duplex if both sides can do
full-duplex.

If one side is hardcoded and not using autoneg, the autoneg process
will "fail" and the side trying to autoneg is required by spec to use
half-duplex mode.

If one side is using half-duplex, and the other is using full-duplex,
sorrow and woe is the usual result.

So, the following table shows what will happen given various settings
on each side:

Auto Half Full

Auto Happiness Lucky Sorrow

Half Lucky Happiness Sorrow

Full Sorrow Sorrow Happiness

Happiness means that there is a good shot of everything going well.
Lucky means that things will likely go well, but not because you did
anything correctly

Sorrow means that there _will_ be a duplex
mis-match.

When there is a duplex mismatch, on the side running half-duplex you
will see various errors and probably a number of _LATE_ collisions
("normal collisions don't count here). On the side running full-duplex
you will see things like FCS errors. Note that those errors are not
necessarily conclusive, they are simply indicators.

Further, it is important to keep in mind that a "clean" ping (or the
like - eg "linkloop" or default netperf TCP_RR) test result is
inconclusive here - a duplex mismatch causes lost traffic _only_ when
both sides of the link try to speak at the same time. A typical ping
test, being synchronous, one at a time request/response, never tries
to have both sides talking at the same time.

Finally, when/if you migrate to 1000Base-T, everything has to be set
to auto-neg anyway.

rick jones
--
oxymoron n, commuter in a gas-guzzling luxury SUV with an American flag
these opinions are mine, all mine; HP might not want them anyway...

feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

20/03/2006, 20h29	#7
Rick Jones Messages: n/a Hébergeur:	Re: X-over accidentally connected from server to switch. But it worked! WeeJockMacFeegle <WeeJockMacFeegle@gmail.com> wrote: > Switch was set to 100Mb/Full, NICs auto set themselves at > 100Mb/Half. Some old boilerplate I trot-out from time to time: How 100Base-T Autoneg is supposed to work: When both sides of the link are set to autoneg, they will "negotiate" the duplex setting and select full duplex if both sides can do full-duplex. If one side is hardcoded and not using autoneg, the autoneg process will "fail" and the side trying to autoneg is required by spec to use half-duplex mode. If one side is using half-duplex, and the other is using full-duplex, sorrow and woe is the usual result. So, the following table shows what will happen given various settings on each side: Auto Half Full Auto Happiness Lucky Sorrow Half Lucky Happiness Sorrow Full Sorrow Sorrow Happiness Happiness means that there is a good shot of everything going well. Lucky means that things will likely go well, but not because you did anything correctly Sorrow means that there _will_ be a duplex mis-match. When there is a duplex mismatch, on the side running half-duplex you will see various errors and probably a number of _LATE_ collisions ("normal collisions don't count here). On the side running full-duplex you will see things like FCS errors. Note that those errors are not necessarily conclusive, they are simply indicators. Further, it is important to keep in mind that a "clean" ping (or the like - eg "linkloop" or default netperf TCP_RR) test result is inconclusive here - a duplex mismatch causes lost traffic _only_ when both sides of the link try to speak at the same time. A typical ping test, being synchronous, one at a time request/response, never tries to have both sides talking at the same time. Finally, when/if you migrate to 1000Base-T, everything has to be set to auto-neg anyway. rick jones -- oxymoron n, commuter in a gas-guzzling luxury SUV with an American flag these opinions are mine, all mine; HP might not want them anyway... feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...