Full or half duplex

[h.wall]

I am in a never ending argument with my server group about nic settings. Microsoft is misloading them by saying the servr should be auto and the switch shpould determine the speed. I explained that this would cause may errors. My question is what is better reliability wise, half duplex or full. Does anyone half a good url to describe the differnces in detail. I would like them to read it. Thanks.

[glen.grant]

Unless you are having a problem with errors on a port auto should work fine most of the time . If you hardcode the speed/duplex then both ends must be hardcoded . Always use full duplex if possible , this eliminates the collision domain for the link .

[allan.thomas]

Have look at the following URL:

http://www.cisco.com/en/US/tech/tk389/tk214/technologies_tech_note09186a0080094781.shtml

The main problem is that if the switch is unable to determine the duplex setting, the switch will operate at 100FD per if configured at 100FD. However the server nic will default to half-duplex when set to auto and will result in a duplex mismatch.

Hope this helps

Allan.

[Kevin Dorrell]

I think the Microsoft technician is misleading you here. He seems to be recommending auto on the NIC and fixed on the switch, BUT, that is precisely the combination that does not work correctly. The reason is that if you fix the speed and duplex on the switch, it disables the negotiation, so the NIC falls back to the default: half-duplex.

Why Cisco chose to do this, I have no idea. It would quite feasible under the protocol for the switch to negotiate "I want 100-full only". But Cisco, for reasons best known to them, chose not to implement it like that. The result is that "auto vs. fixed" makes a duplex mismatch.

You should have auto on both NIC and switch, or fixed on both NIC and switch. I would recommend auto at both ends.

Here is the document you are looking for:

http://www.cisco.com/en/US/tech/tk389/tk214/technologies_tech_note09186a0080094781.shtml

P.S. Sorry, I just saw that Allan Thomas got there first!

Hope this helps.

Kevin Dorrell

Luxembourg