NetworkAutonegtiate
Auto-negotiation is not 100% reliable, but it does generally work.
Links with a duplex mismatch will operate, but will generate large numbers of errors, and can slow down busy networks.
For most interfaces, both speed and duplex need to be set to auto for full auto-negotiation to work.
Forcing a Catalyst switch port to a specific speed disables auto-negotiation for the duplex setting.
Full-duplex mode can be achieved only if both sides of the link are either set to auto-negotiate or manually configured to use full-duplex.
Full-duplex will work only if a host is connected directly to a switch or other device, with no repeaters or hubs in-between.
If auto-negotiation is enabled on only one side of the link, it will always default to half-duplex, regardless of what the other side of the link is forced to.
If one side of a link is forced to full duplex and the other is set to auto-negotiation, a duplex mismatch will occur.
You can force a new auto-negotiation by simply unplugging a host cable for 10 seconds.
Most 10 Mb interfaces can run only in 10Mb half-duplex mode.
Most 10/100 Mb interfaces can do auto-negotiation. Most 10/100 Mb interfaces with RJ-45 twisted pair jacks can run in full-duplex mode.
Any network connected via an AUI port (with an external transceiver, for example) can run only in 10Mb half-duplex mode.
==> What works:
AUTO <> AUTO
FULL <> FULL
AUTO <> HALF
HALF <> HALF
==> What doesn't Work:
AUTO <> FULL
HALF <> FULL