Recommended Port Configuration (Autonegotiation or Manual Configuration)
There are many opinions on the subject of autonegotiation. Previously, many engineers advised customers not to use autonegotiation with any switch-connected device. However, improvements in the interoperation of autonegotiation and the maturity of the technology has recently changed the view of autonegotiation and its use. In addition, performance issues due to duplex mismatches, caused by the manual setting of speed and duplex on only one link partner, are more common. Because of these recent issues, the use of autonegotiation is regarded as a valid practice.
Maintaining Link (Link Up/Down Situations)
Under certain circumstances, interoperability issues between Cisco switches and various NICs can result in continuous or intermittent link up/down situations. These link up/down situations are usually a result of power management features or jitter tolerance issues associated with the NIC.