On certain types of Twisted Pair Ethernet equipment, the speed, duplex mode and Pause capability of the link can be automatically negotiated, so that the link comes up in the highest performance configuration supported by both ends. In some cases, MDI/MDIX pair correction can also be negotiated.
Autonegotiation is supported only on some twisted pair interfaces, and only a very few Fiber interfaces.
When a device has mixed interfaces, some of which support autonegotiation and some of which do not, every interface will have an autonegotiation MIB variable. When the interface does not support autonegotiation, the associated MIB variable has a value of
Every port that autonegotiates must advertise the modes in which it is able and willing to operate. On some products, such as the CBFTF100, these modes can be enabled and disabled individually in order to exert influence over the mode in which the link runs.
Please read this important note regarding certain differences between Media Converters and Switches.