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autonegotiation
Purpose
Use the autonegotiation command to configure the Ethernet interface for automatic speed and
duplex operation. Use the no version of this command to disable autonegotiation.
Using autonegotiation allows the Ethernet interface to automati-
cally configure the speed and duplex. If the speed is manually set
to 10 or 100, the duplex must be manually configured as duplex
full or duplex half.
Syntax Description
The autonegotiation command has no subcommands.
Default Values
By default, all Ethernet interfaces are configured for autonegotiation.
Command Modes
The Ethernet Interface Configuration Mode is required for this command.
Functional Notes
Full-duplex Ethernet is a variety of Ethernet technology currently being standardized by the
IEEE. Because there is no official standard, vendors are free to implement their independent
versions of full-duplex operation. Therefore, it is not safe to assume that one vendor's
equipment will work with another.
Devices at each end of a full-duplex link have the ability to send and receive data
simultaneously over the link. Theoretically, this simultaneous action can provide twice the
bandwidth of normal (half-duplex) Ethernet. To deploy full-duplex Ethernet, each end of the
link must only connect to a single device (a workstation or a switched hub port). With only two
devices on a full-duplex link, there is no need to use the medium access control mechanism
(to share the signal channel with multiple stations) and listen for other transmissions or
collisions before sending data.
Half-duplex Ethernet is the traditional form of Ethernet that employs the Carrier Sense
Multiple Access/Collision Detect (CSMA/CD) protocol to allow two or more hosts to share a
common transmission medium while providing mechanisms to avoid collisions. A host on a
half-duplex link must "listen" on the link and only transmit when there is an idle period.
Packets transmitted on the link are broadcast (so it will be "heard" by all hosts on the
network). In the event of a collision (two hosts transmitting at once), a message is sent to
inform all hosts of the collision and a backoff algorithm is implemented. The backoff algorithm
requires the station to remain silent for a random period of time before attempting another
transmission. This sequence is repeated until a successful data transmission occurs.
61200630L1-35C
Ethernet Interface Configuration Command Set
NOTE
41
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