A P P E N D I X

A P P E N D I X A

Auto-Negotiation

An understanding of auto-negotiation will help you manage your Sun eri FastEthernet interface. Auto-negotiation automates the speed and mode of the interface. Auto-negotiation detects the link partner capabilities and accommodates to them.

The Auto-Negotiation Protocol

Autonegotiation is a key feature of the Sun eri FastEthernet driver. The auto-negotiation protocol, as specified by the 100BASE-T IEEE 802.3u Ethernet Standard , selects the operation mode (half-duplex or full-duplex), and the auto-sensing protocol selects the speed (10 Mbps or 100 Mbps) for the adapter.

Boot Process on the Network

The auto-negotiation protocol does the following when the system is booted:

Identifies all link partner-supported modes of operation
Advertises its capabilities to the link partner

Selects the highest common denominator mode of operation based on the following priorities (in decreasing order):

Priority	Line Speed and Mode
First	100 Mbps, full-duplex
Second	100 Mbps, half-duplex
Third	10 Mbps, full-duplex
Fourth	10 Mbps, half-duplex

The link partner is the networking device (system, Ethernet hub, or Ethernet switch) at the other end of the link or cable.

Correcting Errors in Negotiating

If the SUNW,eri device is connected to a remote system or interface that is not capable of auto-negotiation, your system automatically selects the correct speed and half-duplex mode.

If the Sun eri FastEthernet is connected to a link partner with which the auto-negotiation protocol fails to operate successfully, you can configure the device so it does not use this protocol. This forces the driver to set up the link in the mode and speed of your choice.

Internal (Local) Transceiver

The internal transceiver also supports a forced mode of operation. This is where the user selects the speed and mode using the ndd utility, by editing the /etc/system file, or by creating an eri.conf file in the kernal/drv/ directory. The ndd utility makes calls to the eri driver to choose the speed and mode.