Allied Telesis 2.6.1 manual Autonegotiation of Port Speed and Duplex Mode

66 AT-8800 Series Switch User Guide

Autonegotiation of Port Speed and Duplex Mode

Each of the switch ports can operate at either 10 Mbps or 100 Mbps, in either full duplex or half duplex mode. In full duplex mode a port can transmit and receive data simultaneously, while in half duplex mode the port can either transmit or receive, but not at the same time. This versatility makes it possible to connect devices with different speeds and duplex modes to different ports on the switch. Such versatility also requires that each port on the switch know which speed and mode to use.

Autonegotiation allows the ports to adjust their speed and duplex mode to accommodate the devices connected to them. Each switch port can be either configured with a fixed speed and duplex mode, or configured to autonegotiate speed and duplex mode with a device connected to it to determine a speed and mode that will allow successful transmission. An autonegotiating port will adopt the speed and duplex mode required by devices connected to it. If another autonegotiating device is connected to the switch, they will negotiate the highest possible common speed and duplex mode (Table 8 on page 67). Setting the port to a fixed speed and duplex mode allows it to support equipment that cannot autonegotiate.

It is also possible to require a port to operate at a single speed without disabling autonegotiation by allowing the port to autonegotiate but constrain the speed/duplex options to the desired combination. For example, if one end of a link is set to AUTO and other to 100MFULL then the AUTO end will select 100MHALF operation because without the other end autonegotiating the AUTO end has no way of knowing that the fixed end is full duplex capable. If a particular speed is required it is usually preferable to fix the speed/duplex combination using one of the autonegotiating speed values. Therefore, using 100MFAUTO at one end of a link and will allow the AUTO end to autonegotiate 100MFULL.

Switch ports will autonegotiate by default when they are connected to a new device. To change this setting, use the command:

SET SWITCH PORT={port-listALL} SPEED={AUTONEGOTIATE10MHALF10MFULL10MHAUTO10MFAUTO10 0MHALF100MFULL100MHAUTO100MFAUTO1000MHALF1000MFULL1 000MHAUTO1000MFAUTO}

Autonegotiation can also be activated at any time after this, on any port that is set to autonegotiate, by using the command:

ACTIVATE SWITCH PORT={port-listALL} AUTONEGOTIATE

On the first switch, the gigabit uplink ports always use 1000 Mbps speed and operate in full duplex mode, but these ports can also autonegotiate with peers in order to successfully pass the negotiation phase to get to successful operation.

Software Release 2.6.1 C613-02039-00 REV A