Preventing Autonegotiation Mismatches - Cisco Catalyst 3750 Software Configuration Manual

Metro switch

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Troubleshooting

Return to privileged EXEC mode:

Switch (config)# exit

Write the running configuration to the startup configuration file:

Switch# copy running-config startup-config

The new password is now in the startup configuration.

You must now reconfigure the switch. If the system administrator has the backup switch and VLAN

configuration files available, you should use those.

Preventing Autonegotiation Mismatches

The IEEE 802.3ab autonegotiation protocol manages the switch settings for speed (10 Mbps, 100 Mbps,

and 1000 Mbps, excluding SFP module ports unless the 1000-BASE-T SFP is installed) and duplex (half

or full). There are situations when this protocol can incorrectly align these settings, reducing

performance. A mismatch occurs under these circumstances:

To maximize switch performance and ensure a link, follow one of these guidelines when changing the

settings for duplex and speed:

If a remote device does not autonegotiate, configure the duplex settings on the two ports to match. The

speed parameter can adjust itself even if the connected port does not autonegotiate.

This procedure is likely to leave your switch virtual interface in a shutdown state. You can see

which interface is in this state by entering the show running-config privileged EXEC command.

To re-enable the interface, enter the interface vlan vlan-id global configuration command, and

specify the VLAN ID of the shutdown interface. With the switch in interface configuration

mode, enter the no shutdown command.

A manually-set speed or duplex parameter is different from the manually set speed or duplex

parameter on the connected port.

A port is set to autonegotiate, and the connected port is set to full duplex with no autonegotiation.

Let both ports autonegotiate both speed and duplex.

Manually set the speed and duplex parameters for the ports on both ends of the connection.

Preventing Autonegotiation Mismatches

Catalyst 3750 Metro Switch Software Configuration Guide