Chapter 7 Configuring the Switch Ports
Changing the Port Speed and Duplex Mode
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Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide
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Changing the Port Speed and Duplex Mode
Caution If you reconfigure the port through which you are managing the switch, a
Spanning Tree Protocol (STP) reconfiguration could cause a temporary loss of
connectivity.
Note The Ethernet link settings on the Long-Reach Ethernet (LRE) ports have
special considerations and different default settings than from the 10/100
ports. For this information, see the “LRE Ethernet Links” section on
page 7-25.
Follow these guidelines when configuring the duplex and speed settings:
• Gigabit Ethernet ports are always set to 1000 Mbps but can negotiate full or
half duplex with the attached device.
• Gigabit Ethernet ports that do not match the settings of an attached device
lose connectivity and do not generate statistics.
• Asynchronous Transfer Mode (ATM) ports are always set to full duplex and
do not autonegotiate duplex or speed settings.
• GigaStack-to-GigaStack stack connections operate in half-duplex mode, and
GigaStack-to-GigaStack point-to-point connections operate in full-duplex
mode.
• If STP is enabled, the switch can take up to 30 seconds to check for loops
when a port is reconfigured. The port LED is amber while STP reconfigures.
Connecting to Devices That Do Not Autonegotiate
To connect to a remote 100BASE-T device that does not autonegotiate, set the
duplex setting to Full or Half, and set the speed setting to Auto. Autonegotiation
for the speed setting selects the correct speed even if the attached device does not
autonegotiate, but the duplex setting must be explicitly set.
To connect to a remote Gigabit Ethernet device that does not autonegotiate,
disable autonegotiation on the local device, and set the duplex and flow control
parameters to be compatible with the other device.
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