Cisco Catalyst 2960 Series, Configuration Manual

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Speed and Duplex Configuration Guidelines
When configuring an interface speed and duplex mode, note these guidelines:
• Do not disable Auto-Negotiation on PoE switches.
• Gigabit Ethernet (10/100/1000-Mb/s) ports support all speed options and all duplex options (auto, half,
and full). However, Gigabit Ethernet ports operating at 1000 Mb/s do not support half-duplex mode.
• For SFP module ports, the speed and duplex CLI options change depending on the SFP module type:
◦ The 1000BASE- x (where - x is -BX, -CWDM, -LX, -SX, and -ZX) SFP module ports support the
nonegotiate keyword in the speed interface configuration command. Duplex options are not
supported.
◦ The 1000BASE-T SFP module ports support the same speed and duplex options as the
10/100/1000-Mb/s ports.
• If both ends of the line support autonegotiation, we highly recommend the default setting of auto
negotiation.
• If one interface supports autonegotiation and the other end does not, configure duplex and speed on both
interfaces; do not use the
auto setting on the supported side.
• When STP is enabled and a port is reconfigured, the switch can take up to 30 seconds to check for loops.
The port LED is amber while STP reconfigureAs best practice, we suggest configuring the speed and
duplex options on a link to auto or to fixed on both the ends. If one side of the link is configured to auto
and the other side is configured to fixed, the link will not be up and this is expected.s.
• As best practice, we suggest configuring the speed and duplex options on a link to auto or to fixed on
both the ends. If one side of the link is configured to auto and the other side is configured to fixed, the
link will not be up and this is expected.
Changing the interface speed and duplex mode configuration might shut down and re-enable the interface
during the reconfiguration.
Caution
IEEE 802.3x Flow Control
Flow control enables connected Ethernet ports to control traffic rates during congestion by allowing congested
nodes to pause link operation at the other end. If one port experiences congestion and cannot receive any more
traffic, it notifies the other port by sending a pause frame to stop sending until the condition clears. Upon
receipt of a pause frame, the sending device stops sending any data packets, which prevents any loss of data
packets during the congestion period.
The switch ports can receive, but not send, pause frames.
Note
You use the flowcontrol interface configuration command to set the interface
’
s ability to receive pause frames
to on , off , or desired . The default state is off .
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
23
Information About Configuring Interface Characteristics