Preventing Autonegotiation Mismatches; Troubleshooting Power Over Ethernet Switch Ports; Sfp Module Security And Identification - Cisco WS-C3750-48PS-S Software Configuration Manual

Chapter 39 Troubleshooting

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) and duplex (half or full). There are situations when this
protocol can incorrectly align these settings, reducing performance. A mismatch occurs under these
circumstances:
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•
To maximize switch performance and ensure a link, follow one of these guidelines when changing the
settings for duplex and speed:
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•
If a remote device does not autonegotiate, configure the duplex settings on the two ports to match. The
Note
speed parameter can adjust itself even if the connected port does not autonegotiate.

Troubleshooting Power over Ethernet Switch Ports

If a powered device (such as a Cisco IP Phone 7910) that is connected to a Power over Ethernet (PoE)
switch port and is being powered by an AC power source loses power from the AC power source, the
device might enter an error-disabled state. To recover from an error-disabled state, enter the shutdown
interface configuration command, and then enter the no shutdown interface command. Another method
to recover the interface from the error-disabled state is to have automatic recovery configured on the
switch. The errdisable recovery cause loopback and the errdisable recovery interval seconds global
configuration commands automatically take the interface out of error-disabled state after the specified
period of time.
Use these commands, described in the command reference for this release, to monitor PoE port status:
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SFP Module Security and Identification

Cisco-approved small form-factor pluggable (SFP) modules have a serial EEPROM that contains the
module serial number, the vendor name and ID, a unique security code, and cyclic redundancy check
(CRC). When an SFP module is inserted in the switch, the switch software reads the EEPROM to verify
the serial number, vendor name and vendor ID, and recompute the security code and CRC. If the serial
number, the vendor name or vendor ID, the security code, or CRC is invalid, the software generates a
security error message and places the interface in an error-disabled state.
78-16180-02
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.
show controllers power inline privileged EXEC command
show power inline privileged EXEC command
debug ilpower privileged EXEC command
Preventing Autonegotiation Mismatches
Catalyst 3750 Switch Software Configuration Guide
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