Cisco 2975 - Manual (Page 41)

3-3
Catalyst 2975 Switch Hardware Installation Guide
OL-17784-01
Chapter 3 Troubleshooting
Diagnosing Problems
10/100/1000 PoE Port Connections
When a powered device connected to PoE port does not receive power, you should:
• Use the Mode button to show the PoE status for all ports. See Table 1-6 and Table 1-7 for
descriptions of the LEDs and their meanings.
• Verify the port status by using the show interfaces privileged EXEC command to see if the port is
in error-disabled, disabled, or shutdown. Re-enable the port if necessary.
• Verify that the power supply installed in the switch meets the power requirements of your connected
devices. See the
“RPS Connector” section on page 1-9 for more information.
• Verify the cable type. Many legacy powered devices, including older Cisco IP phones and access
points that do not fully support IEEE 802.3af, might not support PoE when connected to the switch
by a crossover cable. Replace the crossover cable with a straight-through cable.
Caution PoE faults are caused when noncompliant cabling or powered devices are connected to a PoE
port. Only standard-compliant cabling can be used to connect Cisco prestandard IP phones
and wireless access points or IEEE 802.3af-compliant devices to PoE ports. (You must
remove a cable or device that causes a PoE fault from the network.)
SFP Module Issues
Use only Cisco SFP modules on the switch. Each Cisco module has an internal serial EEPROM that is
encoded with security information. This encoding provides a way for Cisco to identify and validate that
the module meets the requirements for the switch. Check these items:
• Bad or wrong SFP module. Exchange the suspect module with known good module. Verify that the
module is supported on this platform. (The switch release notes on Cisco.com list the SFP modules
that the switch supports.)
• Use the show interfaces privileged EXEC command to see if the port or module is error-disabled,
disabled, or shutdown. Re-enable the port if needed.
• Make sure that all fiber connections are properly cleaned and securely connected.
Interface Settings
An obvious but sometimes overlooked cause of port connectivity failure is a disabled interface. Verify
that the interface is not disabled or powered off for some reason. If an interface is manually shut down
on one side of the link or the other side, the link does not come up until you re-enable the interface. Use
the show interfaces privileged EXEC command to see if the interface is error-disabled, disabled, or
shutdown on either side of the connection. If needed, re-enable the interface.
Ping End Device
Ping from the directly connected switch first, and then work your way back port by port, interface by
interface, trunk by trunk, until you find the source of the connectivity issue. Make sure that each switch
can identify the end device MAC address in its Content-Addressable Memory (CAM) table.
Spanning Tree Loops
STP loops can cause serious performance issues that look like port or interface problems.