Interface Settings; Ping End Device; Spanning Tree Protocol Loops - Cisco Catalyst 3650 Series Hardware Installation Manual

Diagnosing Problems
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Note
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Interface Settings

Verify that the port or interface is not disabled or powered off. If a port or interface is manually shut
down on either side of the link, it 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 shut down 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's MAC address in its content-addressable memory (CAM) table.

Spanning Tree Protocol Loops

Spanning Tree Protocol (STP) loops might cause serious performance issues that resemble port or
interface problems.
A unidirectional link might cause loops. A loop occurs when the traffic sent by a switch is received by
the neighbor, but the traffic from the neighbor is not received by the switch. A broken cable, other
cabling problems, or a port issue could cause this one-way communication.
You can enable UniDirectional Link Detection (UDLD) on the switch to help identify unidirectional link
problems. For information about enabling UDLD on the switch, see the "Understanding UDLD" section
in the Cisco Catalyst 3650 Series Switches Software Configuration Guides at
http://www.cisco.com/c/en/us/support/switches/catalyst-3650-series-switches/products-installation-an
d-configuration-guides-list.html.
Catalyst 3650 Switch Hardware Installation Guide
5-4
Verify that the module is supported on Cisco Catalyst 3650 switches. (The switch's release note on
Cisco.com lists the SFP and SFP+ modules that the switch supports.) See the Cisco Catalyst 3650
Series Switches Release Notes at
http://www.cisco.com/c/en/us/support/switches/catalyst-3650-series-switches/products-release-not
es-list.html.
Use the show interfaces privileged EXEC command to see if the port or module is error-disabled,
disabled, or shut down. Re-enable the port, if needed.
Make sure that all the fiber connections are clean and securely connected.
For CX1 module connections and fiber connections, make sure that cable routing does not violate
the minimum allowed cable bend radius. See the documentation pertaining to the corresponding
module for specific cabling requirements.
When ordering or using CX1 cables, ensure that the version identifier is 2 or higher.
For long-wave SFP+ modules, a mode conditioning patch might improve performance over
maximum link distances with MMF connections.
When you insert several SFPs in multiple switch ports, wait for 5 seconds between inserting each
SFP. This will prevent the ports from going into error disabled mode. Similarly, when you remove
an SFP from a port, wait for 5 seconds before reinserting it.
Chapter 5 Troubleshooting
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