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Troueblshooting Switching TechnologiesLennin Pérez

High Touch Technical Support Engineer

[email protected]

T-shoot

Topics

PHY Local Ports

CPU

STP

Memory

Stacking

PHY Link Ports

Troubleshooting Link Issues

How to detect a link failure in most of the cases?• Connectivity issues• Traffic lost

Troubleshooting Link Issues

• Is the link up/up?• Are packets being sent and received?• Are there any errors?• Collecting data multiple times help to confirm issues

Troubleshooting Link Issues

How to check link failure?

• Clear counters and monitor the port• Migrate port configuration to another port – Exclude faulty hardware• Check configured duplex and speed on both ends• Review “show log” output – Tracebacks, Rx – Tx messages

%SFF8472-5-THRESHOLD_VIOLATION: Gi1/0/6: Rxpower low warning; Operating value: -21.9 dBm, Threshold value: -19.5 dBm

Troubleshooting Link IssuesPossible cause Corrective Action

Wrong port Make sure that both ends of the cable are plugged intothe correct ports.

Wrong cable type Verify the cable selection.

Bad cable Swap suspect cable with known good cable. Look forbroken or missing pins on connectors.

Loose connections Check for loose connections. Sometimes a cableappears to be seated in the jack, but is not. Reinsert it.

Patch panels, Media convertors Bypass the patch panel or the media convertor ifpossible to rule it out.

Bad or wrong gigabit Interface Convertor (GBIC) Swap suspect GBIC with known good GBIC. Verify theGBIC type and that both ends are compatible.

Bad Port or Module Port or Interface or Module notenabled.

Move the cable to a known good port to troubleshoota suspect port or module. Use the “showinterface” command for Cisco IOS to look forerrdisable, disable or shutdown status. The showmodule command can indicate faulty, which canindicate a hardware problem.

CPU issues

Troubleshooting CPU issues

CPU Functions:• Runs the IOS• Processes Control Plane traffic (LACP / STP / CDP / etc.)• Processes packets that are not switched in Hardware• Communicate with controllers(s)

Troubleshooting CPU issues

What could be the cause?

• Processes taking up resources• Forwarded Network traffic (Interruptions)

Normal CPU utilization varies by:

• Switch model• Number of connected ports, modules, switches in stack (i.e. HUL LED Process)• Features set (LANBASE, IP BASE, IP SERVICES)

Troubleshooting CPU issues

Is high CPU an issue?

• HW switched traffic not impacted by high CPU• It’s an issue when these issues occur because control packets are not sent or received

• Spanning Tree Protocol (STP) reconverges• Routing protocol flaps• CLI is slow or unresponsive -> Sometimes this can be a memory issue too

Troubleshooting CPU issues

• Use the “show process cpu history” to display the history of CPU utilization• Is CPU always high? (Constant or spikes)• Is high only during business hours?

Troubleshooting CPU issues

• Use the “show process cpu sorted” or “show process cpu sorted | ex 0.00” to displaycurrent CPU utilization

Troubleshooting CPU issues

• If the CPU is not constant, how to identify the problem?

• Configure a CPU threshold policy“process cpu threshold type {total | process | interrupt}rising {percentage} interval {seconds} falling {percentage} interval {seconds}”

Example:

“process cpu threshold type process rising 70 interval 5 falling 30 interval 5”

Troubleshooting CPU issues

• Configure EEM script for more details:

STP

Troubleshooting STP issues

• What is STP?• Block redundant ports based on an STP algorithm, to resolve redundant physical topology

into a tree-like topology.• Why STP fails?• STP makes certain assumptions about its operational environment.

• Each link between the two bridges is bidirectional. • Each bridge that is running STP is able to regularly receive, process, and transmit STP

Bridge Protocol Data Units (BPDUs), also known as STP packets.

Troubleshooting STP issues

• Loss of connectivity• High CPU utilization• High link utilization (often 100 percent)• High switch backplane utilization (compared to the baseline utilization)• Syslog messages that indicate packet looping in the network (for example

HSRP duplicate IP address messages)• Syslog messages that indicate constant address relearning or MAC address

flapping messages• An increasing number of output drops on many interfaces

Troubleshooting STP issues

• Most STP troubleshooting revolves around three issues:1. Forwarding loops2. Excessive flooding due to a high rate of STP Topology

Changes (TC)3. Issues related to convergence time

Troubleshooting STP issues

Troubleshooting STP issues

• Spanning tree state forwarding in software?

Troubleshooting STP issues

MAC MOVES

Troubleshooting STP issues

Sep 29 08:05:35.450: %C4K_EBM-4-HOSTFLAPPING: Host 00:xx:bb:XX:0E:3e in vlan 890 is moving from port Po55 to port Gi6/17

Troubleshooting STP issues

Troubleshooting STP issues

Memory

Troubleshooting Memory issues

• Two Types of Memory:

• Processor memory is used by IOS Processes• I/O memory is used for CPU traffic

Troubleshooting Memory issues

• Don’t reload the box until appropiate data has been gathered to determine the issue.

• A reload alleviate the problem, but we lostimportant info!!!!!

• The problem will occur over the time

Troubleshooting Memory issues

Troubleshooting Memory issues

Troubleshooting Memory issues

• Memory Fragmentation: Sometimes it is a consequence of memory leak!!

• Check for Bugs• Open a TAC

case for furthert-shoot

Troubleshooting Memory issues

Troubleshooting Memory issues

Stacking

Troubleshooting Stacking issues

Troubleshooting Stacking issues

Troubleshooting Stacking issues

Troubleshooting Stacking issues

• How to add stack members?

Manually set switch priority

Troubleshooting Stacking issues

Troubleshooting Stacking issues

Thank you!!

Q & A