Resetting Counters on Cisco Switches

Introduction

Interface counters on Cisco switches provide crucial insights into network performance, error conditions, and traffic patterns. However, there are times when these counters need to be reset to establish new baselines or troubleshoot issues. This guide provides a comprehensive overview of counter management on Cisco switches, from basic concepts to advanced troubleshooting.

Learning Objectives

By the end of this guide, you will be able to:

• Understand different types of interface counters and their significance
• Execute counter reset commands with confidence
• Verify counter status and interpret results
• Troubleshoot common counter-related issues
• Implement counter management best practices

Main Content Sections

Part 1: Understanding Interface Counters

Types of Counters

• Input Counters
• Packets received
• Bytes received
• Input errors
• CRC errors
• Frame errors
• Input queue drops
• Output Counters
• Packets sent
• Bytes sent
• Output errors
• Collisions
• Interface resets
• Output queue drops

Counter Persistence

• Counters persist through normal device reloads
• Only cleared manually or during specific events
• Important for long-term monitoring
• Key component in capacity planning

Part 2: Counter Reset Commands

Basic Counter Reset

Switch# clear counters
Clear "show interface" counters on all interfaces [confirm]

Interface-Specific Reset

Switch# clear counters gigabitethernet 1/0/1
Clear "show interface" counters on this interface [confirm]

Verification Commands

Switch# show interfaces gigabitethernet 1/0/1

Understanding the Output:

GigabitEthernet1/0/1 is up, line protocol is up
  Hardware is Gigabit Ethernet, address is 0000.0000.0000
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 1000Mb/s, media type is 10/100/1000BaseTX
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:07, output 00:00:01, output hang never
  Last clearing of "show interface" counters 00:00:16
  Input queue: 0/75/0/0 (size/max/drops/flushes)
  Output queue: 0/40 (size/max)

Part 3: Best Practices and Workflows

Pre-Reset Checklist

1. Document current counter values
2. Verify maintenance window (if required)
3. Notify monitoring systems
4. Create backup of current statistics
5. Verify access privileges

Post-Reset Verification

1. Check counter reset timestamp
2. Verify zero values
3. Monitor new counter increments
4. Document reset in change log
5. Update monitoring systems

Troubleshooting Guide

Common Issues and Solutions

Issue 1: Counters Not Clearing

Symptoms:

• Counters remain unchanged after clear command
• Error messages during clear attempt

Solutions:

1. Verify privilege level
2. Check interface status
3. Confirm IOS version compatibility
4. Try alternate syntax
5. Clear specific counter types

Issue 2: Unexpected Counter Behavior

Symptoms:

• Rapid counter increments
• Unusual error patterns
• Inconsistent statistics

Solutions:

1. Check physical connectivity
2. Verify interface configuration
3. Monitor error counters
4. Compare with peer devices
5. Review system logs

Practical Exercise

Exercise: Counter Reset and Analysis

Objective

Reset interface counters and analyze the results over a 5-minute period.

Steps

1. Document initial counter values:

Switch# show interfaces gi1/0/1 | include packets

2. Clear interface counters:

Switch# clear counters gi1/0/1

3. Wait 5 minutes
4. Compare new values:

Switch# show interfaces gi1/0/1 | include packets

5. Analyze the rate of increment

Quick Reference

Essential Commands

show interfaces                 # View all interface statistics
show interfaces status         # View interface status summary
clear counters                 # Clear all interface counters
clear counters interface       # Clear specific interface counters
show interfaces counters       # View packet and byte counters

For detailed insights into monitoring and managing system statistics on Cisco routers, refer to Cisco’s CommandReference for System Monitoring. This guide provides comprehensive commands and examples tailored for effective system management.

Summary/Key Takeaways

• Counter resets are essential for accurate monitoring
• Always document before clearing counters
• Use interface-specific resets when possible
• Verify results after clearing
• Maintain proper change control procedures