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Troubleshooting TechNotes

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Basic Concepts and Maintenance

"%Error opening tftp://255.255.255.255/network config" Error Message Prevention 03/Aug/2006
Back up and Restore Configuration Files 03/Aug/2006
Buffer Tuning for all Cisco Routers 17/Jun/2016
Capturing Text Output from Hyperterminal 25/Jun/2008
How to Protect Your Network Against the Nimda Virus 06/Mar/2008
How to Upgrade from ROMmon Using the Boot Image 27/Jan/2006
IPsec Troubleshooting: Understanding and Using debug Commands 15/Jul/2009
Maximum Number of Interfaces and Subinterfaces for Cisco IOS Routers: IDB Limits 24/May/2012
Performance Tuning Basics 11/Jul/2007
Problems Caused by Simultaneous Access to Router NVRAM 03/Aug/2006
Understanding the Definition of bits per second (bits/sec) from the show interfaces Command Output 01/Aug/2006
Understanding the Ping and Traceroute Commands 29/Nov/2006
Using Network-Based Application Recognition and ACLs for Blocking the "Code Red" Worm 02/Aug/2006

Boot Failure Recovery and IOS Upgrade

How to Choose a Cisco IOS Software Release 27/May/2015
How To Copy a System Image from One Device to Another 22/Sep/2014
Standard Break Key Sequence Combinations During Password Recovery 22/Sep/2014
TFTP Server Selection and Use 02/Feb/2006
Why Does My Router Lose Its Configuration During Reboot? 25/Jun/2008
Xmodem Console Download Procedure Using ROMmon 01/Feb/2006

High CPU Utilization

Dealing with mallocfail and High CPU Utilization Resulting From the "Code Red" Worm 20/Jun/2008
High CPU Utilization in Exec and Virtual Exec Processes 12/Dec/2008
Troubleshooting High CPU Utilization Due to Interrupts 29/May/2008
Troubleshooting High CPU Utilization due to Processes 29/Sep/2008
Troubleshooting High CPU Utilization in IP Input Process 11/Feb/2019
Troubleshooting High CPU Utilization on Cisco Routers 27/Apr/2016
What Causes %SYS-3-CPUHOG Messages? 24/Jun/2008

Troubleshooting Hardware

Processor Memory Parity Errors (PMPEs) 25/May/2016
SegV Exceptions 31/May/2016
Troubleshooting Buffer Leaks 26/May/2016
Troubleshooting Input Queue Drops and Output Queue Drops 03/May/2016
Troubleshooting Spurious Accesses, Alignment Errors, and Spurious Interrupts 31/May/2016
Troubleshooting Watchdog Timeouts 21/Jun/2016

Troubleshooting Router Hang and Router Crash

Creating Core Dumps 24/Jun/2008
Less Common Types of System Crashes 12/May/2016
Retrieving Information from the Crashinfo File 01/Feb/2006
Troubleshooting Bus Error Crashes 16/Jun/2016
Troubleshoot Router Crashes 18/Nov/2019
Troubleshooting Router Hangs 02/Aug/2006
Understand Software-forced Crashes 16/Jun/2016
What Causes a Router To Be Restarted By the Abort or Trace Trap Commands 29/Nov/2006

Miscellaneous

Configuring ISL Trunks on Cisco Routers 30/Aug/2005
Most Common L2L and Remote Access IPsec VPN Troubleshooting Solutions 31/Mar/2014
Understand the NM-HDV2 IP Communications High-Density Digital Voice or Fax Network Module 10/Aug/2006
Understanding and Configuring VLAN Routing and Bridging on a Router Using the IRB Feature 31/Aug/2009
Wireless LAN Controller Module (WLCM) Configuration Examples 19/Feb/2007

Support Documentation

All Support Documentation for this Series

Troubleshoot and Alerts

Field Notices (5)

Password Recovery (1)

Security Advisories, Responses and Notices (3)