Sunday, October 24, 2010

Cisco: The Top 7 Problems that People Think Are Hardware, But Are Not

Cisco: The Top 7 Problems that People Think Are Hardware, But Are Not

Cisco TAC has put together a list of router issues that are commonly perceived to be due to a hardware failure, but can normally be fixed more quickly without replacing anything. While some of these may in fact be due to hardware failures, it doesn't usually make sense to start with that assumption. Save yourself some time by checking more common causes first.

#1 The system reports error messages mentioning memory, or an interface chipset. Most of these issues are due to software, or are merely informational. Use the system error message decoder with your output.

#2 No response on the console, but the device appears to be working otherwise. Most of these problems are due to an incorrect cable, or incompatible terminal settings - especially flow control.

#3 The system restarts by itself (crashes). Some crashes are due to hardware, but the majority are software issues. Use the Output Interpreter with the output of "show tech" as a first pass, or open a service request with TAC.

#4 A module or interface card is unrecognized. If the IOS version is too new, or the hardware is otherwise unsupported by the software, modules may not be seen. This is almost always a mismatch between the software required and the hardware installed.

#5 The configuration is lost upon a power cycle. This can happen if the config-register is not reset after doing a password recovery, as explained in this tech tip:

In additional, failure to save the configuration after a change is also fairly common.

#6 Errors reported in show interface output. Most errors are either normal, but unusual conditions (drops, e.g.) or due to an external cause like incorrect clocking, noise, or even a marginal cable. Rule those out first.

#7 Wrong version loaded, or failure to completely boot. Again, the config-register can easily cause unexpected behavior. Check the config-register and boot system commands, and beware of relying on the system to boot the first image in flash.

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