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This document helps troubleshoot a system that does not respond. The document also discusses the cause, and how you can eliminate the problem.

A router appears to stop working when the edfing is not responsive to the console or to queries sent from the network for example, Telnet, Simple Network Management Protocol SNMPand so on. These problems can be classified into two broad categories:.

The information in this document was created from the devices in a specific lab environment. All of the devices used in this rouger started with a cleared default configuration. If your network is live, make sure that you understand the potential impact of any command. For more information on document conventions, refer to the Cisco Technical Tips Conventions.

Console problems occur when the router becomes unresponsive to input at the console port. If the console is not responsive, it means that a high priority process prevents the console driver from responding to input. Verify the router Router edging bits not working status. If all LEDs are down, it is most likely an issue with the power supply of the router. Disconnect network interfaces and see if the router responds.

Many times the router assumes it is doing something too important to service exec sessions. The scheduler allocate command hits CPU time for low priority processes. It puts a maximum time allocated to fast-switching microseconds - usec and process-switching usec routeg network interrupt context.

If the console does not respond because the router CPU utilization is high, it is important to find and correct the cause router edging bits not working the high CPU utilization. For example, if process-switched IP traffic causes problems, then this is reflected in the "IP Input" process in the output from the show processes cpu command.

In this situation, it is important to collect the output from show interfacesshow interfaces statand possibly show processes to further diagnose the problem. To fix the problem, you would need to reduce the amount of IP traffic that is process switched. Another possible cause of an apparent hang is memory allocation failure; that is, either the router edging bits not working has used all available memory, or the memory has been fragmented into such small pieces that the router cannot find a usable available block.

For more information, see Troubleshooting Memory Problems. The router can stop responding due to a security-related problem, such as a worm or virus. This is especially likely to be the cause if there have not been recent changes to the network, such as a router IOS upgrade.

Usually, a configuration change, such as adding additional lines to your access lists can mitigate the effects of this problem. The Cisco Security Advisories and Notices page contains information on detection of the most likely causes and specific workarounds.

Cisco Threat Control. If the router appears to freeze during the bootup process, it can be the result of an improperly configured feature or of a software defect in a configured feature.

This is often evident from the appearance of a warning or error message on the console immediately before the router freezes. As a workaround to this problem, boot router edging bits not working router into ROMMON, and bypass the workinv configuration, and then configure it again.

Edgng these steps:. Change the configuration register to 0x and then reset the router. This causes the router to boot from Flash without loading the configuration. Now, you can save an empty configuration all commands removed. Issue the router edging bits not working running-config startup-config command. Alternatively, if you suspect that a certain command causes the problem, you can edit the configuration. To do so, issue the copy startup-config running-config command.

Then type configure terminaland make the changes. When finished, change the configuration-register back to 0x For this, type config-register 0x Issue the copy running-config startup-config command to commit the changes. If worikng no longer passes through the router and the console is unresponsive, there is routter a problem with the system.

Generally this means that the router is caught in a continuous loop or stuck at a function. This is almost always egding by a bug in the software. Install the most recent maintenance release of the Cisco IOS software train you currently run.

Obtaining stack traces during a problem makes it possible to determine where in the code the router is looping or stuck. Traffic problems occur when the console remains responsive but traffic does not pass through the router.

Router edging bits not working this case, part of the traffic or part of the interfaces are not responsive. This behavior can be caused by a variety of different causes. When this problem occurs, information can be collected from the router through the console port. The causes for these traffic problems can workinv from errors on the interfaces to software and hardware problems.

Routing issue — Changes in the network topology or in the configuration of some routers could have affected the routing tables. Interface down — One of the router interfaces can be down. There are multiple events that could cause this, which can range from a wrong configuration command to a hardware failure of the interface or the cable. If some interfaces appear down when you issue a show interfaces command, try to find out what caused it.

Wedged interfaces — This is a particular case of buffer leaks that causes the input router edging bits not working of an interface to fill up to the point where it can no longer accept packets.

Reload the router. This frees that input queue, and restores traffic until the queue is full again. This can take anywhere from a few seconds to a few weeks, based on the severity of router edging bits not working leak. The easiest way to identify a wedged interface is router edging bits not working issue a show interfaces command, and to look for something similar to this:.

See Troubleshooting Buffer Leaks for detailed guidelines and examples. K-trace refers to the procedure used to obtain a stack trace from the router from ROM Monitor. On routers with older ROM Monitor code, a stack trace is obtained with the k command. On routers that run more recent ROM Monitor wdging, the stack command can also be used.

Enable the break sequence. For this, change the configuration register value. The eighth bit value must be set to zero so that break is not ignored. A value of 0x works.

Send the break douter when the problem occurs. Capture a stack trace. For this, collect the output from worknig the k 50 or stack 50 commands. Add 50 to the command to print a longer stack trace.

Repeat the three last steps several times to ensure that multiple points in a continuous loop have been captured. Repeat this procedure several times in the event of a system problem to collect multiple instances of the stack trace. When a router does not respond, router edging bits not working is almost always a software router edging bits not working. In this case, collect as much information as possible, including the stack trace, before you open a TAC service request.

It is also important to include output from the show versionshow runand show interfaces commands. Note: If the console is responsive, please do not manually router edging bits not working or power-cycle the router before collecting the above information, unless required to troubleshoot router hangs, as this can cause important information to be lost that is needed for determining the root cause of the problem.

Contents Introduction. Troubleshooting performed before opening the case show technical-support output in enable mode if possible show log output or console captures if available stack trace from ROM Monitor Please attach the collected data to your case in non-zipped, plain text format. If you cannot access the TAC Service Request Tool, you can attach router edging bits not working relevant information to your case by sending it to attach cisco.