Introducing Stack Decoder
Welcome to the Stack Decoder!
Stack Decoder will help in those rare circumstances when a Cisco
router encounters a set of conditions it has not been programmed to
handle (for example during a hardware failure) and the router
generates a stack trace.
Stack traces can be displayed by executing the privileged command show stack from the exec prompt of the router. The stack trace is an important
feature of the Cisco IOS(tm) that allows the subsequent diagnosis and
repair of the underlying cause. [Cisco considers any situation which
results in a stack trace and restart (often called a crash) that is not due to
a hardware failure to be a software defect (even if the root cause is in fact
another malfunctioning device on the net).
How it works
Stack Decoder decodes the stack trace that the device generates and
creates a "symbol file". The symbol file, plus the other information in
the trace usually provides enough information to isolate the cause.
Prior to Stack Decoder, you would send the trace to the TAC to
decode the trace, analyze the related data, and compare the results to
our bug tracking database, diagnostic rules, and hardware address
Thanks to CCO's Bug Toolkit, you can use the
same techniques that the TAC uses and automates the process.
Once the trace has been analyzed, Stack Decoder presents an ordered
list of candidate diagnoses in a results list. The results list will
usually include a list of Bug ID's and/or a hardware diagnostic.
The last step is the most crucial and requires your input. The
first few defects listed usually contain the root cause of the problem.
Occasionally however, the diagnostic shows no clear winners. At this
point, careful attention must be paid to the software release levels,
protocols and conditions described in the bug citation. After
comparing all of the data, it is usually easy to identify the root cause.
- If I can't figure out the cause of the stack trace, what should I do?
- Select Open a case from the results page and Stack Decoder and simply paste the stack trace and any other relevant info (changes at the time the crash occurred, etc) and your contact information and CCO will open a case directly with the TAC. Even though no cause was identified, time will be saved by knowing what it is not!
- If I identify a bug as the probable cause what should I do?
- The bug citation will usually show the lowest software release that
the bug has been fixed in. In general, upgrading to the highest
maintenance revision available for that software release is the
For example, suppose the citation shows 10.2(5) as being the release
a bug is fixed in. At the same time, 10.2(8) is the current
maintenance revision level for that release. In this case, you would
probably want to upgrade to 10.2(8). Use of the Bug Navigator and
careful consideration of the Release Notes can help in determining
your action plan.
As always when making changes to your network, be sure and follow
proper change control procedures for optimum success.
- What if it looks like a hardware failure?
- In this situation it's best to open a case with the TAC, since their
assistance is still needed to ship the parts. Later releases of the Stack
Decoder will help in identifying the specific hardware part that is at
fault for improved problem resolution.