System information

Troubleshooting Overview 1-5
Preparing for Network Failure
Step 6 Whenever you change a variable, be sure to gather results. Generally, you should use the
same method of gathering facts that you used in Step 2 (that is, working with the key
people affected in conjunction with utilizing your diagnostic tools).
Step 7 Analyze the results to determine whether the problem has been resolved. If it has, then
the process is complete.
Step 8 If the problem has not been resolved, you must create an action plan based on the next
most likely problem in your list. Return to Step 4, change one variable at a time, and
reiterate the process until the problem is solved.
Note If you exhaust all the common causes and actions (either those outlined in this book or ones
that you have identified for your environment), you should contact your Cisco technical support
representative.
Preparing for Network Failure
It is always easier to recover from a network failure if you are prepared ahead of time. Possibly the
most important requirement in any network environment is to have current and accurate information
about that network available to the network support personnel at all times. Only with complete
information can intelligent decisions be made about network change, and only with complete
information can troubleshooting be done as quickly and easily as possible. During the process of
troubleshooting the network that it is most critical to ensure that this documentation is kept
up-to-date.
To determine whether you are prepared for a network failure, answer the following questions:
• Do you have an accurate physical and logical map of your internetwork?
Does your organization or department have an up-to-date internetwork map that outlines the
physical location of all the devices on the network and how they are connected, as well as a
logical map of network addresses, network numbers, subnetworks, and so forth?
• Do you have a list of all network protocols implemented in your network?
For each of the protocols implemented, do you have a list of the network numbers, subnetworks,
zones, areas, and so on that are associated with them?
• Do you know which protocols are being routed?
For each routed protocol, do you have correct, up-to-date router configuration?
• Do you know which protocols are being bridged?
Are there any filters configured in any bridges, and do you have a copy of these configurations?
• Do you know all the points of contact to external networks, including any connections to the
Internet?
For each external network connection, do you know what routing protocol is being used?
• Do you have an established baseline for your network?
Has your organization documented normal network behavior and performance at different times
of the day so that you can compare the current problems with a baseline?
If you can answer yes to all questions, you will be able to recover from a failure more quickly and
more easily than if you are not prepared.