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Internetworks come in a variety of topologies and levels of complexity---from single-protocol, point-to-point links connecting cross-town campuses, to highly meshed, large-scale wide-area networks (WANs) traversing multiple time zones and international boundaries. The industry trend is toward increasingly complex environments, involving multiple media, multiple protocols, and often interconnection to unknown networks.
As a result, the potential for connectivity and performance problems in internetworks is high, and the source of such problems is often elusive. The goal of this publication is to help you isolate and resolve the most common connectivity and performance problems for your ATM switch as it fits into your network environment.
This chapter is separated into the following sections:
Failures in internetworks are characterized by certain symptoms. These symptoms might be general (such as clients that are unable to access specific servers) or more specific (routes that are not in the routing table). Each symptom can be traced to one or more problems or causes by using specific troubleshooting tools and techniques. Once identified, each problem can be remedied by implementing a solution that consists of a series of actions.
This publication describes how to define symptoms, identify problems, and implement solutions in the ATM switch environments. Always apply the specific context in which you are troubleshooting to determine how to detect symptoms and diagnose problems for your specific environment.
Figure 1-1 illustrates the process flow for the general model of problem-solving. This process is not a rigid outline for troubleshooting an internetwork. It is a foundation from which you can build a problem-solving process to suit your particular environment.
The following steps detail the problem-solving process outlined in Figure 1-1:
Step 1 When analyzing a network problem, make a clear problem statement. You should define the problem in terms of a set of symptoms and potential causes.
To do this, identify the general symptoms and then ascertain what kinds of problems (causes) could result in these symptoms. For example, hosts might not be responding to service requests from clients (a symptom). Possible causes might be a misconfigured host, bad interface port adapters, or missing configuration commands.
Step 2 Gather the facts you need to help isolate possible causes.
Ask questions of affected users, network administrators, managers, and other key people. Collect information from sources such as network management systems, protocol analyzer traces, output from switch diagnostic commands, or software release notes.
Step 3 Consider possible problems based on the facts you gathered. Using the facts you gathered, you can eliminate potential problems from your list.
For example, depending on the data, you might be able to eliminate hardware as a problem, and you can focus on software problems. At every opportunity, try to narrow the number of potential problems so that you can create an efficient plan of action.
Step 4 Create an action plan based on the remaining potential problems. Begin with the most likely problem and devise a plan in which only one variable is manipulated.
With this approach, you can reproduce a given solution to a specific problem. If you alter more than one variable simultaneously, you might solve the problem, but identifying the specific change that eliminated the symptom becomes more difficult.
Step 5 Implement the action plan, performing each step carefully while testing to see if the symptom disappears.
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.
Analyze the results to determine whether the problem has been resolved. If it has, then the process is complete.
Step 7 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 and reiterate the process until the problem is solved.
Make sure to undo any "fixes" that you made while implementing your action plan. Remember that you want to change only one variable at a time.
1. Do you have an accurate physical and logical map of your internetwork?
2. Do you have a list of all network protocols implemented in your network?
3. Do you know which protocols are being routed?
4. Do you know which protocols are being bridged?
5. Do you know all the points of contact to external networks, including any connections to the Internet?
If you can answer yes to these questions, you will be able to recover from a failure more quickly and more easily than if you are not prepared.
This section describes where to find general procedures for troubleshooting ATM switch hardware and booting problems. Always refer to the following hardware installation and maintenance publications for more detailed information about specific hardware, including descriptions of specific LEDs, configuration information, and additional troubleshooting information:
Refer to the following publications for specific software configuration and command reference information:
Refer to the chapter "Troubleshooting Hardware and Booting Problems" of the Internetwork Troubleshooting Guide for general information describing booting problems.
This section describes where to find general procedures for troubleshooting ATM switch Ethernet LAN media-related problems. The information referred her to is by no means comprehensive. Instead, it offers solutions to the problems most commonly encountered when using the particular media.
Always refer to the LightStream 1010 ATM Switch ASP Configuration Guide hardware installation and maintenance publication for more detailed information about specific Ethernet LAN media problems, including descriptions of specific LEDs, configuration information, and additional troubleshooting information.
Refer to the following publications for specific software configuration and command reference information:
Refer to the chapter "Troubleshooting LAN Media Problems" of the Internetwork Troubleshooting Guide for general information describing Ethernet LAN media problems.
This sections describes where to find general troubleshooting information and a discussion of tools and techniques for troubleshooting console line, auxiliary line, and dialup modem connections.
Always refer to the LightStream 1010 ATM Switch ASP Configuration Guide hardware installation and maintenance publication for more detailed information about specific Ethernet, auxiliary and console port connection information, including descriptions of specific LEDs, configuration information, and additional troubleshooting information.
Refer to the following publications for specific software configuration and command reference information:
Refer to the chapter "Troubleshooting Dialin Connections" of the Internetwork Troubleshooting Guide for general information describing Ethernet, auxiliary, and console port connection problems.
Always refer to the LightStream 1010 ATM Switch ASP Configuration Guide hardware installation and maintenance publication for more detailed information about specific TCP/IP configuration, including configuration descriptions, and additional troubleshooting information."
Refer to the following publications for specific software configuration and command reference information:
Refer to the chapter "Troubleshooting TCP/IP" of the Internetwork Troubleshooting Guide for general information describing TCP/IP configuration problems.
Posted: Fri Apr 9 10:24:32 PDT 1999
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