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This chapter presents information about the wide variety of tools available to assist you in troubleshooting your ATM switch.
This chapter consists of the following sections:
Cisco ATM switches provide numerous integrated commands to assist you in monitoring and troubleshooting your internetwork. This section, which describes the basic use of these commands, consists of the following sections:
The show commands are powerful monitoring and troubleshooting tools. You can use the show commands to perform a variety of functions including:
Following are some of the most commonly used show commands:
There are hundreds of other show commands available. For details on using and interpreting the output of specific show commands, refer to the LightStream 1010 ATM Switch Command Reference publication for your specific software version.
The debug privileged EXEC commands can provide a wealth of information about the traffic being seen (or not seen) on an interface, error messages generated by nodes on the network, protocol-specific diagnostic packets and cells, and other useful troubleshooting data.
 | Caution Exercise care when using debug commands. Many of these commands are processor intensive and can cause serious network problems (such as degraded performance or loss of connectivity) if they are enabled on an already heavily loaded switch. When you finish using a debug command, remember to disable it with its specific no debug command (or use the undebug all command to turn off all debugging). |
The appendix "Debugging" provides an overview of debug commands and their use when troubleshooting the ATM switch.
In many situations, third-party diagnostic tools can be more useful and less intrusive than using debug commands. For more information, see the section, "Using Third-Party Troubleshooting Tools," later in this chapter.
To check host reachability and network connectivity, use the ping EXEC (user) or privileged EXEC command. This command can be used to confirm basic network connectivity on IP networks.
Using the extended command mode of the ping command, you can specify the supported IP header options. This allows the switch to perform a more extensive range of test options. To enter ping extended command mode, enter yes at the extended commands prompt of the ping command.
It is a good idea to try the ping command when the network is functioning properly to see how the command works under normal conditions. Then when you are troubleshooting you can see the difference between normal and abnormal operation.
For detailed information on using the ping and extended ping commands, refer to the LightStream 1010 ATM Switch Software Command Reference publication.
The traceroute user EXEC command discovers the routes followed by the packets of a switch when traveling to their destinations. With the traceroute privileged EXEC command, the supported IP header options are specified, and the switch can perform a more extensive range of test options.
The traceroute command works by using the error message generated by switches when a datagram exceeds its time-to-live (TTL) value. First, probe datagrams are sent with a TTL value of one. This causes the first switch to discard the probe datagrams and send back "time exceeded" error messages. The traceroute command then sends several probes, and displays the round-trip time for each. After every third probe, the TTL is increased by one.
Each outgoing packet can result in one of two error messages. A "time exceeded" error message indicates that an intermediate switch has seen and discarded the probe. A "port unreachable" error message indicates that the destination node has received the probe and discarded it because it could not deliver the packet to an application. If the timer goes off before a response comes in, traceroute displays an asterisk (*).
The traceroute command terminates when the destination responds, when the maximum TTL is exceeded, or when the user interrupts the traceroute with the escape sequence.
As with ping, it is a good idea to use the traceroute command when the network is functioning properly to see how the command works under normal conditions. Then when you are troubleshooting you can see the difference between normal and abnormal operation.
For detailed information on using the traceroute and extended traceroute commands, refer to the LightStream 1010 ATM Switch Software Command Reference publication.
Cisco offers several network management products that provide design, monitoring, and troubleshooting tools to help you manage your internetwork.
The following Cisco internetwork management tools are useful for troubleshooting internetwork problems:
CiscoWorks for Switched Internetworks (CWSI) is a series of Simple Network Management Protocol (SNMP) based software management tools for large campus installations. These tools can discover the network at both the physical and logical layers, understand the connectivity between devices, and make configuration changes centrally (with distributed Web access) to all devices across the campus. These applications use a topological navigation system with automated layout utilities including zoom and collapse functions.
The CWSI bundle offers the following services and functionality:
CWSI is available across multiple platforms, including support for Windows NT, Solaris, HP-UX, and the AIX operating systems. CWSI also integrates the most current versions of CiscoView and TrafficDirector software.
The CiscoView, included within the CiscoWorks application, is a graphical user interface (GUI)-based device management application that provides dynamic status, statistics, and configuration information for the ATM switch. It displays a physical view of any Cisco device and shows real-time LED and interface status. The CiscoView application provides monitoring functions and simplifies basic troubleshooting tasks.
In many situations, third-party diagnostic tools can be more useful than commands that are integrated into the switch. For example, enabling a processor-intensive debug command can be disastrous in an environment experiencing excessively high traffic levels. However, attaching a network analyzer to the suspect network is less intrusive and is more likely to yield useful information without interrupting the operation of the switch.
Some typical third-party troubleshooting tools used for troubleshooting internetworks are described in the following sections:
Volt-ohm meters and digital multimeters are at the lower end of the spectrum of cable testing tools. These devices measure parameters such as AC and DC voltage, current, resistance, capacitance, and cable continuity. They are used to check physical connectivity.
Similar testing equipment is available for fiber-optic cable. Due to the relatively high cost of fiber cable and its installation, fiber-optic cable should be tested both before installation (on-the-reel testing) and after installation. Continuity testing of the fiber requires either a visible light source or a reflectometer. Light sources capable of providing light at the three predominant wavelengths, 850 nanometers (nm), 1300 nm, and 1550 nm, are used with power meters that can measure the same wavelengths and test attenuation and return loss in the fiber.
At the top end of the cable testing spectrum are time domain reflectometers (TDRs). These devices can quickly locate open and short circuits, crimps, kinks, sharp bends, impedance mismatches, and other defects in metallic cables.
A TDR works by "bouncing" a signal off the end of the cable. Opens, shorts, and other problems reflect the signal back at different amplitudes, depending on the problem. A TDR measures how much time it takes for the signal to reflect and calculates the distance to a fault in the cable. TDRs can also be used to measure the length of a cable. Some TDRs can also calculate the propagation rate based on a configured cable length.
Network monitors continuously track packets crossing a network, providing an accurate picture of network activity at any moment, or a historical record of network activity over a period of time. They do not decode the contents of frames. Monitors are useful for creating baselines in which the activity on a network is sampled over a period of time to establish a normal performance profile.
Monitors collect information such as packet sizes, the number of packets, error packets, overall usage of a connection, the number of hosts and their MAC addresses, and details about communications between hosts and other devices. This data can be used to create profiles of LAN traffic as well as assist in locating traffic overloads, planning for network expansion, detecting intruders, establishing baseline performance, and distributing traffic more efficiently.
To accurately troubleshoot your ATM network you should have the following analyzers:
Posted: Fri Apr 9 10:25:00 PDT 1999
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