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This chapter describes the tools available to assist you in troubleshooting your ATM switch and contains the following sections:
You can use the show, debug, ping, and traceroute commands to monitor and troubleshoot your internetwork.
You can use the show commands to perform many functions:
Following are some of the most commonly used show commands:
| Command | Description |
|---|---|
show ip | Displays IP configuration and statistics |
show interfaces | Displays statistics for the network interfaces |
show controllers | Displays statistics for port adapter interface controllers |
show lane | Displays LAN Emulation configuration |
show running-config | Displays the switch configuration currently running |
show startup-config | Displays the switch configuration stored in nonvolatile RAM (NVRAM) |
show flash | Group of commands that display the layout and contents of Flash memory |
show buffers | Displays statistics for the buffer pools on the switch |
show memory | Shows statistics about the switch memory, including free pool statistics |
show processes | Displays information about the active processes on the switch |
show stacks | Displays information about the stack utilization of processes and interrupt routines, in addition to the reason for the last system reboot |
show version | Displays the configuration of the system hardware, the software version, the names and sources of configuration files, and the boot images |
For information about 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 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 an ATM Switch" provides an overview of debug commands and using them when you are 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 "Third-Party Troubleshooting Tools," later in this chapter.
To check host reachability and network connectivity, use the ping user EXEC 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, which 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.
Use 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 about 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 packets 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.
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 about using the traceroute and extended traceroute commands, refer to the LightStream 1010 ATM Switch Software Command Reference publication.
In many situations, third-party diagnostic tools can be helpful. For example, attaching a network analyzer to a network is less intrusive and is more likely to yield useful information without interrupting the operation of the switch than using the debug commands which are processor intensive.
Some typical third-party tools used for troubleshooting internetworks are described in the following sections:
Volt-ohm meters and digital multimeters 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.
TDRs can quickly locate open and short circuits, crimps, kinks, sharp bends, impedance mismatches, and other defects in metallic cables.
A TDR reflects a signal off the end of the cable. Opens, shorts, and other problems reflect back the signal 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 rate of propagation based on a configured cable length.
Network monitors continuously track packets crossing a network, providing an accurate picture of network activity. Network monitors do not decode the contents of frames. They are useful for creating a baseline of normal performance.
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 and assist in locating traffic overloads, planning for network expansion, detecting intruders, and distributing traffic more efficiently.
To accurately troubleshoot your ATM network you should have the following analyzers:
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