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This chapter describes the tools available to assist you in troubleshooting your switch router, 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:
The following are some of the most commonly used show commands:
For further information about show commands, refer to the ATM Switch Router Command Reference for your specific software version.
In the 12.0(10)W5(18) system software release, some of the show commands commonly used for troubleshooting have been converted from show epc commands to show controllers commands. The show controllers commands are described in the next section. Table 1 provides the mapping of the command syntax conversion.
The debug privileged EXEC commands 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.
"Debugging a Switch Router," provides an overview of debug commands, including how to use them when you are troubleshooting the switch router.
In many situations, third-party diagnostic tools can be more useful and less intrusive than using debug commands. For more information, see the "Third-Party Troubleshooting Tools" section.
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.
For IP, the ping command sends Internet Control Message Protocol (ICMP) echo messages. If a station receives an ICMP echo message, it sends an ICMP echo reply message back to the source.
Using the extended command mode of the privileged EXEC mode ping command, you can specify the supported IP header options, which allow the switch router to perform a more extensive range of test options. To enter ping extended command mode, enter the ping command at the command prompt followed by a return.
To see how the command works under normal conditions, use the ping command when the network is functioning properly. When you are troubleshooting, you can then see the difference between normal and abnormal operation.
For detailed information about using the ping and extended ping commands, refer to the
Cisco IOS Configuration Fundamentals Command Reference publication.
The traceroute user EXEC command discovers the routes packets follow when traveling to their destinations. With the traceroute privileged EXEC command, the supported IP header options are specified, and the switch router can perform a more extensive range of test options.
The traceroute command works by using the error message generated by switch routers 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 router 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 increases by one.
Each outgoing packet can result in one of two error messages. A "time exceeded" error message indicates that an intermediate switch router 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, the traceroute command displays an asterisk (*).
The traceroute command terminates when the destination responds, when the maximum TTL is exceeded, or when the user interrupts the traceroute command with the escape sequence.
To see how the command works under normal conditions, use the traceroute command when the network is functioning properly. When you are troubleshooting, you can then see the difference between normal and abnormal operation.
For detailed information about using the traceroute and extended traceroute commands, refer to the ATM Switch Router Command Reference .
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 router, 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 check physical connectivity.
Using cable testers (scanners), you can also check physical connectivity. Cable testers are available for foil twisted-pair (FTP), unshielded twisted-pair (UTP), 10BaseT, and coaxial and twinax cables. A given cable tester can perform any of the following functions:
Similar testing equipment is available for fiber-optic cable. Due to the relatively high cost of fiber cable and its installation, test fiber-optic cable 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 quickly locate open circuits, 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 the time it takes for the signal to reflect and calculates the distance to a fault in the cable. TDRs can also measure the length of a cable, and some TDRs can calculate the rate of propagation based on a configured cable length.
Fiber-optic measurement is performed by an optical time domain reflectometer (OTDR). OTDRs can accurately measure the length of the fiber, locate cable breaks, measure the fiber attenuation, and measure splice or connector losses. An OTDR can take the signature of a particular installation, noting attenuation and splice losses. This baseline measurement can then be compared with future signatures when you suspect a problem in the system.
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:
Most physical layer analyzers can perform many of the following functions:
Most network analyzers can perform many of the following functions:
Posted: Wed Jan 22 00:06:44 PST 2003
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