Information Technology Reference
In-Depth Information
•
Accurate representation of the physical network for VLAN design and configuration verification
•
Capability to obtain VLAN configuration information on a specific device or link interface
•
Discrepancy reports on conflicting configurations
•
Capability to troubleshoot and identify individual device configurations that are in error with
system-level VLANs
•
Quick detection of changes in VLAN status of switch ports
•
User authentication and write protection security
Third-Party Troubleshooting Tools
In many situations, third-party diagnostic tools can be more useful than commands that are integrated
into the router. 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 router. The following are some typical third-party troubleshooting tools used for
troubleshooting internetworks:
•
Volt-ohm meters, digital multimeters, and cable testers are useful in testing the physical connectivity
of your cable plant.
•
Time domain reflectors (TDRs) and optical time domain reflectors (OTDRs) are devices that assist
in the location of cable breaks, impedance mismatches, and other physical cable plant problems.
•
Breakout boxes, fox boxes, and BERTs/BLERTs are useful for troubleshooting problems in
peripheral interfaces.
•
Network monitors provide an accurate picture of network activity over a period of time by
continuously tracking packets crossing a network.
•
Network analyzers such as sniffers decode problems at all seven OSI layers and can be identified
automatically in real time, providing a clear view of network activity and categorizing problems by
criticality.
Volt-Ohm Meters, Digital Multimeters, and Cable Testers
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.
Cable testers (scanners) also enable you to check physical connectivity. Cable testers are available for
shielded twisted-pair (STP), unshielded twisted-pair (UTP), 10BaseT, and coaxial and twinax cables. A
given cable tester might be capable of performing any of the following functions:
•
Test and report on cable conditions, including near-end crosstalk (NEXT), attenuation, and noise
•
Perform TDR, traffic monitoring, and wire map functions
•
Display Media Access Control (MAC)-layer information about LAN traffic, provide statistics such
as network utilization and packet error rates, and perform limited protocol testing (for example,
TCP/IP tests such as
ping
)
Similar testing equipment is available for fiber-optic cable. Because of the relatively high cost of this
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
