What to do when the network doesn’t work? Here is where troubleshooting tools come in. In the world of Ethernet, there are a number of common problems that can be identified quickly with the right tools. These include the following:

• Cabling error. The LAN cable is connected to the wrong port.
• Cable fault. There is a problem with the connector resulting in an open or short circuit.
• Speed or duplex mismatch. The NIC is configured for a speed/duplex setting that is incompatible with that of the switch port.
• DHCP error. Stations are unable to obtain an IP address from the DHCP server.
• Duplicate IP address. Multiple devices are configured statically with the same IP address.
• Routing problem. Stations are unable to reach destinations outside the local VLAN either because the default gateway is down or misconfigured.

To diagnose these problems quickly, you need a number of troubleshooting tools that are now packaged in hand-held test units. The following are some of these common tools:

• Cable Tester. This function checks for any cable faults such as open and short circuits. Using Time Domain Reflectometry (TDR), the tester can also determine the length of the connected cable.
• Port Identifier. This function activates and deactivates the Ethernet port thus causing the port LED on the switch to turn on and off periodically. This is useful in identifying the switch port connected to a device.
• Link Status Check. When the test unit is connected to a switch port, this function displays the link status such as the speed, duplex, and flow control.
• DHCP. This allows a test unit to confirm that an IP address can be acquired successfully from the DHCP server.
• Device Scan. This function scans a range of IP addresses looking for active devices.
• PING. This standard function probes an IP address using ICMP. It returns the round-trip delay between the test unit and the target device.
• Traceroute. This standard function traces the IP path to a target address identifying all the intermediate routers.

Got it? Now, go into the field and be confident in your profiling proficiency!

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