Design and maintenance of the Ethernet network must be done with care. Bad network cable can cause a lot of issues, including a significant network slowdown. Older 10 Mbps Ethernet networks were not so affected as modern 100Mbps and 1Gbps networks.
Failed network connection or network slowdown is usually related to a network cable problem. If you plug the cable into the Ethernet adapter and the light doesn’t turn on, it could indicate a problem with either network cable or the ethernet adapter itself. Make sure that the cable is properly connected, but remember that broken cable will not work even then.
Network cable problems can be detected using software or hardware troubleshooting techniques.
Two most important tools are the Ping and Traceroute commands.
Ping (Figure A) operates by sending Internet Control Message Protocol (ICMP) Echo Request packets to the target host and waiting for an ICMP Echo Reply. The program reports errors, packet loss, and a statistical summary of the results, typically including the minimum, maximum, the mean round-trip times, and standard deviation of the mean.
Figure A) Ping command
Traceroute (Figure B) serves a similar purpose, but it tracks the entire network path, reporting similar statistics to Ping.
Figure B) Traceroute command
Common tool for hardware troubleshooting is a simple network cable tester (Figure C), which tests the continuity between the pairs in the twisted-pair cable. There are eight lights on each portion of the unit. One end is plugged in to the patch panel with a patch cable that is known to be good, and the other end is plugged in to the computer’s patch cable. If all eight lights come on, the cable is good. If not, there is a broken wire somewhere in the cable. You can use this cable tester also to test patch cables as they could be source of some network problems. A badly or improperly crimped cable, loose ends or the wrong type of cable connecting the computer to the LAN jack can create a network slowdown.
Advanced network cable testers, known as LAN certifiers (Figure D) can test the network cable for continuity, shorted pairs, and crossed pairs and can determine the length of the cable using a built-in time-delay reflectometer (TDR). The TDR can also determine how far down the cable the fault is located, which can expedite repairing a cabling problem.
Figure C) Simple network cable tester Figure D) LAN certifier
Before start troubleshooting ensure that the network cables you are testing are not too close to the power cables somewhere, as this can cause interference in the Ethernet network.