Your network might have hundreds, if not thousands of Ethernet cables throughout the infrastructure. These might be station cords in cubicles connecting VoIP phones and desktops, or in data centers connecting storage arrays to server farms.
There are many reasons that cabling can create problems in an environment:
When cabling starts to fail, three possible problems occur:
Cable faults can be found by looking for Ethernet symbol errors on switch and router interfaces. This is the first clue that there is a problem, as the Ethernet chipset must do single bit error correction to pass a valid frame on to layer-2.
For a secondary indication, look for the presence of FCS errors when there are no alignment errors on the interface.
Note: | FCS Errors along with alignment errors and no collisions are indicative of a full duplex mismatched to a half duplex. |
For a tertiary indication, look for interfaces that have multiple Carrier Sense Error occurrences. If an interface has all of the above, then it is completely safe to assume that there is a cabling issue plaguing the connection.
Note: | Many switch and router manufacturers do not present these error counters via their web UI or CLI. In many cases, individual SNMP OIDs must be queried to see these statistics.
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These OIDs should be queried on every interface in the infrastructure and analysed to determine where there are problems.
When you find an interface that has Symbol Errors, FCS Errors (without alignment errors), and/or Carrier Sense errors, you should perform a manual inspection of the cabling involved. Look for the problems listed below in the involved cabling:
Sometimes just replacing a patch cord with a known good one will remedy the problem.
Note: | When throwing away a suspected bad patch cord, always cut the ends off both ends of the cord. Otherwise, you may have someone "rescue" the patch cord from the trash can and attempt to use it elsewhere in the network, thinking it is a perfectly good patch cord. |
If the problem is not readily apparent or visible, you may need to deploy a cable tester. The type of cable tester should not be a basic "pair continuity" type of tester that sells for under $100, but a professional grade cable tester that performs the following signal tests:
Some vendors in this market are:
PathSolutions TotalView automatically collects the appropriate error counters and includes a Heuristics Prescription Engine that can spot physical layer issues in your network automatically. The Cabling Predictor feature will identify where you have symbol errors anywhere in your environment, so problems can be remedied before packets are lost.
Network troubleshooting and cabling/connection problems can be prevented if the right information is brought to bear about your network's performance and configuration.
Review our network troubleshooting white paper or contact us with questions about how PathSolutions TotalView can make network troubleshooting easier.