During a project where I was onsite I discovered a 20-25 years old network cabling, called AMPICCS. This cabling system takes one Cat.5 cable, splits the eight wires into 2x four wires, which serve two ports in a network outlet.
This type of cabling is limited to 100 MBit / Full duplex and only capable for 15.4 Watts Power-over-Ethernet. 1 GBit or new wireless access points which require PoE+ with 30 Watts (like Cisco’s 2800 Series) are not working with this type of cabling system.
If I encounter a “troublesome” network cabling, I’m always using the following commands on a Cisco switch for troubleshooting and hunting for Layer one problems. In my examples shown below, I’m troubleshooting interface Gi1/0/4 on my 3750G Switch:
Show interfaces counters errors
The command show interfaces counters errors outputs the error counters, where the FCS-Errors are indicating cabling problems. FCS stands for Field Checksum Sequence.
Show power inline
The command show power inline shows the Power-over-Ethernet usage, which is useful to check if a device like an IP phone or a wireless access point is getting the PoE power they need. In this output, it shows my Cisco IP Phone 7975G which consumes 12 Watt.
Test cable-diagnostics tdr interface
The command test cable-diagnostics tdr runs a cable diagnostics test, with the show cable-diagnostics tdr command the output can be viewed. The command shows the wire pairs and also the length. This is one of my favorite commands.
Show interfaces transceiver detail
Another one of my favorite commands is show interfaces tranceiver detail, which provides a lot of information of the SFP or SPF+ modules inserted into a switch.
Note: Thanks to Heinz Ulm for finding a typo in the commands.