Diagnostic Copper Wire Test on SG200-26 Gigabit Switch - What is the "Open Cable" telling me?

[txlombardi_2]

I installed a Cisco SG200-26 Gigabit Switch at a customer's facility.  They have some severe latency on their network, so I hoped the switches reporting abilities would help me track down the problem.  There are 7 white box computers on the switch.  Six of the computers were sold at the same time and have the same motherboard.  A seventh computer was sold a couple of years later and has a different motherboard.  All computers have the NIC on the motherboard.  All seven computers come up with "Open Cable - Cable is connected on only one side" when the copper test is run on the Diagnostics tab.  Each test has at lease three of the four wire pairs reporting an 8 NS skew.  A router, a Dell server, a Cisco wireless router used only as an access point, an old computer (about 10 years old) and a small Netgear switch all show okay in the copper test.  Every node is at gigabit speed except the Netgear switch and the old computer.  None of the ports to which the computers are attached show errors. 

Thinking maybe the facility wiring is all bad, I took one computer to the switch and connected a known, good 5' network patch cable from the computer to the Cisco SG200-26 Gigabit Switch and then I did a copper test.  The results were the same - "Open Cable - Cable is connected on only one side." 

I am thoroughly confused by all this.  First of all, what exactly does "Open Cable - Cable is connected on only one side" mean?  These computers can access the server and the Internet and at times seem to have normal access times to resources, so I know both ends of the cable are connected.  And what is the skew trying to tell me?  Is it possible that all 7 computers, which are Windows 7 32 bit and a couple of 64 bit operating systems are having a driver problem?

Some help here would be most appreciated.

[Aleksandra Dargiel · Accepted solution]

Hi txlmbardi_2,

This is really not expected behavior thus please open ticket with Cisco Small Business Support team to investigate this further:

http://www.cisco.com/c/en/us/support/web/tsd-cisco-small-business-support-center-contacts.html

Regards,

Aleksandra

[txlombardi_2]

Thank you for your reply.  I did contact Cisco support and they agree with you.  The switch should not be doing what it is doing with the copper test.  They don't have an answer, but I am pursuing it and a case is open.

[Aleksandra Dargiel]

Hi Tomi,

I wonder if there is no patch panel in your lab.

Regards,

Aleksandra

[txlombardi_2]

As a matter of fact, you are correct.  The client does not have a patch panel.  This is a live, production network that was cabled years before they called me in to manage it.  I hate the way it is setup and in particular the absence of a patch panel, but unless I give the client a good reason, there is no way they will spend the money to put one in.

Do you think the absence of a patch panel has something to do with the "open cable" message the copper test is reporting only on the seven workstations?  Every other connection comes up okay.

[Aleksandra Dargiel]

Hi Tomi,

Being honest I have seen the opposite behavior. The cable test is also used by Green Ethernet option to detect the length of the cable and adjust the power if it is below 50m. I have seen that patch panel or any other type intermediate connector would cause the test to detect this length incorrectly.

So since the patch panel is not present on this particular network I would check the cabling for this seven workstations. At least as a start point.

Regards,

Aleksandra

[txlombardi_2]

While the cable itself certainly can be the problem, I sort of ruled that out when I carried one computer to the equipment room and connected it directly to the switch with a 5' network cable that was used on the one older computer where the open cable fault is not occurring.  In other words, a known good cable connected to one of the problem computers still displays the fault.  This was noted in my original post.